title: Multiply all values in a pandas df by max value within group
body: <p>I am trying to return the max value within a pandas <code>df</code> for each specific group. I then want to use this max value to multiply separate values and return in a separate column.</p>
  
  <p>For example, using the <code>df</code> below, the max value for each group in <code>Item</code> is:</p>
  
  <pre><code>X = 5
  Y = 2
  </code></pre>
  
  <p>I want to use these values to multiply all other values as a separate column. 
  import pandas as pd</p>
  
  <pre><code>d = ({
      'Item' : ['X','X','X','Y','Y','Y','Y'],                 
      'Count' : [0,2,5,3,1,2,1],                                      
      })
  
  df = pd.DataFrame(data = d)
  </code></pre>
  
  <p>This is my attempt:</p>
  
  <pre><code>df['Mult_max'] = df.groupby('Item').apply(lambda x: x['Count'].max() * x['Count'])
  </code></pre>
  
  <p>Intended Output:</p>
  
  <pre><code>  Group  Value  Mult_max
  0     X      0         0
  1     X      2        10
  2     X      5        25
  3     Y      3         9
  4     Y      1         3
  5     Y      2         6
  6     Y      1         3
  </code></pre>