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<body>
<h1 class="title toc-ignore">The Text Interchange Formats and the
tokenizers Package</h1>
<h4 class="author">Lincoln Mullen</h4>
<p>The <a href="https://github.com/ropenscilabs/tif">Text Interchange
Formats</a> are a set of standards defined at an <a href="https://ropensci.org/">rOpenSci</a> sponsored <a href="https://textworkshop17.ropensci.org/">meeting in London</a> in
2017. The formats allow R text analysis packages to target defined
inputs and outputs for corpora, tokens, and document-term matrices. By
adhering to these recommendations, R packages can buy into an
interoperable ecosystem.</p>
<p>The TIF recommendations are still a draft, but the tokenizers package
implements its recommendation to accept both of the corpora formats and
to output one of its recommended tokens formats.</p>
<p>Consider these two recommended forms of a corpus. One
(<code>corpus_c</code>) is a named character vector; the other
(<code>corpus_d</code>) is a data frame. They both include a document ID
and the full text for each item. The data frame format obviously allows
for the use of other metadata fields besides the document ID, whereas
the other format does not. Using the coercion functions in the tif
package, one could switch back and forth between these formats.
Tokenizers also supports a corpus formatted as a named list where each
element is a character vector of length one (<code>corpus_l</code>),
though this is not a part of the draft TIF standards.</p>
<div class="sourceCode" id="cb1"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="co"># Named list</span></span>
<span id="cb1-2"><a href="#cb1-2" aria-hidden="true" tabindex="-1"></a>(corpus_l <span class="ot"><-</span> <span class="fu">list</span>(<span class="at">man_comes_around =</span> <span class="st">"There's a man goin' 'round takin' names"</span>,</span>
<span id="cb1-3"><a href="#cb1-3" aria-hidden="true" tabindex="-1"></a> <span class="at">wont_back_down =</span> <span class="st">"Well I won't back down, no I won't back down"</span>,</span>
<span id="cb1-4"><a href="#cb1-4" aria-hidden="true" tabindex="-1"></a> <span class="at">bird_on_a_wire =</span> <span class="st">"Like a bird on a wire"</span>))</span>
<span id="cb1-5"><a href="#cb1-5" aria-hidden="true" tabindex="-1"></a><span class="co">#> $man_comes_around</span></span>
<span id="cb1-6"><a href="#cb1-6" aria-hidden="true" tabindex="-1"></a><span class="co">#> [1] "There's a man goin' 'round takin' names"</span></span>
<span id="cb1-7"><a href="#cb1-7" aria-hidden="true" tabindex="-1"></a><span class="co">#> </span></span>
<span id="cb1-8"><a href="#cb1-8" aria-hidden="true" tabindex="-1"></a><span class="co">#> $wont_back_down</span></span>
<span id="cb1-9"><a href="#cb1-9" aria-hidden="true" tabindex="-1"></a><span class="co">#> [1] "Well I won't back down, no I won't back down"</span></span>
<span id="cb1-10"><a href="#cb1-10" aria-hidden="true" tabindex="-1"></a><span class="co">#> </span></span>
<span id="cb1-11"><a href="#cb1-11" aria-hidden="true" tabindex="-1"></a><span class="co">#> $bird_on_a_wire</span></span>
<span id="cb1-12"><a href="#cb1-12" aria-hidden="true" tabindex="-1"></a><span class="co">#> [1] "Like a bird on a wire"</span></span>
<span id="cb1-13"><a href="#cb1-13" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb1-14"><a href="#cb1-14" aria-hidden="true" tabindex="-1"></a><span class="co"># Named character vector</span></span>
<span id="cb1-15"><a href="#cb1-15" aria-hidden="true" tabindex="-1"></a>(corpus_c <span class="ot"><-</span> <span class="fu">unlist</span>(corpus_l))</span>
<span id="cb1-16"><a href="#cb1-16" aria-hidden="true" tabindex="-1"></a><span class="co">#> man_comes_around </span></span>
<span id="cb1-17"><a href="#cb1-17" aria-hidden="true" tabindex="-1"></a><span class="co">#> "There's a man goin' 'round takin' names" </span></span>
<span id="cb1-18"><a href="#cb1-18" aria-hidden="true" tabindex="-1"></a><span class="co">#> wont_back_down </span></span>
<span id="cb1-19"><a href="#cb1-19" aria-hidden="true" tabindex="-1"></a><span class="co">#> "Well I won't back down, no I won't back down" </span></span>
<span id="cb1-20"><a href="#cb1-20" aria-hidden="true" tabindex="-1"></a><span class="co">#> bird_on_a_wire </span></span>
<span id="cb1-21"><a href="#cb1-21" aria-hidden="true" tabindex="-1"></a><span class="co">#> "Like a bird on a wire"</span></span>
<span id="cb1-22"><a href="#cb1-22" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb1-23"><a href="#cb1-23" aria-hidden="true" tabindex="-1"></a><span class="co"># Data frame</span></span>
<span id="cb1-24"><a href="#cb1-24" aria-hidden="true" tabindex="-1"></a>(corpus_d <span class="ot"><-</span> <span class="fu">data.frame</span>(<span class="at">doc_id =</span> <span class="fu">names</span>(corpus_c), <span class="at">text =</span> <span class="fu">unname</span>(corpus_c),</span>
