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stringr.html
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stringr.html
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<h1 class="title toc-ignore">Introduction to stringr</h1>
<p>There are four main families of functions in stringr:</p>
<ol style="list-style-type: decimal">
<li><p>Character manipulation: these functions allow you to manipulate individual characters within the strings in character vectors.</p></li>
<li><p>Whitespace tools to add, remove, and manipulate whitespace.</p></li>
<li><p>Locale sensitive operations whose operations will vary from locale to locale.</p></li>
<li><p>Pattern matching functions. These recognise four engines of pattern description. The most common is regular expressions, but there are three other tools.</p></li>
</ol>
<div id="getting-and-setting-individual-characters" class="section level2">
<h2>Getting and setting individual characters</h2>
<p>You can get the length of the string with <code>str_length()</code>:</p>
<div class="sourceCode" id="cb1"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb1-1" data-line-number="1"><span class="kw">str_length</span>(<span class="st">"abc"</span>)</a>
<a class="sourceLine" id="cb1-2" data-line-number="2"><span class="co">#> [1] 3</span></a></code></pre></div>
<p>This is now equivalent to the base R function <code>nchar()</code>. Previously it was needed to work around issues with <code>nchar()</code> such as the fact that it returned 2 for <code>nchar(NA)</code>. This has been fixed as of R 3.3.0, so it is no longer so important.</p>
<p>You can access individual character using <code>str_sub()</code>. It takes three arguments: a character vector, a <code>start</code> position and an <code>end</code> position. Either position can either be a positive integer, which counts from the left, or a negative integer which counts from the right. The positions are inclusive, and if longer than the string, will be silently truncated.</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb2-1" data-line-number="1">x <-<span class="st"> </span><span class="kw">c</span>(<span class="st">"abcdef"</span>, <span class="st">"ghifjk"</span>)</a>
<a class="sourceLine" id="cb2-2" data-line-number="2"></a>
<a class="sourceLine" id="cb2-3" data-line-number="3"><span class="co"># The 3rd letter</span></a>
<a class="sourceLine" id="cb2-4" data-line-number="4"><span class="kw">str_sub</span>(x, <span class="dv">3</span>, <span class="dv">3</span>)</a>
<a class="sourceLine" id="cb2-5" data-line-number="5"><span class="co">#> [1] "c" "i"</span></a>
<a class="sourceLine" id="cb2-6" data-line-number="6"></a>
<a class="sourceLine" id="cb2-7" data-line-number="7"><span class="co"># The 2nd to 2nd-to-last character</span></a>
<a class="sourceLine" id="cb2-8" data-line-number="8"><span class="kw">str_sub</span>(x, <span class="dv">2</span>, <span class="dv">-2</span>)</a>
<a class="sourceLine" id="cb2-9" data-line-number="9"><span class="co">#> [1] "bcde" "hifj"</span></a></code></pre></div>
<p>You can also use <code>str_sub()</code> to modify strings:</p>
<div class="sourceCode" id="cb3"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb3-1" data-line-number="1"><span class="kw">str_sub</span>(x, <span class="dv">3</span>, <span class="dv">3</span>) <-<span class="st"> "X"</span></a>
<a class="sourceLine" id="cb3-2" data-line-number="2">x</a>
<a class="sourceLine" id="cb3-3" data-line-number="3"><span class="co">#> [1] "abXdef" "ghXfjk"</span></a></code></pre></div>
<p>To duplicate individual strings, you can use <code>str_dup()</code>:</p>
<div class="sourceCode" id="cb4"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb4-1" data-line-number="1"><span class="kw">str_dup</span>(x, <span class="kw">c</span>(<span class="dv">2</span>, <span class="dv">3</span>))</a>
<a class="sourceLine" id="cb4-2" data-line-number="2"><span class="co">#> [1] "abXdefabXdef" "ghXfjkghXfjkghXfjk"</span></a></code></pre></div>
</div>
<div id="whitespace" class="section level2">
<h2>Whitespace</h2>
<p>Three functions add, remove, or modify whitespace:</p>
