title: Insert Value to a dataframe column
body: <p>I have a pandas dataframe</p>
  <pre><code>0      1      2    3
  0  173.0  147.0  161  162.0
  1    NaN    NaN   23    NaN
  </code></pre>
  <p>I just want to add value a column such as</p>
  <pre><code>           3
         0 161
         1  23
         2 181
  </code></pre>
  <p>But can't go with the approch of <code>loc</code> and <code>iloc</code>. Because the file can contain columns of any length and I will not know <code>loc</code> and <code>iloc</code>. Hence Just want to add value to a column. Thanks in advance.</p>