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copied!<p>The answer already given using <code>stringr</code> is excellent. That package provides you with some very helpful string munging tools. </p> <p>If you want to only use base, you could do this with <code>gsub</code>. Assuming your punctuation stays the same and there will not be any embedded periods or underscores in the X, Y or Z something like this should work</p> <pre><code>f <- 'X_Y.doc.Z.x_y_z' gsub('^.+_(.+)\\.doc\\.(.+)\\..+_.+$', '\\1 \\2', f) </code></pre> <p>which returns:</p> <pre><code>"Y Z" </code></pre> <p>you could put whatever you want in there though to make it easier to get at each piece or could do this in two lines returning one each. And remember, R almost never changes data in place. You need to assign the output of a function to a variable like below. Otherwise it will just print to the console and be "lost" (this is true <em>most</em> of the time).</p> <pre><code>y <- gsub('^.+_(.+)\\.doc\\..+\\..+_.+$', '\\1', f) z <- gsub('^.+_.+\\.doc\\.(.+)\\..+_.+$', '\\1', f) </code></pre> <p>Lets break it down.</p> <p><code>^</code> specifies the beginning of a line. its good to be explicit. similarly <code>$</code> identifies the end of a line.</p> <p><code>.</code> represents any character and following it with a <code>+</code> means one or more of any character. If you used <code>.*</code> instead of <code>.+</code> it would mean zero or more of any character and that isnt what we want. If i want to write a normal <code>.</code> I need to escape it since its a special character. <code>\</code> is the escape character both for regular expressions and for R. So... you need two. To write a normal period you need to write <code>\\.</code></p> <p>Clear to be sure. Finally the parentheses represent a group I want to save. They can be referenced later using numbers indicating the order you saved them. In some languages these parentheses need to be escaped also, but not R.</p>

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