title: Compute daily climatology using pandas python
body: <p>I am trying to use pandas to compute daily climatology. My code is:</p>
  
  <pre><code>import pandas as pd
  
  dates      = pd.date_range('1950-01-01', '1953-12-31', freq='D')
  rand_data  = [int(1000*random.random()) for i in xrange(len(dates))]
  cum_data   = pd.Series(rand_data, index=dates)
  cum_data.to_csv('test.csv', sep="\t")
  </code></pre>
  
  <p>cum_data is the data frame containing daily dates from 1st Jan 1950 to 31st Dec 1953. I want to create a new vector of length 365 with the first element containing the average of rand_data for January 1st for 1950, 1951, 1952 and 1953. And so on for the second element...</p>
  
  <p>Any suggestions how I can do this using pandas?</p>