<ol style="list-style-type: decimal">
<li><p><code>str_pad()</code> pads a string to a fixed length by adding extra whitespace on the left, right, or both sides.</p>
<div class="sourceCode" id="cb5"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb5-1" data-line-number="1">x <-<span class="st"> </span><span class="kw">c</span>(<span class="st">"abc"</span>, <span class="st">"defghi"</span>)</a>
<a class="sourceLine" id="cb5-2" data-line-number="2"><span class="kw">str_pad</span>(x, <span class="dv">10</span>) <span class="co"># default pads on left</span></a>
<a class="sourceLine" id="cb5-3" data-line-number="3"><span class="co">#> [1] " abc" " defghi"</span></a>
<a class="sourceLine" id="cb5-4" data-line-number="4"><span class="kw">str_pad</span>(x, <span class="dv">10</span>, <span class="st">"both"</span>)</a>
<a class="sourceLine" id="cb5-5" data-line-number="5"><span class="co">#> [1] " abc " " defghi "</span></a></code></pre></div>
<p>(You can pad with other characters by using the <code>pad</code> argument.)</p>
<p><code>str_pad()</code> will never make a string shorter:</p>
<div class="sourceCode" id="cb6"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb6-1" data-line-number="1"><span class="kw">str_pad</span>(x, <span class="dv">4</span>)</a>
<a class="sourceLine" id="cb6-2" data-line-number="2"><span class="co">#> [1] " abc" "defghi"</span></a></code></pre></div>
<p>So if you want to ensure that all strings are the same length (often useful for print methods), combine <code>str_pad()</code> and <code>str_trunc()</code>:</p>
<div class="sourceCode" id="cb7"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb7-1" data-line-number="1">x <-<span class="st"> </span><span class="kw">c</span>(<span class="st">"Short"</span>, <span class="st">"This is a long string"</span>)</a>
<a class="sourceLine" id="cb7-2" data-line-number="2"></a>
<a class="sourceLine" id="cb7-3" data-line-number="3">x <span class="op">%>%</span><span class="st"> </span></a>
<a class="sourceLine" id="cb7-4" data-line-number="4"><span class="st"> </span><span class="kw">str_trunc</span>(<span class="dv">10</span>) <span class="op">%>%</span><span class="st"> </span></a>
<a class="sourceLine" id="cb7-5" data-line-number="5"><span class="st"> </span><span class="kw">str_pad</span>(<span class="dv">10</span>, <span class="st">"right"</span>)</a>
<a class="sourceLine" id="cb7-6" data-line-number="6"><span class="co">#> [1] "Short " "This is..."</span></a></code></pre></div></li>
<li><p>The opposite of <code>str_pad()</code> is <code>str_trim()</code>, which removes leading and trailing whitespace:</p>
<div class="sourceCode" id="cb8"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb8-1" data-line-number="1">x <-<span class="st"> </span><span class="kw">c</span>(<span class="st">" a "</span>, <span class="st">"b "</span>, <span class="st">" c"</span>)</a>
<a class="sourceLine" id="cb8-2" data-line-number="2"><span class="kw">str_trim</span>(x)</a>
<a class="sourceLine" id="cb8-3" data-line-number="3"><span class="co">#> [1] "a" "b" "c"</span></a>
<a class="sourceLine" id="cb8-4" data-line-number="4"><span class="kw">str_trim</span>(x, <span class="st">"left"</span>)</a>
<a class="sourceLine" id="cb8-5" data-line-number="5"><span class="co">#> [1] "a " "b " "c"</span></a></code></pre></div></li>
<li><p>You can use <code>str_wrap()</code> to modify existing whitespace in order to wrap a paragraph of text, such that the length of each line is as similar as possible.</p>
<div class="sourceCode" id="cb9"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb9-1" data-line-number="1">jabberwocky <-<span class="st"> </span><span class="kw">str_c</span>(</a>
<a class="sourceLine" id="cb9-2" data-line-number="2"> <span class="st">"`Twas brillig, and the slithy toves "</span>,</a>
<a class="sourceLine" id="cb9-3" data-line-number="3"> <span class="st">"did gyre and gimble in the wabe: "</span>,</a>
<a class="sourceLine" id="cb9-4" data-line-number="4"> <span class="st">"All mimsy were the borogoves, "</span>,</a>
<a class="sourceLine" id="cb9-5" data-line-number="5"> <span class="st">"and the mome raths outgrabe. "</span></a>
