title: Resampling data by week
body: <p>I have a time series dataset of 100 users looking at 365 days of transactions. The dataframe is currently set up like the following:</p>
  
  <pre><code>      date    2018-04-01 2018-04-02 2018-04-03 2018-04-04  2018-04-05 ...
  userid
     1              0          0             0        0          13.40
     2            12.32        0             0        0           3.60
     3            11.32        0           14.22      0            0
     4              0          0             0        0           9.87
     5              0          0           19.52      0            0
    ...
  </code></pre>
  
  <p>I want to resample this to 52 weeks, taking the sums of the transactions every 7 days. How would I do this?</p>