title: concatenate multiple columns based on index in pandas
body: <p>As a follow up to <a href="https://stackoverflow.com/questions/12021730/can-pandas-handle-variable-length-whitespace-as-column-delimeters">this post</a>, I would like to concatenate a number of columns based on their index but I am encountering some problems. In this example I get an Attribute error related to the map function.  Help around this error would be appreciated as would code that does the equivalent concatenation of columns.</p>
  
  <pre><code>    #data
      df = DataFrame({'A':['a','b','c'], 'B':['d','e','f'], 'C':['concat','me','yo'], 'D':['me','too','tambien']})
  
      #row function to concat rows with index greater than 2
      def cnc(row):
          temp = []
          for x in range(2,(len(row))):
              if row[x] != None:
                  temp.append(row[x])
          return map(concat, temp)
  
      #apply function per row
      new = df.apply(cnc,axis=1)
  
      #Expected Output
      new
  
      concat me
      me too
      yo tambien
  </code></pre>
  
  <p>thanks,
  zach cp</p>