<a class="sourceLine" id="cb9-6" data-line-number="6">)</a>
<a class="sourceLine" id="cb9-7" data-line-number="7"><span class="kw">cat</span>(<span class="kw">str_wrap</span>(jabberwocky, <span class="dt">width =</span> <span class="dv">40</span>))</a>
<a class="sourceLine" id="cb9-8" data-line-number="8"><span class="co">#> `Twas brillig, and the slithy toves did</span></a>
<a class="sourceLine" id="cb9-9" data-line-number="9"><span class="co">#> gyre and gimble in the wabe: All mimsy</span></a>
<a class="sourceLine" id="cb9-10" data-line-number="10"><span class="co">#> were the borogoves, and the mome raths</span></a>
<a class="sourceLine" id="cb9-11" data-line-number="11"><span class="co">#> outgrabe.</span></a></code></pre></div></li>
</ol>
</div>
<div id="locale-sensitive" class="section level2">
<h2>Locale sensitive</h2>
<p>A handful of stringr functions are locale-sensitive: they will perform differently in different regions of the world. These functions are case transformation functions:</p>
<div class="sourceCode" id="cb10"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb10-1" data-line-number="1">x <-<span class="st"> "I like horses."</span></a>
<a class="sourceLine" id="cb10-2" data-line-number="2"><span class="kw">str_to_upper</span>(x)</a>
<a class="sourceLine" id="cb10-3" data-line-number="3"><span class="co">#> [1] "I LIKE HORSES."</span></a>
<a class="sourceLine" id="cb10-4" data-line-number="4"><span class="kw">str_to_title</span>(x)</a>
<a class="sourceLine" id="cb10-5" data-line-number="5"><span class="co">#> [1] "I Like Horses."</span></a>
<a class="sourceLine" id="cb10-6" data-line-number="6"></a>
<a class="sourceLine" id="cb10-7" data-line-number="7"><span class="kw">str_to_lower</span>(x)</a>
<a class="sourceLine" id="cb10-8" data-line-number="8"><span class="co">#> [1] "i like horses."</span></a>
<a class="sourceLine" id="cb10-9" data-line-number="9"><span class="co"># Turkish has two sorts of i: with and without the dot</span></a>
<a class="sourceLine" id="cb10-10" data-line-number="10"><span class="kw">str_to_lower</span>(x, <span class="st">"tr"</span>)</a>
<a class="sourceLine" id="cb10-11" data-line-number="11"><span class="co">#> [1] "ı like horses."</span></a></code></pre></div>
<p>String ordering and sorting:</p>
<div class="sourceCode" id="cb11"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb11-1" data-line-number="1">x <-<span class="st"> </span><span class="kw">c</span>(<span class="st">"y"</span>, <span class="st">"i"</span>, <span class="st">"k"</span>)</a>
<a class="sourceLine" id="cb11-2" data-line-number="2"><span class="kw">str_order</span>(x)</a>
<a class="sourceLine" id="cb11-3" data-line-number="3"><span class="co">#> [1] 2 3 1</span></a>
<a class="sourceLine" id="cb11-4" data-line-number="4"></a>
<a class="sourceLine" id="cb11-5" data-line-number="5"><span class="kw">str_sort</span>(x)</a>
<a class="sourceLine" id="cb11-6" data-line-number="6"><span class="co">#> [1] "i" "k" "y"</span></a>
<a class="sourceLine" id="cb11-7" data-line-number="7"><span class="co"># In Lithuanian, y comes between i and k</span></a>
<a class="sourceLine" id="cb11-8" data-line-number="8"><span class="kw">str_sort</span>(x, <span class="dt">locale =</span> <span class="st">"lt"</span>)</a>
<a class="sourceLine" id="cb11-9" data-line-number="9"><span class="co">#> [1] "i" "y" "k"</span></a></code></pre></div>
<p>The locale always defaults to English to ensure that the default behaviour is identical across systems. Locales always include a two letter ISO-639-1 language code (like “en” for English or “zh” for Chinese), and optionally a ISO-3166 country code (like “en_UK” vs “en_US”). You can see a complete list of available locales by running <code>stringi::stri_locale_list()</code>.</p>
</div>
<div id="pattern-matching" class="section level2">
<h2>Pattern matching</h2>
<p>The vast majority of stringr functions work with patterns. These are parameterised by the task they perform and the types of patterns they match.</p>
<div id="tasks" class="section level3">
<h3>Tasks</h3>
