title: Combine .xls files from multiple folders into one data frame
body: <p>I have 96 folders located in the directory ./data*/..
  Some folders contain an .xls file and some do not. 
  I would like to make a data frame where column number 6 from the files is the row names and a count how for each occurence. </p>
  
  <p>Here is a start:</p>
  
  <pre><code>setwd("~/")
  file_list = list.files(pattern="/data*/*.xls")   
  library(data.table)
  lst &lt;- lapply(file_list, function(x) 
    fread(x, select=c("V6"))[, 
                                   list(ID=paste(V1)])
  df &lt;- as.data.frame(Reduce(function(x,y) x[y, on = "ID"], lst))
  </code></pre>