title: Concatenate all columns in a pandas dataframe
body: <p>I have multiple pandas dataframe which may have different number of columns and the number of these columns typically vary from 50 to 100. I need to create a final column that is simply all the columns concatenated. Basically the string in the first row of the column should be the sum(concatenation) of the strings on the first row of all the columns. I wrote the loop below but I feel there might be a better more efficient way to do this. Any ideas on how to do this</p>
  
  <pre><code>num_columns = df.columns.shape[0]
  col_names = df.columns.values.tolist()
  df.loc[:, 'merged'] = ""
  for each_col_ind in range(num_columns):
      print('Concatenating', col_names[each_col_ind])
      df.loc[:, 'merged'] = df.loc[:, 'merged'] + df[col_names[each_col_ind]]
  </code></pre>