Regular Expressions and stringr

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# Regular Expressions and stringr
## Pavitra Chakravarty
### R-Ladies Cologne, R-Ladies Gaborone

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### What are regular expressions?

+ Regular expression is a pattern that describes a specific set of strings with a common structure
+ Heavily used for string matching / replacing in all programming languages
+ Heart and soul for string operations

---

### Regular expression syntax

6 basic canonical characteristics of regular expressions

+ __basic pattern matching__: Using functions from stringr package with exact sequence of characters
  
  + `str_detect()`, `str_subset()`, `str_view()`, `str_view_all()`

+ __anchors__: Indicate start and stop of sentence

+ `^: indicating start of sentence`, `$: indicating end of sentence`
 
+ __escape characters__: special characters cannot be directly coded in string
 
  + `\`: if you want to find strings with single quote `'`, "escape" single quote by preceding it with `\`
  
---

+ __character classes__: specify entire classes of characters, such as numbers, letters, etc using either `[:` and `:]` around        predefined name or  `\` and a special character
  
  + `[:digit:]` or `\d`: digits, 0 1 2 3 4 5 6 7 8 9, equivalent to `[0-9]` 
  + `\D`: non-digits, equivalent to `[^0-9]`  
  + `[:lower:]`: lower-case letters, equivalent to `[a-z]`  
  + `[:upper:]`: upper-case letters, equivalent to `[A-Z]` 
  + `[:alpha:]`: alphabetic characters, equivalent to `[[:lower:][:upper:]]` or `[A-z]` 
  + `[:alnum:]`: alphanumeric characters, equivalent to `[[:alpha:][:digit:]]` or `[A-z0-9]`   
  + `\w`: word characters, equivalent to `[[:alnum:]_]` or `[A-z0-9_]` 
  + `\W`: not word, equivalent to `[^A-z0-9_]`  
  + `[:blank:]`: blank characters, i.e. space and tab 
  * `[:space:]`: space characters: tab, newline, vertical tab, form feed, carriage return, space
  * `\s`: space, ` `  
  * `\S`: not space  
  
+ __quantifiers__: Quantifiers specify how many repetitions of the pattern

+ `*`: matches at least 0 times   
  + `+`: matches at least 1 times     
  + `?`: matches at most 1 times   
  + `{n}`: matches exactly n times   
  + `{n,}`: matches at least n times
  + `{n,m}`: matches between n and m times

+ __character clusters__: Use of paranthesis to keep pattern together

+ `()`: use with pattern-matching characters to create groups
  
---
  
### Dataset being used today

```r
library(tidyverse)

enron <- read_csv("https://raw.githubusercontent.com/UBC-STAT/stat545.stat.ubc.ca/master/content/data/enron/enron.csv") %>% drop_na()

glimpse(enron)
```

```
## Rows: 214,195
## Columns: 3
## $ mail_num <dbl> 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 10, 10, 10, 1…
## $ person <chr> "allen-p", "allen-p", "allen-p", "allen-p", "allen-p", "allen…
## $ email <chr> "Message-ID: <18782981.1075855378110.JavaMail.evans@thyme>", …
```

```r
head(enron, n=50)
```

```
## # A tibble: 50 × 3
## mail_num person email 
## <dbl> <chr> <chr> 
## 1 1 allen-p Message-ID: <18782981.1075855378110.JavaMail.evans@thyme>
## 2 1 allen-p Date: Mon, 14 May 2001 16:39:00 -0700 (PDT) 
## 3 1 allen-p From: phillip.allen@enron.com 
## 4 1 allen-p To: tim.belden@enron.com 
## 5 1 allen-p Subject: 
## 6 1 allen-p Mime-Version: 1.0 
## 7 1 allen-p Content-Type: text/plain; charset=us-ascii 
## 8 1 allen-p Content-Transfer-Encoding: 7bit 
## 9 1 allen-p X-From: Phillip K Allen 
## 10 1 allen-p X-To: Tim Belden <Tim Belden/Enron@EnronXGate> 
## # … with 40 more rows
```

---

### Canonical principle #1: Basic pattern-matching

```r
enron %>% filter(str_detect(enron$person, "Allen"))
```

```
## # A tibble: 0 × 3
## # … with 3 variables: mail_num <dbl>, person <chr>, email <chr>
```

```r
str_subset(enron$email, "tracy.ngo")
```

```
## [1] "To: tracy.ngo@enron.com"                                               
## [2] "To: tracy.ngo@enron.com"                                               
## [3] "To: tim.belden@enron.com, steve.c.hall@enron.com, tracy.ngo@enron.com,"
```

```r
str_view_all(enron$email, "tracy.ngo")
```

---

### Canonical principle #2: Anchors

+ `^`: matches the start of the string.   
  + `$`: matches the end of the string.   
  + `\b`: matches the empty string at either edge of a _word_. Don't confuse it with `^ $` which marks the edge of a _string_.   
  + `\B`: matches the empty string provided it is not at an edge of a word.

```r
enron %>% filter(str_detect(enron$email, "@ECT")) %>% select 
```

```
## # A tibble: 6,524 × 0
```

```r
enron %>% filter(str_detect(enron$email, "weekend$"))
```

```
## # A tibble: 45 × 3
## mail_num person email 
## <dbl> <chr> <chr> 
## 1 69 allen-p morning I sent you the roll did you get it? Did you need m…
## 2 94 carson-m Subject: This weekend 
## 3 94 carson-m Subject: This weekend 
## 4 95 carson-m Subject: Re: This weekend 
## 5 69 davis-d Subject: Manual JE info for cutover weekend 
## 6 69 davis-d Subject: Manual JE info for cutover weekend 
## 7 69 davis-d Subject: Manual JE info for cutover weekend 
## 8 1 dean-c Subject: RE: This weekend 
## 9 1 dean-c Subject: RE: This weekend 
## 10 1 dean-c Subject: RE: This weekend 
## # … with 35 more rows
```
---

### Canonical principle #3: Escape characters

```r
x <- c("123-456-7890", "(123)456-7890", "(123) 456-7890", "1235-2351")
str_view(x, "(\\d\\d\\d)\\d\\d\\d-\\d\\d\\d\\d")
```

<div id="htmlwidget-9294715df79023387532" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-9294715df79023387532">{"x":{"html":"<ul>\n <li>123-456-7890<\/li>\n <li>(123)456-7890<\/li>\n <li>(123) 456-7890<\/li>\n <li>1235-2351<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>
---

```r
str_view("so it goes $^$ here", "\\$\\^\\$")
```

