title: Pandas dataframe resample at every nth row
body: <p>I have a script that reads system log files into pandas dataframes and produces charts from those. The charts are fine for small data sets. But when I face larger data sets due to larger timeframe of data gathering, the charts become too crowded to discern.</p>
  
  <p>I am planning to resample the dataframe so that if the dataset passes certain size, I will resample it so there are ultimately only the SIZE_LIMIT number of rows. This means I need to filter the dataframe so every n = actual_size/SIZE_LIMIT rows would aggregated to a single row in the new dataframe. The agregation can be either average value or just the nth row taken as is.</p>
  
  <p>I am not fully versed with pandas, so may have missed some obvious means.  </p>