How to speed up pandas row filtering by string matching?

Question

I often need to filter pandas dataframe df by df[df[\'col_name\']==\'string_value\'], and I want to speed up the row selction operation, is there a qui

Answer 1

Depending on what you want to do with the selection afterwards, and if you have to make multiple selections of this kind, the groupby functionality can also make things faster (at least with the example).

Even if you only have to select the rows for one string_value, it is a little bit faster (but not much):

In [11]: %timeit df[df['STK_ID']=='A0003']
1 loops, best of 3: 626 ms per loop

In [12]: %timeit df.groupby("STK_ID").get_group("A0003")
1 loops, best of 3: 459 ms per loop

But subsequent calls to the GroupBy object will be very fast (eg to select the rows of other sting_values):

In [25]: grouped = df.groupby("STK_ID")

In [26]: %timeit grouped.get_group("A0003")
1 loops, best of 3: 333 us per loop