<div id="htmlwidget-113bfd10f05eee3413f0" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-113bfd10f05eee3413f0">{"x":{"html":"<ul>\n <li>so it goes $^$<\/span> here<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>

---

### Canonical principle #4: Character Classes

```r
str_view(stringr::words, "^[yx]", match=TRUE)
```

<div id="htmlwidget-c27e65e985df2733053b" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-c27e65e985df2733053b">{"x":{"html":"<ul>\n <li>y<\/span>ear<\/li>\n <li>y<\/span>es<\/li>\n <li>y<\/span>esterday<\/li>\n <li>y<\/span>et<\/li>\n <li>y<\/span>ou<\/li>\n <li>y<\/span>oung<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>

---

```r
str_view(stringr::words, "[^e]ed$", match = TRUE)
```

<div id="htmlwidget-7046bf24911a0f946cb3" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-7046bf24911a0f946cb3">{"x":{"html":"<ul>\n <li>bed<\/span><\/li>\n <li>hundred<\/span><\/li>\n <li>red<\/span><\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>

---

```r
str_view(c("red", "reed"), "[^e]ed$", match = FALSE)
```

<div id="htmlwidget-27abd20b6bfed0c0d201" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-27abd20b6bfed0c0d201">{"x":{"html":"<ul>\n <li>reed<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>