<p>Each pattern matching function has the same first two arguments, a character vector of <code>string</code>s to process and a single <code>pattern</code> to match. stringr provides pattern matching functions to <strong>detect</strong>, <strong>locate</strong>, <strong>extract</strong>, <strong>match</strong>, <strong>replace</strong>, and <strong>split</strong> strings. I’ll illustrate how they work with some strings and a regular expression designed to match (US) phone numbers:</p>
<div class="sourceCode" id="cb12"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb12-1" data-line-number="1">strings <-<span class="st"> </span><span class="kw">c</span>(</a>
<a class="sourceLine" id="cb12-2" data-line-number="2"> <span class="st">"apple"</span>, </a>
<a class="sourceLine" id="cb12-3" data-line-number="3"> <span class="st">"219 733 8965"</span>, </a>
<a class="sourceLine" id="cb12-4" data-line-number="4"> <span class="st">"329-293-8753"</span>, </a>
<a class="sourceLine" id="cb12-5" data-line-number="5"> <span class="st">"Work: 579-499-7527; Home: 543.355.3679"</span></a>
<a class="sourceLine" id="cb12-6" data-line-number="6">)</a>
<a class="sourceLine" id="cb12-7" data-line-number="7">phone <-<span class="st"> "([2-9][0-9]{2})[- .]([0-9]{3})[- .]([0-9]{4})"</span></a></code></pre></div>
<ul>
<li><p><code>str_detect()</code> detects the presence or absence of a pattern and returns a logical vector (similar to <code>grepl()</code>). <code>str_subset()</code> returns the elements of a character vector that match a regular expression (similar to <code>grep()</code> with <code>value = TRUE</code>)`.</p>
<div class="sourceCode" id="cb13"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb13-1" data-line-number="1"><span class="co"># Which strings contain phone numbers?</span></a>
<a class="sourceLine" id="cb13-2" data-line-number="2"><span class="kw">str_detect</span>(strings, phone)</a>
<a class="sourceLine" id="cb13-3" data-line-number="3"><span class="co">#> [1] FALSE TRUE TRUE TRUE</span></a>
<a class="sourceLine" id="cb13-4" data-line-number="4"><span class="kw">str_subset</span>(strings, phone)</a>
<a class="sourceLine" id="cb13-5" data-line-number="5"><span class="co">#> [1] "219 733 8965" </span></a>
<a class="sourceLine" id="cb13-6" data-line-number="6"><span class="co">#> [2] "329-293-8753" </span></a>
<a class="sourceLine" id="cb13-7" data-line-number="7"><span class="co">#> [3] "Work: 579-499-7527; Home: 543.355.3679"</span></a></code></pre></div></li>
<li><p><code>str_count()</code> counts the number of matches:</p>
<div class="sourceCode" id="cb14"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb14-1" data-line-number="1"><span class="co"># How many phone numbers in each string?</span></a>
<a class="sourceLine" id="cb14-2" data-line-number="2"><span class="kw">str_count</span>(strings, phone)</a>
<a class="sourceLine" id="cb14-3" data-line-number="3"><span class="co">#> [1] 0 1 1 2</span></a></code></pre></div></li>
<li><p><code>str_locate()</code> locates the <strong>first</strong> position of a pattern and returns a numeric matrix with columns start and end. <code>str_locate_all()</code> locates all matches, returning a list of numeric matrices. Similar to <code>regexpr()</code> and <code>gregexpr()</code>.</p>
<div class="sourceCode" id="cb15"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb15-1" data-line-number="1"><span class="co"># Where in the string is the phone number located?</span></a>
<a class="sourceLine" id="cb15-2" data-line-number="2">(loc <-<span class="st"> </span><span class="kw">str_locate</span>(strings, phone))</a>
<a class="sourceLine" id="cb15-3" data-line-number="3"><span class="co">#> start end</span></a>
<a class="sourceLine" id="cb15-4" data-line-number="4"><span class="co">#> [1,] NA NA</span></a>
<a class="sourceLine" id="cb15-5" data-line-number="5"><span class="co">#> [2,] 1 12</span></a>
<a class="sourceLine" id="cb15-6" data-line-number="6"><span class="co">#> [3,] 1 12</span></a>
<a class="sourceLine" id="cb15-7" data-line-number="7"><span class="co">#> [4,] 7 18</span></a>
<a class="sourceLine" id="cb15-8" data-line-number="8"><span class="kw">str_locate_all</span>(strings, phone)</a>
