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POReturn original search terms for grep in R
 

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  1. POReturn original search terms for grep in R
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    <p>I have a list of items and a list of search terms, and I am trying to do two things:</p> <ol> <li>Search through the items for matches to any of the search terms, and return true iff a match is found.</li> <li>For all items where true is returned (i.e., there was a match), I would like to also return the original search term which was matched in step 1.</li> </ol> <p>So, given the following data frame:</p> <pre><code> items 1 alex 2 alex is a person 3 this is a test 4 false 5 this is cathy </code></pre> <p>and the following list of search terms:</p> <pre><code>"alex" "bob" "cathy" "derrick" "erica" "ferdinand" </code></pre> <p>I would like to create the following output:</p> <pre><code> items matches original 1 alex TRUE alex 2 alex is a person TRUE alex 3 this is a test FALSE &lt;NA&gt; 4 false FALSE &lt;NA&gt; 5 this is cathy TRUE cathy </code></pre> <p>Step 1 is fairly straightforward, but I am having trouble with step (2). To create the 'matches' column, I use <code>grepl()</code> to create a variable which is <code>TRUE</code> if a row in <code>d$items</code> is in the list of search terms, and <code>FALSE</code> otherwise. </p> <p>For step 2, my thought was that I should be able to just use <code>grep()</code> while specifying <code>value = T</code>, as shown in my code below. However, this returns the wrong value: rather than return the original search term which was matched by grep, it returns the value of the item that was matched. So I get the following output:</p> <pre><code> items matches original 1 alex TRUE alex 2 alex is a person TRUE alex is a person 3 this is a test FALSE &lt;NA&gt; 4 false FALSE &lt;NA&gt; 5 this is cathy TRUE this is cathy </code></pre> <p>This is the code I am using right now. Any thoughts would be much appreciated!</p> <pre><code># Dummy data and search terms d = data.frame(items = c("alex", "alex is a person", "this is a test", "false", "this is cathy")) searchTerms = c("alex", "bob", "cathy", "derrick", "erica", "ferdinand") # Return true iff search term is found in items column, not between letters d$matches = grepl(paste("(^| |[^abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVQXYZ])", searchTerms, "($| |[^abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVQXYZ])", sep = "", collapse = "|"), d[,1], ignore.case = TRUE ) # Subset data dMatched = d[d$matches==T,] # This is where the problem is: return the value that was originally matched with grepl above dMatched$original = grep(paste("(^| |[^abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVQXYZ])", searchTerms, "($| |[^abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVQXYZ])", sep = "", collapse = "|"), dMatched[,1], ignore.case = TRUE, value = TRUE ) d$original[d$matches==T] = dMatched$original </code></pre>
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    1. USSteve
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    1. COYou can replace the long strings of letters with `[:alpha:]`.
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    2. COYou might want to check out the `regmatches` function.
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    3. CO@Thomas: Thanks for the tip. [:alpha:] and other predefined character classes never seem to work for me, though. It must have something to do with my locale. From the regular expression documentation on character classes: "(Because their interpretation is locale- and implementation-dependent, they are best avoided.) The only portable way to specify all ASCII letters is to list them all as the character class [ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz]."
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