Python dataframe:: get count across two columns for each unique value in either column

Question

I have a python dataframe with columns, 'Expected' vs 'Actual' that shows a product (A,B,C or D) for each record

ID	Expected	Actual
1	A	B
2	A	A
3	C	B
4	B	D
5	C	D
6	A	A
7	B	B
8	A	D

I want to get a count from both columns for each unique value found in both columns (both columns dont share all the same products). So the result should look like this,

Value	Expected	Actual
A	4	2
B	2	3
C	2	0
D	0	3

Thank you for all your help

Answer 1

I would do it following way

import pandas as pd
df = pd.DataFrame({'Expected':['A','A','C','B','C','A','B','A'],'Actual':['B','A','B','D','D','A','B','D']})
ecnt = df['Expected'].value_counts()
acnt = df['Actual'].value_counts()
known = sorted(set(df['Expected']).union(df['Actual']))
cntdf = pd.DataFrame({'Value':known,'Expected':[ecnt.get(k,0) for k in known],'Actual':[acnt.get(k,0) for k in known]})
print(cntdf)

output

  Value  Expected  Actual
0     A         4       2
1     B         2       3
2     C         2       0
3     D         0       3

Explanation: main idea here is having separate value counts for Expected column and Actual column. If you wish to rather have Value as Index of your pandas.DataFrame you can do

...
cntdf = pd.DataFrame([acnt,ecnt]).T.fillna(0)
print(cntdf)

output

   Actual  Expected
D     3.0       0.0
B     3.0       2.0
A     2.0       4.0
C     0.0       2.0

Answer 2

You can use apply and value_counts

df = pd.DataFrame({'Expected':['A','A','C','B','C','A','B','A'],'Actual':['B','A','B','D','D','A','B','D']})
df.apply(pd.Series.value_counts).fillna(0)

output:

   Expected     Actual
A   4.0         2.0
B   2.0         3.0
C   2.0         0.0
D   0.0         3.0