title: What are methods to distribute volumes over a calendar in pandas
body: <p>Currently I am conceptually stuck on how to proceed with the issue below. I am basically having a list with Sold Items per country and item type.</p>
  
  <p>My output should be a calendar with the returned items per item type and country. </p>
  
  <p>The first dataframe that specifies the <code>order_date</code>, <code>Type</code>, <code>Country</code> and <code>Volume</code>.</p>
  
  <pre><code>import pandas as pd
  d = {'order_date': ['01.02.2020', '01.02.2020'], 'Type': ['Book', 'CD'], 'Country':['IT','AT'], 'Volume':[300,4000]}
  df = pd.DataFrame(data=d)
  df
  </code></pre>
  
  <p>This is basically just a list of Sold Items per day per country and item type.</p>
  
  <pre><code>Index  order_date   Type    Country   Volume
  0      01.02.2020   Book    IT        300
  1      01.02.2020   CD      AT        4000
  </code></pre>
  
  <p>My second dataframe would be: </p>
  
  <pre><code>d2 = {'return-t[d]': [0,0,0,0,1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4], 'Type': ['Book', 'CD','Book', 'CD','Book', 'CD','Book', 'CD','Book', 'CD','Book', 'CD','Book', 'CD','Book', 'CD','Book', 'CD','Book', 'CD'], 'Country':['IT','AT','IT','AT','IT','AT','IT','AT','IT','AT','IT','AT','IT','AT','IT','AT','IT','AT','IT','AT'], 'distr-percentage':[0.01,0.01,0.01,0.01,0.01,0.01,0.01,0.01, 0.01,0.01,0.01,0.01, 0.01,0.01,0.01,0.01, 0.01,0.01,0.01,0.01]}
  df2 = pd.DataFrame(data=d2,index=None)
  df2
  </code></pre>
  
  <p>This is based on my analysis of returned items. <code>order_date</code> + <code>return-t[d]</code> is the return date. For example the share of sold books in italy that gets returned on <code>order_date</code>+ 0 days is 0.01. </p>
  
  <pre><code>   return-t[d]  Type    Country  distr-percentage
  0   0           Book    IT       0.01
  1   0           CD      AT       0.01
  2   0           Book    IT       0.01
  3   0           CD      AT       0.01
  4   1           Book    IT       0.01
  5   1           CD      AT       0.01
  6   1           Book    IT       0.01
  7   1           CD      AT       0.01
  </code></pre>
  
  <p>My problem now is that I am stuck on how to proceed. I want to create a simple calendar that gives information how many returned items on that date.
  The only thing I could think of was creating another calendar in the columns and distribute the volumes there and in the end group by the date columns. But seemed like overkill.</p>