<a class="sourceLine" id="cb15-9" data-line-number="9"><span class="co">#> [[1]]</span></a>
<a class="sourceLine" id="cb15-10" data-line-number="10"><span class="co">#> start end</span></a>
<a class="sourceLine" id="cb15-11" data-line-number="11"><span class="co">#> </span></a>
<a class="sourceLine" id="cb15-12" data-line-number="12"><span class="co">#> [[2]]</span></a>
<a class="sourceLine" id="cb15-13" data-line-number="13"><span class="co">#> start end</span></a>
<a class="sourceLine" id="cb15-14" data-line-number="14"><span class="co">#> [1,] 1 12</span></a>
<a class="sourceLine" id="cb15-15" data-line-number="15"><span class="co">#> </span></a>
<a class="sourceLine" id="cb15-16" data-line-number="16"><span class="co">#> [[3]]</span></a>
<a class="sourceLine" id="cb15-17" data-line-number="17"><span class="co">#> start end</span></a>
<a class="sourceLine" id="cb15-18" data-line-number="18"><span class="co">#> [1,] 1 12</span></a>
<a class="sourceLine" id="cb15-19" data-line-number="19"><span class="co">#> </span></a>
<a class="sourceLine" id="cb15-20" data-line-number="20"><span class="co">#> [[4]]</span></a>
<a class="sourceLine" id="cb15-21" data-line-number="21"><span class="co">#> start end</span></a>
<a class="sourceLine" id="cb15-22" data-line-number="22"><span class="co">#> [1,] 7 18</span></a>
<a class="sourceLine" id="cb15-23" data-line-number="23"><span class="co">#> [2,] 27 38</span></a></code></pre></div></li>
<li><p><code>str_extract()</code> extracts text corresponding to the <strong>first</strong> match, returning a character vector. <code>str_extract_all()</code> extracts all matches and returns a list of character vectors.</p>
<div class="sourceCode" id="cb16"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb16-1" data-line-number="1"><span class="co"># What are the phone numbers?</span></a>
<a class="sourceLine" id="cb16-2" data-line-number="2"><span class="kw">str_extract</span>(strings, phone)</a>
<a class="sourceLine" id="cb16-3" data-line-number="3"><span class="co">#> [1] NA "219 733 8965" "329-293-8753" "579-499-7527"</span></a>
<a class="sourceLine" id="cb16-4" data-line-number="4"><span class="kw">str_extract_all</span>(strings, phone)</a>
<a class="sourceLine" id="cb16-5" data-line-number="5"><span class="co">#> [[1]]</span></a>
<a class="sourceLine" id="cb16-6" data-line-number="6"><span class="co">#> character(0)</span></a>
<a class="sourceLine" id="cb16-7" data-line-number="7"><span class="co">#> </span></a>
<a class="sourceLine" id="cb16-8" data-line-number="8"><span class="co">#> [[2]]</span></a>
<a class="sourceLine" id="cb16-9" data-line-number="9"><span class="co">#> [1] "219 733 8965"</span></a>
<a class="sourceLine" id="cb16-10" data-line-number="10"><span class="co">#> </span></a>
<a class="sourceLine" id="cb16-11" data-line-number="11"><span class="co">#> [[3]]</span></a>
<a class="sourceLine" id="cb16-12" data-line-number="12"><span class="co">#> [1] "329-293-8753"</span></a>
<a class="sourceLine" id="cb16-13" data-line-number="13"><span class="co">#> </span></a>
<a class="sourceLine" id="cb16-14" data-line-number="14"><span class="co">#> [[4]]</span></a>
<a class="sourceLine" id="cb16-15" data-line-number="15"><span class="co">#> [1] "579-499-7527" "543.355.3679"</span></a>
<a class="sourceLine" id="cb16-16" data-line-number="16"><span class="kw">str_extract_all</span>(strings, phone, <span class="dt">simplify =</span> <span class="ot">TRUE</span>)</a>
<a class="sourceLine" id="cb16-17" data-line-number="17"><span class="co">#> [,1] [,2] </span></a>
<a class="sourceLine" id="cb16-18" data-line-number="18"><span class="co">#> [1,] "" "" </span></a>
<a class="sourceLine" id="cb16-19" data-line-number="19"><span class="co">#> [2,] "219 733 8965" "" </span></a>
<a class="sourceLine" id="cb16-20" data-line-number="20"><span class="co">#> [3,] "329-293-8753" "" </span></a>
<a class="sourceLine" id="cb16-21" data-line-number="21"><span class="co">#> [4,] "579-499-7527" "543.355.3679"</span></a></code></pre></div></li>
