Pandas Downsampling Issue

I have a csv file with two columns containing dates and 0 or 1 like so: 17/08/2012 07:47:16 0 17/08/2012 07:54:31 1 17/08/2012 08:02:31 0 17/08/2012 09:22:33 0 17/08/2012 09:58:05

Solution 1:

After a helpful comment from above i realised what was wrong. It is just a matter of labelling. So in reality the date that should return NaN is the 19th but the default setting is label='right' so it was showing as the 20th. When i add label='left' it works fine. Thanks