Plot number of occurrences from Pandas DataFrame

Question

I have a DataFrame with two columns. One of them is containing timestamps and another one - id of some action. Something like that:

2000-12-29 00:10:00     action1
2000-12-29 00:20:00     action2
2000-12-29 00:30:00     action2
2000-12-29 00:40:00     action1
2000-12-29 00:50:00     action1
...
2000-12-31 00:10:00     action1
2000-12-31 00:20:00     action2
2000-12-31 00:30:00     action2

I would like to know how many actions of certain type have been performed in a certain day. I.e. for every day, I need to count the number of occurrences of actionX and plot this data with date on X axis and number of occurrences of actionX on Y axes, for each date.

Of course I can count actions for each day naively just by iterating through my dataset. But what's the "right way" to do in with pandas/matplotlib?

Answer 1

You can get the counts by using

df.groupby([df.index.date, 'action']).count()

or you can plot directly using this method

df.groupby([df.index.date, 'action']).count().plot(kind='bar')

You could also just store the results to count and then plot it separately. This is assuming that your index is already in datetimeindex format, otherwise follow the directions of @mkln above.