<li><p><code>str_match()</code> extracts capture groups formed by <code>()</code> from the <strong>first</strong> match. It returns a character matrix with one column for the complete match and one column for each group. <code>str_match_all()</code> extracts capture groups from all matches and returns a list of character matrices. Similar to <code>regmatches()</code>.</p>
<div class="sourceCode" id="cb17"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb17-1" data-line-number="1"><span class="co"># Pull out the three components of the match</span></a>
<a class="sourceLine" id="cb17-2" data-line-number="2"><span class="kw">str_match</span>(strings, phone)</a>
<a class="sourceLine" id="cb17-3" data-line-number="3"><span class="co">#> [,1] [,2] [,3] [,4] </span></a>
<a class="sourceLine" id="cb17-4" data-line-number="4"><span class="co">#> [1,] NA NA NA NA </span></a>
<a class="sourceLine" id="cb17-5" data-line-number="5"><span class="co">#> [2,] "219 733 8965" "219" "733" "8965"</span></a>
<a class="sourceLine" id="cb17-6" data-line-number="6"><span class="co">#> [3,] "329-293-8753" "329" "293" "8753"</span></a>
<a class="sourceLine" id="cb17-7" data-line-number="7"><span class="co">#> [4,] "579-499-7527" "579" "499" "7527"</span></a>
<a class="sourceLine" id="cb17-8" data-line-number="8"><span class="kw">str_match_all</span>(strings, phone)</a>
<a class="sourceLine" id="cb17-9" data-line-number="9"><span class="co">#> [[1]]</span></a>
<a class="sourceLine" id="cb17-10" data-line-number="10"><span class="co">#> [,1] [,2] [,3] [,4]</span></a>
<a class="sourceLine" id="cb17-11" data-line-number="11"><span class="co">#> </span></a>
<a class="sourceLine" id="cb17-12" data-line-number="12"><span class="co">#> [[2]]</span></a>
<a class="sourceLine" id="cb17-13" data-line-number="13"><span class="co">#> [,1] [,2] [,3] [,4] </span></a>
<a class="sourceLine" id="cb17-14" data-line-number="14"><span class="co">#> [1,] "219 733 8965" "219" "733" "8965"</span></a>
<a class="sourceLine" id="cb17-15" data-line-number="15"><span class="co">#> </span></a>
<a class="sourceLine" id="cb17-16" data-line-number="16"><span class="co">#> [[3]]</span></a>
<a class="sourceLine" id="cb17-17" data-line-number="17"><span class="co">#> [,1] [,2] [,3] [,4] </span></a>
<a class="sourceLine" id="cb17-18" data-line-number="18"><span class="co">#> [1,] "329-293-8753" "329" "293" "8753"</span></a>
<a class="sourceLine" id="cb17-19" data-line-number="19"><span class="co">#> </span></a>
<a class="sourceLine" id="cb17-20" data-line-number="20"><span class="co">#> [[4]]</span></a>
<a class="sourceLine" id="cb17-21" data-line-number="21"><span class="co">#> [,1] [,2] [,3] [,4] </span></a>
<a class="sourceLine" id="cb17-22" data-line-number="22"><span class="co">#> [1,] "579-499-7527" "579" "499" "7527"</span></a>
<a class="sourceLine" id="cb17-23" data-line-number="23"><span class="co">#> [2,] "543.355.3679" "543" "355" "3679"</span></a></code></pre></div></li>
<li><p><code>str_replace()</code> replaces the <strong>first</strong> matched pattern and returns a character vector. <code>str_replace_all()</code> replaces all matches. Similar to <code>sub()</code> and <code>gsub()</code>.</p>
<div class="sourceCode" id="cb18"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb18-1" data-line-number="1"><span class="kw">str_replace</span>(strings, phone, <span class="st">"XXX-XXX-XXXX"</span>)</a>
<a class="sourceLine" id="cb18-2" data-line-number="2"><span class="co">#> [1] "apple" </span></a>
<a class="sourceLine" id="cb18-3" data-line-number="3"><span class="co">#> [2] "XXX-XXX-XXXX" </span></a>
<a class="sourceLine" id="cb18-4" data-line-number="4"><span class="co">#> [3] "XXX-XXX-XXXX" </span></a>
<a class="sourceLine" id="cb18-5" data-line-number="5"><span class="co">#> [4] "Work: XXX-XXX-XXXX; Home: 543.355.3679"</span></a>
<a class="sourceLine" id="cb18-6" data-line-number="6"><span class="kw">str_replace_all</span>(strings, phone, <span class="st">"XXX-XXX-XXXX"</span>)</a>
<a class="sourceLine" id="cb18-7" data-line-number="7"><span class="co">#> [1] "apple" </span></a>
<a class="sourceLine" id="cb18-8" data-line-number="8"><span class="co">#> [2] "XXX-XXX-XXXX" </span></a>
