title: Subset data based on partial match of column names
body: <p>I need to subset a df to include certain strings. Some of these are full column names, and the following works fine:</p>
  
  <pre><code>testData[,c("FullColName1","FullColName2","FullColName3")]
  </code></pre>
  
  <p>My problem is that I need to expand this to also include column names that contain specific strings that may partially match to some other column names. These strings include letters and symbols:</p>
  
  <pre><code>"PartString1()","PartString2()"
  </code></pre>
  
  <p>I tried putting wildcards around these. (I've indicated this below with the prefix "star" because the "*" symbol didn't render correctly.)</p>
  
  <pre><code>testData[ ,c("FullColName1","FullColName2","FullColName3",
               "starPartString1()star","starPartString2()star")]
  </code></pre>
  
  <p>But I'm getting an error message: undefined columns selected. I can't figure out if or how I need grep to make this work.</p>