统计一个值在dataframe（多列）中出现的频率

Question

I want to count the frequency of a value that are same in 2 column, also adding a column at the end that display the counting number & delete the first cloumn.

The dataframe I have

| Column A | Column B | Column C |
| -------- | -------- | -------- |
| Column A | Cat      | Fish     |
| Column A | Cat      | Apple    |
| Column A | Cat      | Apple    |
| Column A | Dog      | Lemon    |
| Column A | Dog      | Fish     |
| Column A | Dog      | Fish     |

The expected outcome is like

| Column A | Column B | Column C | 
| -------- | -------- | -------- | 
| Cat      | Fish     |     1    |
| Cat      | Apple    |     2    |
| Dog      | Lemon    |     1    |
| Dog      | Fish     |     2    |

I have tried the

df['Column B'].value_counts()

But I don't know to handle 2 cloumn at the same time.

Answer 1

You can use GroupBy.count :

out = (
        df.groupby(["Column B", "Column C"],
                   as_index=False, sort=False)
        ["Column A"].count()
       )

# Output:

print(out)
     Column B    Column C  Column A
0   Cat         Fish              1
1   Cat         Apple             2
2   Dog         Lemon             1
3   Dog         Fish              2