<span id="cb1-25"><a href="#cb1-25" aria-hidden="true" tabindex="-1"></a> <span class="at">stringsAsFactors =</span> <span class="cn">FALSE</span>))</span>
<span id="cb1-26"><a href="#cb1-26" aria-hidden="true" tabindex="-1"></a><span class="co">#> doc_id text</span></span>
<span id="cb1-27"><a href="#cb1-27" aria-hidden="true" tabindex="-1"></a><span class="co">#> 1 man_comes_around There's a man goin' 'round takin' names</span></span>
<span id="cb1-28"><a href="#cb1-28" aria-hidden="true" tabindex="-1"></a><span class="co">#> 2 wont_back_down Well I won't back down, no I won't back down</span></span>
<span id="cb1-29"><a href="#cb1-29" aria-hidden="true" tabindex="-1"></a><span class="co">#> 3 bird_on_a_wire Like a bird on a wire</span></span></code></pre></div>
<p>All of the tokenizers in this package can accept any of those formats
and will return an identical output for each.</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="fu">library</span>(tokenizers)</span>
<span id="cb2-2"><a href="#cb2-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-3"><a href="#cb2-3" aria-hidden="true" tabindex="-1"></a>tokens_l <span class="ot"><-</span> <span class="fu">tokenize_ngrams</span>(corpus_l, <span class="at">n =</span> <span class="dv">2</span>)</span>
<span id="cb2-4"><a href="#cb2-4" aria-hidden="true" tabindex="-1"></a>tokens_c <span class="ot"><-</span> <span class="fu">tokenize_ngrams</span>(corpus_c, <span class="at">n =</span> <span class="dv">2</span>)</span>
<span id="cb2-5"><a href="#cb2-5" aria-hidden="true" tabindex="-1"></a>tokens_d <span class="ot"><-</span> <span class="fu">tokenize_ngrams</span>(corpus_c, <span class="at">n =</span> <span class="dv">2</span>)</span>
<span id="cb2-6"><a href="#cb2-6" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-7"><a href="#cb2-7" aria-hidden="true" tabindex="-1"></a><span class="co"># Are all these identical?</span></span>
<span id="cb2-8"><a href="#cb2-8" aria-hidden="true" tabindex="-1"></a><span class="fu">all</span>(<span class="fu">identical</span>(tokens_l, tokens_c),</span>
<span id="cb2-9"><a href="#cb2-9" aria-hidden="true" tabindex="-1"></a> <span class="fu">identical</span>(tokens_c, tokens_d),</span>
<span id="cb2-10"><a href="#cb2-10" aria-hidden="true" tabindex="-1"></a> <span class="fu">identical</span>(tokens_l, tokens_d))</span>
<span id="cb2-11"><a href="#cb2-11" aria-hidden="true" tabindex="-1"></a><span class="co">#> [1] TRUE</span></span></code></pre></div>
<p>The output of all of the tokenizers is a named list, where each
element of the list corresponds to a document in the corpus. The names
of the list are the document IDs, and the elements are character vectors
containing the tokens.</p>
<div class="sourceCode" id="cb3"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb3-1"><a href="#cb3-1" aria-hidden="true" tabindex="-1"></a>tokens_l</span>
<span id="cb3-2"><a href="#cb3-2" aria-hidden="true" tabindex="-1"></a><span class="co">#> $man_comes_around</span></span>
<span id="cb3-3"><a href="#cb3-3" aria-hidden="true" tabindex="-1"></a><span class="co">#> [1] "there's a" "a man" "man goin" "goin round" "round takin"</span></span>
<span id="cb3-4"><a href="#cb3-4" aria-hidden="true" tabindex="-1"></a><span class="co">#> [6] "takin names"</span></span>
<span id="cb3-5"><a href="#cb3-5" aria-hidden="true" tabindex="-1"></a><span class="co">#> </span></span>
<span id="cb3-6"><a href="#cb3-6" aria-hidden="true" tabindex="-1"></a><span class="co">#> $wont_back_down</span></span>
<span id="cb3-7"><a href="#cb3-7" aria-hidden="true" tabindex="-1"></a><span class="co">#> [1] "well i" "i won't" "won't back" "back down" "down no" </span></span>
<span id="cb3-8"><a href="#cb3-8" aria-hidden="true" tabindex="-1"></a><span class="co">#> [6] "no i" "i won't" "won't back" "back down" </span></span>
<span id="cb3-9"><a href="#cb3-9" aria-hidden="true" tabindex="-1"></a><span class="co">#> </span></span>
<span id="cb3-10"><a href="#cb3-10" aria-hidden="true" tabindex="-1"></a><span class="co">#> $bird_on_a_wire</span></span>
<span id="cb3-11"><a href="#cb3-11" aria-hidden="true" tabindex="-1"></a><span class="co">#> [1] "like a" "a bird" "bird on" "on a" "a wire"</span></span></code></pre></div>
<p>This format can be coerced to a data frame of document IDs and
tokens, one row per token, using the coercion functions in the tif
package. That tokens data frame would look like this.</p>
<pre><code>#> doc_id token
#> 1 man_comes_around there's a
#> 2 man_comes_around a man
#> 3 man_comes_around man goin
#> 4 man_comes_around goin round
#> 5 man_comes_around round takin
#> 6 man_comes_around takin names
#> 7 wont_back_down well i
#> 8 wont_back_down i won't
#> 9 wont_back_down won't back
#> 10 wont_back_down back down</code></pre>
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