<a class="sourceLine" id="cb18-9" data-line-number="9"><span class="co">#> [3] "XXX-XXX-XXXX" </span></a>
<a class="sourceLine" id="cb18-10" data-line-number="10"><span class="co">#> [4] "Work: XXX-XXX-XXXX; Home: XXX-XXX-XXXX"</span></a></code></pre></div></li>
<li><p><code>str_split_fixed()</code> splits a string into a <strong>fixed</strong> number of pieces based on a pattern and returns a character matrix. <code>str_split()</code> splits a string into a <strong>variable</strong> number of pieces and returns a list of character vectors.</p>
<div class="sourceCode" id="cb19"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb19-1" data-line-number="1"><span class="kw">str_split</span>(<span class="st">"a-b-c"</span>, <span class="st">"-"</span>)</a>
<a class="sourceLine" id="cb19-2" data-line-number="2"><span class="co">#> [[1]]</span></a>
<a class="sourceLine" id="cb19-3" data-line-number="3"><span class="co">#> [1] "a" "b" "c"</span></a>
<a class="sourceLine" id="cb19-4" data-line-number="4"><span class="kw">str_split_fixed</span>(<span class="st">"a-b-c"</span>, <span class="st">"-"</span>, <span class="dt">n =</span> <span class="dv">2</span>)</a>
<a class="sourceLine" id="cb19-5" data-line-number="5"><span class="co">#> [,1] [,2] </span></a>
<a class="sourceLine" id="cb19-6" data-line-number="6"><span class="co">#> [1,] "a" "b-c"</span></a></code></pre></div></li>
</ul>
</div>
<div id="engines" class="section level3">
<h3>Engines</h3>
<p>There are four main engines that stringr can use to describe patterns:</p>
<ul>
<li><p>Regular expressions, the default, as shown above, and described in <code>vignette("regular-expressions")</code>.</p></li>
<li><p>Fixed bytewise matching, with <code>fixed()</code>.</p></li>
<li><p>Locale-sensitive character matching, with <code>coll()</code></p></li>
<li><p>Text boundary analysis with <code>boundary()</code>.</p></li>
</ul>
<div id="fixed-matches" class="section level4">
<h4>Fixed matches</h4>
<p><code>fixed(x)</code> only matches the exact sequence of bytes specified by <code>x</code>. This is a very limited “pattern”, but the restriction can make matching much faster. Beware using <code>fixed()</code> with non-English data. It is problematic because there are often multiple ways of representing the same character. For example, there are two ways to define “á”: either as a single character or as an “a” plus an accent:</p>
<div class="sourceCode" id="cb20"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb20-1" data-line-number="1">a1 <-<span class="st"> "\u00e1"</span></a>
<a class="sourceLine" id="cb20-2" data-line-number="2">a2 <-<span class="st"> "a\u0301"</span></a>
<a class="sourceLine" id="cb20-3" data-line-number="3"><span class="kw">c</span>(a1, a2)</a>
<a class="sourceLine" id="cb20-4" data-line-number="4"><span class="co">#> [1] "á" "á"</span></a>
<a class="sourceLine" id="cb20-5" data-line-number="5">a1 <span class="op">==</span><span class="st"> </span>a2</a>
<a class="sourceLine" id="cb20-6" data-line-number="6"><span class="co">#> [1] FALSE</span></a></code></pre></div>
<p>They render identically, but because they’re defined differently, <code>fixed()</code> doesn’t find a match. Instead, you can use <code>coll()</code>, explained below, to respect human character comparison rules:</p>
<div class="sourceCode" id="cb21"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb21-1" data-line-number="1"><span class="kw">str_detect</span>(a1, <span class="kw">fixed</span>(a2))</a>
<a class="sourceLine" id="cb21-2" data-line-number="2"><span class="co">#> [1] FALSE</span></a>
<a class="sourceLine" id="cb21-3" data-line-number="3"><span class="kw">str_detect</span>(a1, <span class="kw">coll</span>(a2))</a>
<a class="sourceLine" id="cb21-4" data-line-number="4"><span class="co">#> [1] TRUE</span></a></code></pre></div>
</div>
<div id="collation-search" class="section level4">
<h4>Collation search</h4>
<p><code>coll(x)</code> looks for a match to <code>x</code> using human-language <strong>coll</strong>ation rules, and is particularly important if you want to do case insensitive matching. Collation rules differ around the world, so you’ll also need to supply a <code>locale</code> parameter.</p>
