title: Create a new column pulls in values where a value equals a column name
body: <p>Apologies if the answer is already out there, I'm new to python and I couldn't find the answer. </p>
  
  <p>That said, I'm playing with a pandas dataframe that has an aggregate sum and various other columns that break down where the sums are coming from. </p>
  
  <p>I would like to come up with a code that creates a new column where the value of one column name's equals the field value of another and if it doesn't equal any column 0, and iterates over every row. </p>
  
  <p>So for instance, I have the following simple table (My dataset is much larger so I would need something to iterate over several rows):</p>
  
  <pre><code>  Value  Aggregate  A  B  C
  0     A          5  4  1  0
  1     B          4  3  1  0
  2     C         12  1  5  6
  3     D          8  4  3  1
  </code></pre>
  
  <p>And would like to get the following:</p>
  
  <pre><code>Value Aggregate A   B   C   New Column
     A    5       4   1   0      4
     B    4       3   1   0      1
     C    12      1   5   6      6
     D    8       4   3   1      0
  </code></pre>