In pandas, how do I count gender values ​​(or any categorical variable) based on another categorical column?

Question

I have a dataframe as shown below:

gender   doctor name
female       A
 male        B
 male        A
female       C
female       B

How to make calculations based on gender by the name of the doctor?

Answer 1

I think you need groupbywith an aggregate GroupBy.size:

df = df.groupby(['doctor name','gender']).size()
print (df)
doctor name  gender
A            female    1
             male      1
B            female    1
             male      1
C            female    1
dtype: int64

This is the same result as SeriesGroupBy.value_counts, only the values ​​in each group are sorted:

df = df.groupby(['doctor name']).gender.value_counts()
print (df)
doctor name  gender
A            female    1
             male      1
B            female    1
             male      1
C            female    1
Name: gender, dtype: int64

Delay

#[1000000 rows x 2 columns]
np.random.seed(123)
N = 1000000
L1 = ['e', 'f','g','h', 'i', 'j']
L2 = ['female','male']
df = pd.DataFrame({'gender':np.random.choice(L1, N), 
                   'doctor name': np.random.choice(L2, N)})

#print (df)


In [43]: %timeit (df.groupby(['doctor name','gender']).size())
10 loops, best of 3: 141 ms per loop

In [44]: %timeit (df.groupby(['doctor name']).gender.value_counts())
1 loop, best of 3: 254 ms per loop

#output is sorted by index
print (df.groupby(['doctor name','gender']).size())
doctor name  gender
female       e         82944
             f         83422
             g         83706
             h         83200
             i         83004
             j         83521
male         e         83405
             f         83503
             g         82891
             h         83666
             i         83525
             j         83213
dtype: int64

#output is same, only sorted
print (df.groupby(['doctor name']).gender.value_counts())
doctor name  gender
female       g         83706
             j         83521
             f         83422
             h         83200
             i         83004
             e         82944
male         h         83666
             i         83525
             f         83503
             e         83405
             j         83213
             g         82891
Name: gender, dtype: int64

If crosstabthe fastest solution is needed , add unstack:

df1 = df.groupby(['doctor name','gender']).size().unstack(level=0, fill_value=0)
print (df1)
doctor name  A  B  C
gender              
female       1  1  1
male         1  1  0

df2 = df.groupby(['doctor name','gender']).size().unstack(fill_value=0)
print (df2)
gender       female  male
doctor name              
A                 1     1
B                 1     1
C                 1     0

Timings2

#used same df as in timings

In [64]: %timeit (df.groupby(['doctor name','gender']).size().unstack(level=0, fill_value=0))
10 loops, best of 3: 141 ms per loop

In [65]: %timeit (pd.crosstab(df.gender, df['doctor name']))
1 loop, best of 3: 215 ms per loop

In [66]: %timeit (pd.pivot_table(df, index='gender', columns='doctor name', aggfunc=len, fill_value=0))
1 loop, best of 3: 251 ms per loop

Answer 2

Besides groupby, if you are looking for a cross-table wireframe data representation. There are two direct ways to do this.

Using pd.crosstab

In [52]: pd.crosstab(df.gender, df.doctor)
Out[52]:
doctor  A  B  C
gender
female  1  1  1
male    1  1  0

Using pd.pivot_table

In [53]: pd.pivot_table(df, index='gender', columns='doctor', aggfunc=len, fill_value=0)
Out[53]:
doctor  A  B  C
gender
female  1  1  1
male    1  1  0