title: Return multiple lists in mapply
body: <p>I have a function which I am applying across a list of data frames or matrices (df) using mapply.  The function outputs four different types of data frames (ex. a:d) based on some criteria of transformation of the original data frame, but I am having issues as function will only let me output one.  I have tried to collate them into a list, but when I run a simplified function, I get this.</p>
  
  <pre><code>df1&lt;-matrix(rnorm(10), nrow=10, ncol=10)
  df2&lt;-df1
  df&lt;-list(df1, df2)
  
  func&lt;-function (x) {
    a&lt;-x*1
    b&lt;-x*2
    c&lt;-x*3
    d&lt;-x*4
    return(list(a,b,c,d))
  }
  
  finalresult&lt;-mapply(func, x=df)
  
  str(finalresult)
  
  List of 8
   $ : num [1:10, 1:10] -3.211 -0.121 -0.2 0.491 1.118 ...
   $ : num [1:10, 1:10] -6.422 -0.242 -0.4 0.982 2.235 ...
   $ : num [1:10, 1:10] -9.633 -0.362 -0.6 1.473 3.353 ...
   $ : num [1:10, 1:10] -12.844 -0.483 -0.8 1.964 4.471 ...
   $ : num [1:10, 1:10] -3.211 -0.121 -0.2 0.491 1.118 ...
   $ : num [1:10, 1:10] -6.422 -0.242 -0.4 0.982 2.235 ...
   $ : num [1:10, 1:10] -9.633 -0.362 -0.6 1.473 3.353 ...
   $ : num [1:10, 1:10] -12.844 -0.483 -0.8 1.964 4.471 ...
   - attr(*, "dim")= int [1:2] 4 2
  </code></pre>
  
  <p>In this case you can see it is just giving me the list of the four output data frames (a:d) from df1 and then appends the next set of outputs from df2 right after.  I want to have an output where each data frame transformation is put in a list where I can access it by category (ex. finalresults$a).  Any help would be very much appreciated!</p>
  
  <p>Thanks,
  -Chelsea</p>