title: Merging/combining specific columns from separate data frames or objects within a list
body: <p>I have been searching in vain to find a solution to efficiently combine specific columns from separate data frames or from separate objects within the same list into new data frames.  I have 5 data frames that all have the same row names (e.g. x, y, z) and the same column names (V1, V2, V3,...V1000).</p>
  
  <pre><code>   V1   V2   V3   V4...      V1    V2   V3   V4...
  x   1    5    8    9      x   2     7    9    5
  y   2    7    4    8      y   4     6    5    6
  z   4    4    5    9      z   3     4    8    7
  </code></pre>
  
  <p>What I need to do is to extract V1 from all five frames and make a new data frame with those five V1 columns, and then do the same for the remaining V2-V1000 to get something like:</p>
  
  <pre><code>   V1   V1   V1   V1   V1         V2    V2   V2   V2   V2
  x   1    5    8    9    5      x   2     7    9    5    5
  y   2    7    4    8    8      y   4     6    5    6    4
  z   4    4    5    9    7      z   3     4    8    7    7
  </code></pre>
  
  <p>Eventually, I need to apply another function to all 1000 of the newly created data frames so if there is a way to loop this merging process and place the 1000 new frames into a new set of frames, that would be ideal.</p>
  
  <p>I have tried various forms of merge, cbind, sapply and other solutions I have found suggested here and elsewhere on the web.  The best I've been able to come up with is getting all five data frames into a single list and then using sapply to merge V1 from each object using <strong>sapply(y, "[[",2)</strong> where y is the list and 2 corresponds to the V1 column in each object.  However, I can't seem to get this looped.  I could use this code to manually create the 1000 new data frames but that would take forever.</p>
  
  <p>Any suggestions or directions to other answers that might work would be appreciated! </p>