---

```r
str_view(stringr::words, "^(thr)*", match = TRUE)
```

<div id="htmlwidget-634cc4af11296594161c" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-634cc4af11296594161c">{"x":{"html":"<ul>\n <li><\/span>a<\/li>\n <li><\/span>able<\/li>\n <li><\/span>about<\/li>\n <li><\/span>absolute<\/li>\n <li><\/span>accept<\/li>\n <li><\/span>account<\/li>\n <li><\/span>achieve<\/li>\n <li><\/span>across<\/li>\n <li><\/span>act<\/li>\n <li><\/span>active<\/li>\n <li><\/span>actual<\/li>\n <li><\/span>add<\/li>\n <li><\/span>address<\/li>\n <li><\/span>admit<\/li>\n <li><\/span>advertise<\/li>\n <li><\/span>affect<\/li>\n <li><\/span>afford<\/li>\n <li><\/span>after<\/li>\n <li><\/span>afternoon<\/li>\n <li><\/span>again<\/li>\n <li><\/span>against<\/li>\n <li><\/span>age<\/li>\n <li><\/span>agent<\/li>\n <li><\/span>ago<\/li>\n <li><\/span>agree<\/li>\n <li><\/span>air<\/li>\n <li><\/span>all<\/li>\n <li><\/span>allow<\/li>\n <li><\/span>almost<\/li>\n <li><\/span>along<\/li>\n <li><\/span>already<\/li>\n <li><\/span>alright<\/li>\n <li><\/span>also<\/li>\n <li><\/span>although<\/li>\n <li><\/span>always<\/li>\n <li><\/span>america<\/li>\n <li><\/span>amount<\/li>\n <li><\/span>and<\/li>\n <li><\/span>another<\/li>\n <li><\/span>answer<\/li>\n <li><\/span>any<\/li>\n <li><\/span>apart<\/li>\n <li><\/span>apparent<\/li>\n <li><\/span>appear<\/li>\n <li><\/span>apply<\/li>\n <li><\/span>appoint<\/li>\n <li><\/span>approach<\/li>\n <li><\/span>appropriate<\/li>\n <li><\/span>area<\/li>\n <li><\/span>argue<\/li>\n <li><\/span>arm<\/li>\n <li><\/span>around<\/li>\n <li><\/span>arrange<\/li>\n <li><\/span>art<\/li>\n <li><\/span>as<\/li>\n <li><\/span>ask<\/li>\n <li><\/span>associate<\/li>\n <li><\/span>assume<\/li>\n <li><\/span>at<\/li>\n <li><\/span>attend<\/li>\n <li><\/span>authority<\/li>\n <li><\/span>available<\/li>\n <li><\/span>aware<\/li>\n <li><\/span>away<\/li>\n <li><\/span>awful<\/li>\n <li><\/span>baby<\/li>\n <li><\/span>back<\/li>\n <li><\/span>bad<\/li>\n <li><\/span>bag<\/li>\n <li><\/span>balance<\/li>\n <li><\/span>ball<\/li>\n <li><\/span>bank<\/li>\n <li><\/span>bar<\/li>\n <li><\/span>base<\/li>\n <li><\/span>basis<\/li>\n <li><\/span>be<\/li>\n <li><\/span>bear<\/li>\n <li><\/span>beat<\/li>\n <li><\/span>beauty<\/li>\n <li><\/span>because<\/li>\n <li><\/span>become<\/li>\n <li><\/span>bed<\/li>\n <li><\/span>before<\/li>\n <li><\/span>begin<\/li>\n <li><\/span>behind<\/li>\n <li><\/span>believe<\/li>\n <li><\/span>benefit<\/li>\n <li><\/span>best<\/li>\n <li><\/span>bet<\/li>\n <li><\/span>between<\/li>\n <li><\/span>big<\/li>\n <li><\/span>bill<\/li>\n <li><\/span>birth<\/li>\n <li><\/span>bit<\/li>\n <li><\/span>black<\/li>\n <li><\/span>bloke<\/li>\n <li><\/span>blood<\/li>\n <li><\/span>blow<\/li>\n <li><\/span>blue<\/li>\n <li><\/span>board<\/li>\n <li><\/span>boat<\/li>\n <li><\/span>body<\/li>\n <li><\/span>book<\/li>\n <li><\/span>both<\/li>\n <li><\/span>bother<\/li>\n <li><\/span>bottle<\/li>\n <li><\/span>bottom<\/li>\n <li><\/span>box<\/li>\n <li><\/span>boy<\/li>\n <li><\/span>break<\/li>\n <li><\/span>brief<\/li>\n <li><\/span>brilliant<\/li>\n <li><\/span>bring<\/li>\n <li><\/span>britain<\/li>\n <li><\/span>brother<\/li>\n <li><\/span>budget<\/li>\n <li><\/span>build<\/li>\n <li><\/span>bus<\/li>\n <li><\/span>business<\/li>\n <li><\/span>busy<\/li>\n <li><\/span>but<\/li>\n <li><\/span>buy<\/li>\n <li><\/span>by<\/li>\n <li><\/span>cake<\/li>\n <li><\/span>call<\/li>\n <li><\/span>can<\/li>\n <li><\/span>car<\/li>\n <li><\/span>card<\/li>\n <li><\/span>care<\/li>\n <li><\/span>carry<\/li>\n <li><\/span>case<\/li>\n <li><\/span>cat<\/li>\n <li><\/span>catch<\/li>\n <li><\/span>cause<\/li>\n <li><\/span>cent<\/li>\n <li><\/span>centre<\/li>\n <li><\/span>certain<\/li>\n <li><\/span>chair<\/li>\n <li><\/span>chairman<\/li>\n <li><\/span>chance<\/li>\n <li><\/span>change<\/li>\n <li><\/span>chap<\/li>\n <li><\/span>character<\/li>\n <li><\/span>charge<\/li>\n <li><\/span>cheap<\/li>\n <li><\/span>check<\/li>\n <li><\/span>child<\/li>\n <li><\/span>choice<\/li>\n <li><\/span>choose<\/li>\n <li><\/span>Christ<\/li>\n <li><\/span>Christmas<\/li>\n <li><\/span>church<\/li>\n <li><\/span>city<\/li>\n <li><\/span>claim<\/li>\n <li><\/span>class<\/li>\n <li><\/span>clean<\/li>\n <li><\/span>clear<\/li>\n <li><\/span>client<\/li>\n <li><\/span>clock<\/li>\n <li><\/span>close<\/li>\n <li><\/span>closes<\/li>\n <li><\/span>clothe<\/li>\n <li><\/span>club<\/li>\n <li><\/span>coffee<\/li>\n <li><\/span>cold<\/li>\n <li><\/span>colleague<\/li>\n <li><\/span>collect<\/li>\n <li><\/span>college<\/li>\n <li><\/span>colour<\/li>\n <li><\/span>come<\/li>\n <li><\/span>comment<\/li>\n <li><\/span>commit<\/li>\n <li><\/span>committee<\/li>\n <li><\/span>common<\/li>\n <li><\/span>community<\/li>\n <li><\/span>company<\/li>\n <li><\/span>compare<\/li>\n <li><\/span>complete<\/li>\n <li><\/span>compute<\/li>\n <li><\/span>concern<\/li>\n <li><\/span>condition<\/li>\n <li><\/span>confer<\/li>\n <li><\/span>consider<\/li>\n <li><\/span>consult<\/li>\n <li><\/span>contact<\/li>\n <li><\/span>continue<\/li>\n <li><\/span>contract<\/li>\n <li><\/span>control<\/li>\n <li><\/span>converse<\/li>\n <li><\/span>cook<\/li>\n <li><\/span>copy<\/li>\n <li><\/span>corner<\/li>\n <li><\/span>correct<\/li>\n <li><\/span>cost<\/li>\n <li><\/span>could<\/li>\n <li><\/span>council<\/li>\n <li><\/span>count<\/li>\n <li><\/span>country<\/li>\n <li><\/span>county<\/li>\n <li><\/span>couple<\/li>\n <li><\/span>course<\/li>\n <li><\/span>court<\/li>\n <li><\/span>cover<\/li>\n <li><\/span>create<\/li>\n <li><\/span>cross<\/li>\n <li><\/span>cup<\/li>\n <li><\/span>current<\/li>\n <li><\/span>cut<\/li>\n <li><\/span>dad<\/li>\n <li><\/span>danger<\/li>\n <li><\/span>date<\/li>\n <li><\/span>day<\/li>\n <li><\/span>dead<\/li>\n <li><\/span>deal<\/li>\n <li><\/span>dear<\/li>\n <li><\/span>debate<\/li>\n <li><\/span>decide<\/li>\n <li><\/span>decision<\/li>\n <li><\/span>deep<\/li>\n <li><\/span>definite<\/li>\n <li><\/span>degree<\/li>\n <li><\/span>department<\/li>\n <li><\/span>depend<\/li>\n <li><\/span>describe<\/li>\n <li><\/span>design<\/li>\n <li><\/span>detail<\/li>\n <li><\/span>develop<\/li>\n <li><\/span>die<\/li>\n <li><\/span>difference<\/li>\n <li><\/span>difficult<\/li>\n <li><\/span>dinner<\/li>\n <li><\/span>direct<\/li>\n <li><\/span>discuss<\/li>\n <li><\/span>district<\/li>\n <li><\/span>divide<\/li>\n <li><\/span>do<\/li>\n <li><\/span>doctor<\/li>\n <li><\/span>document<\/li>\n <li><\/span>dog<\/li>\n <li><\/span>door<\/li>\n <li><\/span>double<\/li>\n <li><\/span>doubt<\/li>\n <li><\/span>down<\/li>\n <li><\/span>draw<\/li>\n <li><\/span>dress<\/li>\n <li><\/span>drink<\/li>\n <li><\/span>drive<\/li>\n <li><\/span>drop<\/li>\n <li><\/span>dry<\/li>\n <li><\/span>due<\/li>\n <li><\/span>during<\/li>\n <li><\/span>each<\/li>\n <li><\/span>early<\/li>\n <li><\/span>east<\/li>\n <li><\/span>easy<\/li>\n <li><\/span>eat<\/li>\n <li><\/span>economy<\/li>\n <li><\/span>educate<\/li>\n <li><\/span>effect<\/li>\n <li><\/span>egg<\/li>\n <li><\/span>eight<\/li>\n <li><\/span>either<\/li>\n <li><\/span>elect<\/li>\n <li><\/span>electric<\/li>\n <li><\/span>eleven<\/li>\n <li><\/span>else<\/li>\n <li><\/span>employ<\/li>\n <li><\/span>encourage<\/li>\n <li><\/span>end<\/li>\n <li><\/span>engine<\/li>\n <li><\/span>english<\/li>\n <li><\/span>enjoy<\/li>\n <li><\/span>enough<\/li>\n <li><\/span>enter<\/li>\n <li><\/span>environment<\/li>\n <li><\/span>equal<\/li>\n <li><\/span>especial<\/li>\n <li><\/span>europe<\/li>\n <li><\/span>even<\/li>\n <li><\/span>evening<\/li>\n <li><\/span>ever<\/li>\n <li><\/span>every<\/li>\n <li><\/span>evidence<\/li>\n <li><\/span>exact<\/li>\n <li><\/span>example<\/li>\n <li><\/span>except<\/li>\n <li><\/span>excuse<\/li>\n <li><\/span>exercise<\/li>\n <li><\/span>exist<\/li>\n <li><\/span>expect<\/li>\n <li><\/span>expense<\/li>\n <li><\/span>experience<\/li>\n <li><\/span>explain<\/li>\n <li><\/span>express<\/li>\n <li><\/span>extra<\/li>\n <li><\/span>eye<\/li>\n <li><\/span>face<\/li>\n <li><\/span>fact<\/li>\n <li><\/span>fair<\/li>\n <li><\/span>fall<\/li>\n <li><\/span>family<\/li>\n <li><\/span>far<\/li>\n <li><\/span>farm<\/li>\n <li><\/span>fast<\/li>\n <li><\/span>father<\/li>\n <li><\/span>favour<\/li>\n <li><\/span>feed<\/li>\n <li><\/span>feel<\/li>\n <li><\/span>few<\/li>\n <li><\/span>field<\/li>\n <li><\/span>fight<\/li>\n <li><\/span>figure<\/li>\n <li><\/span>file<\/li>\n <li><\/span>fill<\/li>\n <li><\/span>film<\/li>\n <li><\/span>final<\/li>\n <li><\/span>finance<\/li>\n <li><\/span>find<\/li>\n <li><\/span>fine<\/li>\n <li><\/span>finish<\/li>\n <li><\/span>fire<\/li>\n <li><\/span>first<\/li>\n <li><\/span>fish<\/li>\n <li><\/span>fit<\/li>\n <li><\/span>five<\/li>\n <li><\/span>flat<\/li>\n <li><\/span>floor<\/li>\n <li><\/span>fly<\/li>\n <li><\/span>follow<\/li>\n <li><\/span>food<\/li>\n <li><\/span>foot<\/li>\n <li><\/span>for<\/li>\n <li><\/span>force<\/li>\n <li><\/span>forget<\/li>\n <li><\/span>form<\/li>\n <li><\/span>fortune<\/li>\n <li><\/span>forward<\/li>\n <li><\/span>four<\/li>\n <li><\/span>france<\/li>\n <li><\/span>free<\/li>\n <li><\/span>friday<\/li>\n <li><\/span>friend<\/li>\n <li><\/span>from<\/li>\n <li><\/span>front<\/li>\n <li><\/span>full<\/li>\n <li><\/span>fun<\/li>\n <li><\/span>function<\/li>\n <li><\/span>fund<\/li>\n <li><\/span>further<\/li>\n <li><\/span>future<\/li>\n <li><\/span>game<\/li>\n <li><\/span>garden<\/li>\n <li><\/span>gas<\/li>\n <li><\/span>general<\/li>\n <li><\/span>germany<\/li>\n <li><\/span>get<\/li>\n <li><\/span>girl<\/li>\n <li><\/span>give<\/li>\n <li><\/span>glass<\/li>\n <li><\/span>go<\/li>\n <li><\/span>god<\/li>\n <li><\/span>good<\/li>\n <li><\/span>goodbye<\/li>\n <li><\/span>govern<\/li>\n <li><\/span>grand<\/li>\n <li><\/span>grant<\/li>\n <li><\/span>great<\/li>\n <li><\/span>green<\/li>\n <li><\/span>ground<\/li>\n <li><\/span>group<\/li>\n <li><\/span>grow<\/li>\n <li><\/span>guess<\/li>\n <li><\/span>guy<\/li>\n <li><\/span>hair<\/li>\n <li><\/span>half<\/li>\n <li><\/span>hall<\/li>\n <li><\/span>hand<\/li>\n <li><\/span>hang<\/li>\n <li><\/span>happen<\/li>\n <li><\/span>happy<\/li>\n <li><\/span>hard<\/li>\n <li><\/span>hate<\/li>\n <li><\/span>have<\/li>\n <li><\/span>he<\/li>\n <li><\/span>head<\/li>\n <li><\/span>health<\/li>\n <li><\/span>hear<\/li>\n <li><\/span>heart<\/li>\n <li><\/span>heat<\/li>\n <li><\/span>heavy<\/li>\n <li><\/span>hell<\/li>\n <li><\/span>help<\/li>\n <li><\/span>here<\/li>\n <li><\/span>high<\/li>\n <li><\/span>history<\/li>\n <li><\/span>hit<\/li>\n <li><\/span>hold<\/li>\n <li><\/span>holiday<\/li>\n <li><\/span>home<\/li>\n <li><\/span>honest<\/li>\n <li><\/span>hope<\/li>\n <li><\/span>horse<\/li>\n <li><\/span>hospital<\/li>\n <li><\/span>hot<\/li>\n <li><\/span>hour<\/li>\n <li><\/span>house<\/li>\n <li><\/span>how<\/li>\n <li><\/span>however<\/li>\n <li><\/span>hullo<\/li>\n <li><\/span>hundred<\/li>\n <li><\/span>husband<\/li>\n <li><\/span>idea<\/li>\n <li><\/span>identify<\/li>\n <li><\/span>if<\/li>\n <li><\/span>imagine<\/li>\n <li><\/span>important<\/li>\n <li><\/span>improve<\/li>\n <li><\/span>in<\/li>\n <li><\/span>include<\/li>\n <li><\/span>income<\/li>\n <li><\/span>increase<\/li>\n <li><\/span>indeed<\/li>\n <li><\/span>individual<\/li>\n <li><\/span>industry<\/li>\n <li><\/span>inform<\/li>\n <li><\/span>inside<\/li>\n <li><\/span>instead<\/li>\n <li><\/span>insure<\/li>\n <li><\/span>interest<\/li>\n <li><\/span>into<\/li>\n <li><\/span>introduce<\/li>\n <li><\/span>invest<\/li>\n <li><\/span>involve<\/li>\n <li><\/span>issue<\/li>\n <li><\/span>it<\/li>\n <li><\/span>item<\/li>\n <li><\/span>jesus<\/li>\n <li><\/span>job<\/li>\n <li><\/span>join<\/li>\n <li><\/span>judge<\/li>\n <li><\/span>jump<\/li>\n <li><\/span>just<\/li>\n <li><\/span>keep<\/li>\n <li><\/span>key<\/li>\n <li><\/span>kid<\/li>\n <li><\/span>kill<\/li>\n <li><\/span>kind<\/li>\n <li><\/span>king<\/li>\n <li><\/span>kitchen<\/li>\n <li><\/span>knock<\/li>\n <li><\/span>know<\/li>\n <li><\/span>labour<\/li>\n <li><\/span>lad<\/li>\n <li><\/span>lady<\/li>\n <li><\/span>land<\/li>\n <li><\/span>language<\/li>\n <li><\/span>large<\/li>\n <li><\/span>last<\/li>\n <li><\/span>late<\/li>\n <li><\/span>laugh<\/li>\n <li><\/span>law<\/li>\n <li><\/span>lay<\/li>\n <li><\/span>lead<\/li>\n <li><\/span>learn<\/li>\n <li><\/span>leave<\/li>\n <li><\/span>left<\/li>\n <li><\/span>leg<\/li>\n <li><\/span>less<\/li>\n <li><\/span>let<\/li>\n <li><\/span>letter<\/li>\n <li><\/span>level<\/li>\n <li><\/span>lie<\/li>\n <li><\/span>life<\/li>\n <li><\/span>light<\/li>\n <li><\/span>like<\/li>\n <li><\/span>likely<\/li>\n <li><\/span>limit<\/li>\n <li><\/span>line<\/li>\n <li><\/span>link<\/li>\n <li><\/span>list<\/li>\n <li><\/span>listen<\/li>\n <li><\/span>little<\/li>\n <li><\/span>live<\/li>\n <li><\/span>load<\/li>\n <li><\/span>local<\/li>\n <li><\/span>lock<\/li>\n <li><\/span>london<\/li>\n <li><\/span>long<\/li>\n <li><\/span>look<\/li>\n <li><\/span>lord<\/li>\n <li><\/span>lose<\/li>\n <li><\/span>lot<\/li>\n <li><\/span>love<\/li>\n <li><\/span>low<\/li>\n <li><\/span>luck<\/li>\n <li><\/span>lunch<\/li>\n <li><\/span>machine<\/li>\n <li><\/span>main<\/li>\n <li><\/span>major<\/li>\n <li><\/span>make<\/li>\n <li><\/span>man<\/li>\n <li><\/span>manage<\/li>\n <li><\/span>many<\/li>\n <li><\/span>mark<\/li>\n <li><\/span>market<\/li>\n <li><\/span>marry<\/li>\n <li><\/span>match<\/li>\n <li><\/span>matter<\/li>\n <li><\/span>may<\/li>\n <li><\/span>maybe<\/li>\n <li><\/span>mean<\/li>\n <li><\/span>meaning<\/li>\n <li><\/span>measure<\/li>\n <li><\/span>meet<\/li>\n <li><\/span>member<\/li>\n <li><\/span>mention<\/li>\n <li><\/span>middle<\/li>\n <li><\/span>might<\/li>\n <li><\/span>mile<\/li>\n <li><\/span>milk<\/li>\n <li><\/span>million<\/li>\n <li><\/span>mind<\/li>\n <li><\/span>minister<\/li>\n <li><\/span>minus<\/li>\n <li><\/span>minute<\/li>\n <li><\/span>miss<\/li>\n <li><\/span>mister<\/li>\n <li><\/span>moment<\/li>\n <li><\/span>monday<\/li>\n <li><\/span>money<\/li>\n <li><\/span>month<\/li>\n <li><\/span>more<\/li>\n <li><\/span>morning<\/li>\n <li><\/span>most<\/li>\n <li><\/span>mother<\/li>\n <li><\/span>motion<\/li>\n <li><\/span>move<\/li>\n <li><\/span>mrs<\/li>\n <li><\/span>much<\/li>\n <li><\/span>music<\/li>\n <li><\/span>must<\/li>\n <li><\/span>name<\/li>\n <li><\/span>nation<\/li>\n <li><\/span>nature<\/li>\n <li><\/span>near<\/li>\n <li><\/span>necessary<\/li>\n <li><\/span>need<\/li>\n <li><\/span>never<\/li>\n <li><\/span>new<\/li>\n <li><\/span>news<\/li>\n <li><\/span>next<\/li>\n <li><\/span>nice<\/li>\n <li><\/span>night<\/li>\n <li><\/span>nine<\/li>\n <li><\/span>no<\/li>\n <li><\/span>non<\/li>\n <li><\/span>none<\/li>\n <li><\/span>normal<\/li>\n <li><\/span>north<\/li>\n <li><\/span>not<\/li>\n <li><\/span>note<\/li>\n <li><\/span>notice<\/li>\n <li><\/span>now<\/li>\n <li><\/span>number<\/li>\n <li><\/span>obvious<\/li>\n <li><\/span>occasion<\/li>\n <li><\/span>odd<\/li>\n <li><\/span>of<\/li>\n <li><\/span>off<\/li>\n <li><\/span>offer<\/li>\n <li><\/span>office<\/li>\n <li><\/span>often<\/li>\n <li><\/span>okay<\/li>\n <li><\/span>old<\/li>\n <li><\/span>on<\/li>\n <li><\/span>once<\/li>\n <li><\/span>one<\/li>\n <li><\/span>only<\/li>\n <li><\/span>open<\/li>\n <li><\/span>operate<\/li>\n <li><\/span>opportunity<\/li>\n <li><\/span>oppose<\/li>\n <li><\/span>or<\/li>\n <li><\/span>order<\/li>\n <li><\/span>organize<\/li>\n <li><\/span>original<\/li>\n <li><\/span>other<\/li>\n <li><\/span>otherwise<\/li>\n <li><\/span>ought<\/li>\n <li><\/span>out<\/li>\n <li><\/span>over<\/li>\n <li><\/span>own<\/li>\n <li><\/span>pack<\/li>\n <li><\/span>page<\/li>\n <li><\/span>paint<\/li>\n <li><\/span>pair<\/li>\n <li><\/span>paper<\/li>\n <li><\/span>paragraph<\/li>\n <li><\/span>pardon<\/li>\n <li><\/span>parent<\/li>\n <li><\/span>park<\/li>\n <li><\/span>part<\/li>\n <li><\/span>particular<\/li>\n <li><\/span>party<\/li>\n <li><\/span>pass<\/li>\n <li><\/span>past<\/li>\n <li><\/span>pay<\/li>\n <li><\/span>pence<\/li>\n <li><\/span>pension<\/li>\n <li><\/span>people<\/li>\n <li><\/span>per<\/li>\n <li><\/span>percent<\/li>\n <li><\/span>perfect<\/li>\n <li><\/span>perhaps<\/li>\n <li><\/span>period<\/li>\n <li><\/span>person<\/li>\n <li><\/span>photograph<\/li>\n <li><\/span>pick<\/li>\n <li><\/span>picture<\/li>\n <li><\/span>piece<\/li>\n <li><\/span>place<\/li>\n <li><\/span>plan<\/li>\n <li><\/span>play<\/li>\n <li><\/span>please<\/li>\n <li><\/span>plus<\/li>\n <li><\/span>point<\/li>\n <li><\/span>police<\/li>\n <li><\/span>policy<\/li>\n <li><\/span>politic<\/li>\n <li><\/span>poor<\/li>\n <li><\/span>position<\/li>\n <li><\/span>positive<\/li>\n <li><\/span>possible<\/li>\n <li><\/span>post<\/li>\n <li><\/span>pound<\/li>\n <li><\/span>power<\/li>\n <li><\/span>practise<\/li>\n <li><\/span>prepare<\/li>\n <li><\/span>present<\/li>\n <li><\/span>press<\/li>\n <li><\/span>pressure<\/li>\n <li><\/span>presume<\/li>\n <li><\/span>pretty<\/li>\n <li><\/span>previous<\/li>\n <li><\/span>price<\/li>\n <li><\/span>print<\/li>\n <li><\/span>private<\/li>\n <li><\/span>probable<\/li>\n <li><\/span>problem<\/li>\n <li><\/span>proceed<\/li>\n <li><\/span>process<\/li>\n <li><\/span>produce<\/li>\n <li><\/span>product<\/li>\n <li><\/span>programme<\/li>\n <li><\/span>project<\/li>\n <li><\/span>proper<\/li>\n <li><\/span>propose<\/li>\n <li><\/span>protect<\/li>\n <li><\/span>provide<\/li>\n <li><\/span>public<\/li>\n <li><\/span>pull<\/li>\n <li><\/span>purpose<\/li>\n <li><\/span>push<\/li>\n <li><\/span>put<\/li>\n <li><\/span>quality<\/li>\n <li><\/span>quarter<\/li>\n <li><\/span>question<\/li>\n <li><\/span>quick<\/li>\n <li><\/span>quid<\/li>\n <li><\/span>quiet<\/li>\n <li><\/span>quite<\/li>\n <li><\/span>radio<\/li>\n <li><\/span>rail<\/li>\n <li><\/span>raise<\/li>\n <li><\/span>range<\/li>\n <li><\/span>rate<\/li>\n <li><\/span>rather<\/li>\n <li><\/span>read<\/li>\n <li><\/span>ready<\/li>\n <li><\/span>real<\/li>\n <li><\/span>realise<\/li>\n <li><\/span>really<\/li>\n <li><\/span>reason<\/li>\n <li><\/span>receive<\/li>\n <li><\/span>recent<\/li>\n <li><\/span>reckon<\/li>\n <li><\/span>recognize<\/li>\n <li><\/span>recommend<\/li>\n <li><\/span>record<\/li>\n <li><\/span>red<\/li>\n <li><\/span>reduce<\/li>\n <li><\/span>refer<\/li>\n <li><\/span>regard<\/li>\n <li><\/span>region<\/li>\n <li><\/span>relation<\/li>\n <li><\/span>remember<\/li>\n <li><\/span>report<\/li>\n <li><\/span>represent<\/li>\n <li><\/span>require<\/li>\n <li><\/span>research<\/li>\n <li><\/span>resource<\/li>\n <li><\/span>respect<\/li>\n <li><\/span>responsible<\/li>\n <li><\/span>rest<\/li>\n <li><\/span>result<\/li>\n <li><\/span>return<\/li>\n <li><\/span>rid<\/li>\n <li><\/span>right<\/li>\n <li><\/span>ring<\/li>\n <li><\/span>rise<\/li>\n <li><\/span>road<\/li>\n <li><\/span>role<\/li>\n <li><\/span>roll<\/li>\n <li><\/span>room<\/li>\n <li><\/span>round<\/li>\n <li><\/span>rule<\/li>\n <li><\/span>run<\/li>\n <li><\/span>safe<\/li>\n <li><\/span>sale<\/li>\n <li><\/span>same<\/li>\n <li><\/span>saturday<\/li>\n <li><\/span>save<\/li>\n <li><\/span>say<\/li>\n <li><\/span>scheme<\/li>\n <li><\/span>school<\/li>\n <li><\/span>science<\/li>\n <li><\/span>score<\/li>\n <li><\/span>scotland<\/li>\n <li><\/span>seat<\/li>\n <li><\/span>second<\/li>\n <li><\/span>secretary<\/li>\n <li><\/span>section<\/li>\n <li><\/span>secure<\/li>\n <li><\/span>see<\/li>\n <li><\/span>seem<\/li>\n <li><\/span>self<\/li>\n <li><\/span>sell<\/li>\n <li><\/span>send<\/li>\n <li><\/span>sense<\/li>\n <li><\/span>separate<\/li>\n <li><\/span>serious<\/li>\n <li><\/span>serve<\/li>\n <li><\/span>service<\/li>\n <li><\/span>set<\/li>\n <li><\/span>settle<\/li>\n <li><\/span>seven<\/li>\n <li><\/span>sex<\/li>\n <li><\/span>shall<\/li>\n <li><\/span>share<\/li>\n <li><\/span>she<\/li>\n <li><\/span>sheet<\/li>\n <li><\/span>shoe<\/li>\n <li><\/span>shoot<\/li>\n <li><\/span>shop<\/li>\n <li><\/span>short<\/li>\n <li><\/span>should<\/li>\n <li><\/span>show<\/li>\n <li><\/span>shut<\/li>\n <li><\/span>sick<\/li>\n <li><\/span>side<\/li>\n <li><\/span>sign<\/li>\n <li><\/span>similar<\/li>\n <li><\/span>simple<\/li>\n <li><\/span>since<\/li>\n <li><\/span>sing<\/li>\n <li><\/span>single<\/li>\n <li><\/span>sir<\/li>\n <li><\/span>sister<\/li>\n <li><\/span>sit<\/li>\n <li><\/span>site<\/li>\n <li><\/span>situate<\/li>\n <li><\/span>six<\/li>\n <li><\/span>size<\/li>\n <li><\/span>sleep<\/li>\n <li><\/span>slight<\/li>\n <li><\/span>slow<\/li>\n <li><\/span>small<\/li>\n <li><\/span>smoke<\/li>\n <li><\/span>so<\/li>\n <li><\/span>social<\/li>\n <li><\/span>society<\/li>\n <li><\/span>some<\/li>\n <li><\/span>son<\/li>\n <li><\/span>soon<\/li>\n <li><\/span>sorry<\/li>\n <li><\/span>sort<\/li>\n <li><\/span>sound<\/li>\n <li><\/span>south<\/li>\n <li><\/span>space<\/li>\n <li><\/span>speak<\/li>\n <li><\/span>special<\/li>\n <li><\/span>specific<\/li>\n <li><\/span>speed<\/li>\n <li><\/span>spell<\/li>\n <li><\/span>spend<\/li>\n <li><\/span>square<\/li>\n <li><\/span>staff<\/li>\n <li><\/span>stage<\/li>\n <li><\/span>stairs<\/li>\n <li><\/span>stand<\/li>\n <li><\/span>standard<\/li>\n <li><\/span>start<\/li>\n <li><\/span>state<\/li>\n <li><\/span>station<\/li>\n <li><\/span>stay<\/li>\n <li><\/span>step<\/li>\n <li><\/span>stick<\/li>\n <li><\/span>still<\/li>\n <li><\/span>stop<\/li>\n <li><\/span>story<\/li>\n <li><\/span>straight<\/li>\n <li><\/span>strategy<\/li>\n <li><\/span>street<\/li>\n <li><\/span>strike<\/li>\n <li><\/span>strong<\/li>\n <li><\/span>structure<\/li>\n <li><\/span>student<\/li>\n <li><\/span>study<\/li>\n <li><\/span>stuff<\/li>\n <li><\/span>stupid<\/li>\n <li><\/span>subject<\/li>\n <li><\/span>succeed<\/li>\n <li><\/span>such<\/li>\n <li><\/span>sudden<\/li>\n <li><\/span>suggest<\/li>\n <li><\/span>suit<\/li>\n <li><\/span>summer<\/li>\n <li><\/span>sun<\/li>\n <li><\/span>sunday<\/li>\n <li><\/span>supply<\/li>\n <li><\/span>support<\/li>\n <li><\/span>suppose<\/li>\n <li><\/span>sure<\/li>\n <li><\/span>surprise<\/li>\n <li><\/span>switch<\/li>\n <li><\/span>system<\/li>\n <li><\/span>table<\/li>\n <li><\/span>take<\/li>\n <li><\/span>talk<\/li>\n <li><\/span>tape<\/li>\n <li><\/span>tax<\/li>\n <li><\/span>tea<\/li>\n <li><\/span>teach<\/li>\n <li><\/span>team<\/li>\n <li><\/span>telephone<\/li>\n <li><\/span>television<\/li>\n <li><\/span>tell<\/li>\n <li><\/span>ten<\/li>\n <li><\/span>tend<\/li>\n <li><\/span>term<\/li>\n <li><\/span>terrible<\/li>\n <li><\/span>test<\/li>\n <li><\/span>than<\/li>\n <li><\/span>thank<\/li>\n <li><\/span>the<\/li>\n <li><\/span>then<\/li>\n <li><\/span>there<\/li>\n <li><\/span>therefore<\/li>\n <li><\/span>they<\/li>\n <li><\/span>thing<\/li>\n <li><\/span>think<\/li>\n <li><\/span>thirteen<\/li>\n <li><\/span>thirty<\/li>\n <li><\/span>this<\/li>\n <li><\/span>thou<\/li>\n <li><\/span>though<\/li>\n <li><\/span>thousand<\/li>\n <li>thr<\/span>ee<\/li>\n <li>thr<\/span>ough<\/li>\n <li>thr<\/span>ow<\/li>\n <li><\/span>thursday<\/li>\n <li><\/span>tie<\/li>\n <li><\/span>time<\/li>\n <li><\/span>to<\/li>\n <li><\/span>today<\/li>\n <li><\/span>together<\/li>\n <li><\/span>tomorrow<\/li>\n <li><\/span>tonight<\/li>\n <li><\/span>too<\/li>\n <li><\/span>top<\/li>\n <li><\/span>total<\/li>\n <li><\/span>touch<\/li>\n <li><\/span>toward<\/li>\n <li><\/span>town<\/li>\n <li><\/span>trade<\/li>\n <li><\/span>traffic<\/li>\n <li><\/span>train<\/li>\n <li><\/span>transport<\/li>\n <li><\/span>travel<\/li>\n <li><\/span>treat<\/li>\n <li><\/span>tree<\/li>\n <li><\/span>trouble<\/li>\n <li><\/span>true<\/li>\n <li><\/span>trust<\/li>\n <li><\/span>try<\/li>\n <li><\/span>tuesday<\/li>\n <li><\/span>turn<\/li>\n <li><\/span>twelve<\/li>\n <li><\/span>twenty<\/li>\n <li><\/span>two<\/li>\n <li><\/span>type<\/li>\n <li><\/span>under<\/li>\n <li><\/span>understand<\/li>\n <li><\/span>union<\/li>\n <li><\/span>unit<\/li>\n <li><\/span>unite<\/li>\n <li><\/span>university<\/li>\n <li><\/span>unless<\/li>\n <li><\/span>until<\/li>\n <li><\/span>up<\/li>\n <li><\/span>upon<\/li>\n <li><\/span>use<\/li>\n <li><\/span>usual<\/li>\n <li><\/span>value<\/li>\n <li><\/span>various<\/li>\n <li><\/span>very<\/li>\n <li><\/span>video<\/li>\n <li><\/span>view<\/li>\n <li><\/span>village<\/li>\n <li><\/span>visit<\/li>\n <li><\/span>vote<\/li>\n <li><\/span>wage<\/li>\n <li><\/span>wait<\/li>\n <li><\/span>walk<\/li>\n <li><\/span>wall<\/li>\n <li><\/span>want<\/li>\n <li><\/span>war<\/li>\n <li><\/span>warm<\/li>\n <li><\/span>wash<\/li>\n <li><\/span>waste<\/li>\n <li><\/span>watch<\/li>\n <li><\/span>water<\/li>\n <li><\/span>way<\/li>\n <li><\/span>we<\/li>\n <li><\/span>wear<\/li>\n <li><\/span>wednesday<\/li>\n <li><\/span>wee<\/li>\n <li><\/span>week<\/li>\n <li><\/span>weigh<\/li>\n <li><\/span>welcome<\/li>\n <li><\/span>well<\/li>\n <li><\/span>west<\/li>\n <li><\/span>what<\/li>\n <li><\/span>when<\/li>\n <li><\/span>where<\/li>\n <li><\/span>whether<\/li>\n <li><\/span>which<\/li>\n <li><\/span>while<\/li>\n <li><\/span>white<\/li>\n <li><\/span>who<\/li>\n <li><\/span>whole<\/li>\n <li><\/span>why<\/li>\n <li><\/span>wide<\/li>\n <li><\/span>wife<\/li>\n <li><\/span>will<\/li>\n <li><\/span>win<\/li>\n <li><\/span>wind<\/li>\n <li><\/span>window<\/li>\n <li><\/span>wish<\/li>\n <li><\/span>with<\/li>\n <li><\/span>within<\/li>\n <li><\/span>without<\/li>\n <li><\/span>woman<\/li>\n <li><\/span>wonder<\/li>\n <li><\/span>wood<\/li>\n <li><\/span>word<\/li>\n <li><\/span>work<\/li>\n <li><\/span>world<\/li>\n <li><\/span>worry<\/li>\n <li><\/span>worse<\/li>\n <li><\/span>worth<\/li>\n <li><\/span>would<\/li>\n <li><\/span>write<\/li>\n <li><\/span>wrong<\/li>\n <li><\/span>year<\/li>\n <li><\/span>yes<\/li>\n <li><\/span>yesterday<\/li>\n <li><\/span>yet<\/li>\n <li><\/span>you<\/li>\n <li><\/span>young<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>