<div class="sourceCode" id="cb22"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb22-1" data-line-number="1">i <-<span class="st"> </span><span class="kw">c</span>(<span class="st">"I"</span>, <span class="st">"İ"</span>, <span class="st">"i"</span>, <span class="st">"ı"</span>)</a>
<a class="sourceLine" id="cb22-2" data-line-number="2">i</a>
<a class="sourceLine" id="cb22-3" data-line-number="3"><span class="co">#> [1] "I" "İ" "i" "ı"</span></a>
<a class="sourceLine" id="cb22-4" data-line-number="4"></a>
<a class="sourceLine" id="cb22-5" data-line-number="5"><span class="kw">str_subset</span>(i, <span class="kw">coll</span>(<span class="st">"i"</span>, <span class="dt">ignore_case =</span> <span class="ot">TRUE</span>))</a>
<a class="sourceLine" id="cb22-6" data-line-number="6"><span class="co">#> [1] "I" "i"</span></a>
<a class="sourceLine" id="cb22-7" data-line-number="7"><span class="kw">str_subset</span>(i, <span class="kw">coll</span>(<span class="st">"i"</span>, <span class="dt">ignore_case =</span> <span class="ot">TRUE</span>, <span class="dt">locale =</span> <span class="st">"tr"</span>))</a>
<a class="sourceLine" id="cb22-8" data-line-number="8"><span class="co">#> [1] "İ" "i"</span></a></code></pre></div>
<p>The downside of <code>coll()</code> is speed. Because the rules for recognising which characters are the same are complicated, <code>coll()</code> is relatively slow compared to <code>regex()</code> and <code>fixed()</code>. Note that when both <code>fixed()</code> and <code>regex()</code> have <code>ignore_case</code> arguments, they perform a much simpler comparison than <code>coll()</code>.</p>
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<div id="boundary" class="section level4">
<h4>Boundary</h4>
<p><code>boundary()</code> matches boundaries between characters, lines, sentences or words. It’s most useful with <code>str_split()</code>, but can be used with all pattern matching functions:</p>
<div class="sourceCode" id="cb23"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb23-1" data-line-number="1">x <-<span class="st"> "This is a sentence."</span></a>
<a class="sourceLine" id="cb23-2" data-line-number="2"><span class="kw">str_split</span>(x, <span class="kw">boundary</span>(<span class="st">"word"</span>))</a>
<a class="sourceLine" id="cb23-3" data-line-number="3"><span class="co">#> [[1]]</span></a>
<a class="sourceLine" id="cb23-4" data-line-number="4"><span class="co">#> [1] "This" "is" "a" "sentence"</span></a>
<a class="sourceLine" id="cb23-5" data-line-number="5"><span class="kw">str_count</span>(x, <span class="kw">boundary</span>(<span class="st">"word"</span>))</a>
<a class="sourceLine" id="cb23-6" data-line-number="6"><span class="co">#> [1] 4</span></a>
<a class="sourceLine" id="cb23-7" data-line-number="7"><span class="kw">str_extract_all</span>(x, <span class="kw">boundary</span>(<span class="st">"word"</span>))</a>
<a class="sourceLine" id="cb23-8" data-line-number="8"><span class="co">#> [[1]]</span></a>
<a class="sourceLine" id="cb23-9" data-line-number="9"><span class="co">#> [1] "This" "is" "a" "sentence"</span></a></code></pre></div>
<p>By convention, <code>""</code> is treated as <code>boundary("character")</code>:</p>
<div class="sourceCode" id="cb24"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb24-1" data-line-number="1"><span class="kw">str_split</span>(x, <span class="st">""</span>)</a>
<a class="sourceLine" id="cb24-2" data-line-number="2"><span class="co">#> [[1]]</span></a>
<a class="sourceLine" id="cb24-3" data-line-number="3"><span class="co">#> [1] "T" "h" "i" "s" " " "i" "s" " " "a" " " "s" "e" "n" "t" "e" "n" "c"</span></a>
<a class="sourceLine" id="cb24-4" data-line-number="4"><span class="co">#> [18] "e" "."</span></a>
<a class="sourceLine" id="cb24-5" data-line-number="5"><span class="kw">str_count</span>(x, <span class="st">""</span>)</a>
<a class="sourceLine" id="cb24-6" data-line-number="6"><span class="co">#> [1] 19</span></a></code></pre></div>
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