Groupby value counts on the dataframe pandas

问题

I have the following dataframe:

df = pd.DataFrame([
    (1, 1, \'term1\'),
    (1, 2, \'term2\'),
    (1, 1, \'term1\'),
    (1, 1, \'term2\'),
    (2, 2, \'term3\'),
    (2, 3, \'term1\'),
    (2, 2, \'term1\')
], columns=[\'id\', \'group\', \'term\'])

I want to group it by id and group and calculate the number of each term for this id, group pair.

So in the end I am going to get something like this:

I was able to achieve what I want by looping over all the rows with df.iterrows() and creating a new dataframe, but this is clearly inefficient. (If it helps, I know the list of all terms beforehand and there are ~10 of them).

It looks like I have to group by and then count values, so I tried that with df.groupby([\'id\', \'group\']).value_counts() which does not work because value_counts operates on the groupby series and not a dataframe.

Anyway I can achieve this without looping?

回答1:

I use groupby and size

df.groupby(['id', 'group', 'term']).size().unstack(fill_value=0)

---

Timing

1,000,000 rows

df = pd.DataFrame(dict(id=np.random.choice(100, 1000000),
                       group=np.random.choice(20, 1000000),
                       term=np.random.choice(10, 1000000)))

回答2:

using pivot_table() method:

In [22]: df.pivot_table(index=['id','group'], columns='term', aggfunc='size', fill_value=0)
Out[22]:
term      term1  term2  term3
id group
1  1          2      1      0
   2          0      1      0
2  2          1      0      1
   3          1      0      0

Timing against 700K rows DF:

In [24]: df = pd.concat([df] * 10**5, ignore_index=True)

In [25]: df.shape
Out[25]: (700000, 3)

In [3]: %timeit df.groupby(['id', 'group', 'term'])['term'].size().unstack(fill_value=0)
1 loop, best of 3: 226 ms per loop

In [4]: %timeit df.pivot_table(index=['id','group'], columns='term', aggfunc='size', fill_value=0)
1 loop, best of 3: 236 ms per loop

In [5]: %timeit pd.crosstab([df.id, df.group], df.term)
1 loop, best of 3: 355 ms per loop

In [6]: %timeit df.groupby(['id','group','term'])['term'].size().unstack().fillna(0).astype(int)
1 loop, best of 3: 232 ms per loop

In [7]: %timeit df.groupby(['id', 'group', 'term']).size().unstack(fill_value=0)
1 loop, best of 3: 231 ms per loop

Timing against 7M rows DF:

In [9]: df = pd.concat([df] * 10, ignore_index=True)

In [10]: df.shape
Out[10]: (7000000, 3)

In [11]: %timeit df.groupby(['id', 'group', 'term'])['term'].size().unstack(fill_value=0)
1 loop, best of 3: 2.27 s per loop

In [12]: %timeit df.pivot_table(index=['id','group'], columns='term', aggfunc='size', fill_value=0)
1 loop, best of 3: 2.3 s per loop

In [13]: %timeit pd.crosstab([df.id, df.group], df.term)
1 loop, best of 3: 3.37 s per loop

In [14]: %timeit df.groupby(['id','group','term'])['term'].size().unstack().fillna(0).astype(int)
1 loop, best of 3: 2.28 s per loop

In [15]: %timeit df.groupby(['id', 'group', 'term']).size().unstack(fill_value=0)
1 loop, best of 3: 1.89 s per loop

回答3:

Instead of remembering lengthy solutions, how about the one that pandas has built in for you:

df.groupby(['id', 'group', 'term']).count()

回答4:

You can use crosstab:

print (pd.crosstab([df.id, df.group], df.term))
term      term1  term2  term3
id group                     
1  1          2      1      0
   2          0      1      0
2  2          1      0      1
   3          1      0      0

Another solution with groupby with aggregating size, reshaping by unstack:

df.groupby(['id', 'group', 'term'])['term'].size().unstack(fill_value=0)

term      term1  term2  term3
id group                     
1  1          2      1      0
   2          0      1      0
2  2          1      0      1
   3          1      0      0

Timings:

df = pd.concat([df]*10000).reset_index(drop=True)

In [48]: %timeit (df.groupby(['id', 'group', 'term']).size().unstack(fill_value=0))
100 loops, best of 3: 12.4 ms per loop

In [49]: %timeit (df.groupby(['id', 'group', 'term'])['term'].size().unstack(fill_value=0))
100 loops, best of 3: 12.2 ms per loop

来源：https://stackoverflow.com/questions/39132742/groupby-value-counts-on-the-dataframe-pandas