title: Convert a column into multi column by groups
body: <p>I have a data frame(df):</p>
  
  <pre><code>group col
  a     12
  a     15
  a     13
  b     21
  b     23
  </code></pre>
  
  <p>Desired output is also a data frame(df1):</p>
  
  <pre><code>col1  col2
  12    21
  15    23
  13    0
  </code></pre>
  
  <p>Namley, I want to partition "col" of "df" by "group" into multi columns as "col1" and "col2". </p>
  
  <p>When the length of each column is not equal to each other, "0" must be added end of each column untill the length of each column reaches to the maximum column length. </p>