title: Pandas dataframe, grouping 3 columns and counting the third
body: <p>I'm trying to group a dataframe by 3 columns, date, time and article, and return an object where i have the groups of date, time and article, and the count of each article per time (hour).</p>
  
  <p>This code does the trick with the grouping, but I can't figure out how to also get the count:</p>
  
  <pre><code>dfs.groupby([dfs['Dato'].dt.date,dfs['Tid'].dt.hour,dfs['Varenavn']])
  </code></pre>
  
  <p>so this could be my input:</p>
  
  <pre><code>01.01.2018   0901  Car
  01.01.2018   0905  Car
  01.01.2018   0945  Horse
  01.01.2018   1005  Car
  02.01.2018   0900  Horse
  02.01.2018   0915  Horse
  02.01.2018   1050  Car
  02.01.2018   1055  Horse
  </code></pre>
  
  <p>Wanted output:</p>
  
  <pre><code>01.01.2018 09-10 Car   2
                   Horse 1
  01.01.2018 10-11 Car   1
  02.01.2018 09-10 Horse 2 
  02.01.2018 10-11 Car   1 
                   Horse 1
  </code></pre>
  
  <p>My overall goal is to find how many items were sold per hour per day, from a dataframe containing every sold item, at what time and at what date</p>