title: How to fill a dataframe at specific index and column by iterating over rows of another dataframe?
body: <p>I have a dataframe named <code>user_follow</code> that looks like this..</p>
  <pre><code>followerId  followingId
  
  abc1998     abc1997
  abc1998     abc1991
  abc1998     abc1992
  abc1998     abc1994
  abc1998     abc1995
  abc1998     abc1996
  abc1998     abc2035
  </code></pre>
  <p>The 'followerId' and 'followingId' are ID of various users. I have another list <code>uniqueUsers</code> that has a list o almost 100 total users.</p>
  <p>I have created a dataframe <code>df</code> with all 0 values and indices and rows as elements of <code>uniqueUsers</code>.</p>
  <pre><code>          abc2003 abc2022 abc2023 ... abc1997 abc1998 abc2035 abc1996   
  abc2003     0       0       0     ...   0       0       0        0
  abc2022     0       0       0     ...   0       0       0        0
  abc2023     0       0       0     ...   0       0       0        0
  abc2024     0       0       0     ...   0       0       0        0
  abc2027     0       0       0     ...   0       0       0        0
  .
  .
  .
  </code></pre>
  <p>So, the above dataframe has 100 rows and 100 columns.</p>
  <p>I want to fill the above dataframe <code>df</code> by iterating through the dataframe <code>user_follow</code>. For every (followerId, followingId) from <code>user_follow</code>, I want to fill '1' in the corresponding (row,column) of the above dataframe <code>df</code>.  Here, row/index and columns are the unique users from <code>uniqueUsers</code> list.</p>
  <p>Any help on this?</p>