### Canonical principle #5: Quantifiers

+ `*`: matches at least 0 times.   
  + `+`: matches at least 1 times.     
  + `?`: matches at most 1 times.    
  + `{n}`: matches exactly n times.    
  + `{n,}`: matches at least n times.    
  + `{n,m}`: matches between n and m times.

```r
x <- c("dkl kls. klk. _", "(425) 591-6020", "her number is (581) 434-3242", "442", " dsi")
str_view(x, "^[dkh]*$")
```

<div id="htmlwidget-45ba7757ee08daea254a" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-45ba7757ee08daea254a">{"x":{"html":"<ul>\n <li>dkl kls. klk. _<\/li>\n <li>(425) 591-6020<\/li>\n <li>her number is (581) 434-3242<\/li>\n <li>442<\/li>\n <li> dsi<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>

---

```r
x <- c("123-456-7890", "(123)456-7890", "(123) 456-7890", "1235-2351")
str_view(x, "\$[0-9][0-9][0-9]\$[ ]*[0-9][0-9][0-9]-[0-9][0-9][0-9][0-9]")
```

<div id="htmlwidget-12abf83995d7e8fe16c1" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-12abf83995d7e8fe16c1">{"x":{"html":"<ul>\n <li>123-456-7890<\/li>\n <li>(123)456-7890<\/span><\/li>\n <li>(123) 456-7890<\/span><\/li>\n <li>1235-2351<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>

```r
x <- c("123-456-7890", "(123)456-7890", "(123) 456-7890", "1235-2351")
str_view(x, "\$[0-9][0-9][0-9]\$[ ]+[0-9][0-9][0-9]-[0-9][0-9][0-9][0-9]")
```

<div id="htmlwidget-ae32a8f0456fc88224bf" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-ae32a8f0456fc88224bf">{"x":{"html":"<ul>\n <li>123-456-7890<\/li>\n <li>(123)456-7890<\/li>\n <li>(123) 456-7890<\/span><\/li>\n <li>1235-2351<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>

---

```r
x <- c("123456-7890", "(123) 456-7890", "(123)456-7890", "1235-2351")
str_view(x, "\$[0-9][0-9][0-9]\$[ ]?[0-9][0-9][0-9]-[0-9][0-9][0-9][0-9]")
```

<div id="htmlwidget-535a60b5cdecdf9de9f5" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-535a60b5cdecdf9de9f5">{"x":{"html":"<ul>\n <li>123456-7890<\/li>\n <li>(123) 456-7890<\/span><\/li>\n <li>(123)456-7890<\/span><\/li>\n <li>1235-2351<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>
---

```r
x <- c("4444-22-22", "test", "333-4444-22")
str_view(x, "\\d{4}-\\d{2}-\\d{2}")
```

<div id="htmlwidget-bfe950301f6dcd10bd13" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-bfe950301f6dcd10bd13">{"x":{"html":"<ul>\n <li>4444-22-22<\/span><\/li>\n <li>test<\/li>\n <li>333-4444-22<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>

---

### Canonical principle #6: Character Clusters

```r
enron %>% filter(str_detect(email, "@.*\\.(edu|net)")) %>% select(email)
```

```
## # A tibble: 1,646 × 1
## email 
## <chr> 
## 1 "<retwell@mail.sanmarcos.net>" 
## 2 "cc: \"Larry Lewter\" <retwell@mail.sanmarcos.net>, \"Claudia L. Crocker\""
## 3 "\"Bob McKinney\" <capstone@texas.net> on 11/27/2000 09:46:13 AM" 
## 4 "To: \"Capstone\" <capstone@texas.net>" 
## 5 "Brian_Hoskins@enron.net" 
## 6 "Brian_Hoskins@enron.net" 
## 7 "Brian_Hoskins@enron.net" 
## 8 "Brian_Hoskins@enron.net" 
## 9 "To: adam.r.bayer@vanderbilt.edu" 
## 10 "X-To: \"Adam Bayer\" <adam.r.bayer@vanderbilt.edu> @ ENRON" 
## # … with 1,636 more rows
```

```r
enron %>% filter(str_detect(email, "@.*(ns)\\.(net)")) %>% select(email)
```

```
## # A tibble: 6 × 1
## email 
## <chr> 
## 1 "\"Karen Edson\" <kedson@ns.net> on 07/08/2000 03:06:40 PM" 
## 2 "cc: \"Julee Malinowski-Ball (E-mail)\" <jmball@ns.net>, \"Ray McNally (E-mai…
## 3 "kedson@ns.net" 
## 4 "<fotinb@bc-mail.com>; \"Bill Hannah\" <hannahs@wans.net>; \"Bill Harvey\"" 
## 5 "\"Harvey Wax\" <HLWAX@aol.com>; \"J. D Zikuda\" <jdzikuda@netins.net>; \"Jam…
## 6 "<rndyhbnr@midplains.net>; \"Ray Clary\" <rclrec@mindspring.com>; \"Rich Hari…
```
---

### Lets Play!

https://regexcrossword.com/challenges/beginner/puzzles/1

---

### Acknowledgements

Material has been borrowed heavily from the STAT 545 course. This course was started by Jenny Bryan: https://stat545.stat.ubc.ca/notes/notes-b05/

More STAT 545 resources: https://stat545.com/character-vectors.html, https://youtu.be/I0dJ1zpxAtU

R for Data Science chapter on Strings: https://r4ds.had.co.nz/strings.html

Solution set for R4DS on Strings: https://brshallo.github.io/r4ds_solutions/14-strings.html#matching-patterns-w-regex

Regex Puzzle Builder: https://regexcrossword.com/puzzlebuilder