Python 两个柱的滚动发生

在pandas中，我有两个系列的x行，我想添加一列，其中我得到col1中的值从第一行到x-1行出现的滚动次数

df如下所示：

   col1 col2
0  B    A
1  B    C
2  A    B
3  A    B
4  A    C
5  B    A

所需输出为

   col1 col2 freq
0  B    A    0
1  B    C    1
2  A    B    1
3  A    B    2
4  A    C    3    #A appears 3 times in the two columns from row 0 to 3
5  B    A    4    #B appears 4 times in the two columns from row 0 to 4

来自初学者的提前感谢， G

印刷品：

  col1 col2  freq
0    B    A     0
1    B    C     1
2    A    B     1
3    A    B     2
4    A    C     3
5    B    A     4

编辑（任意列数的解决方案）：

---

无论df中有多少列，这都将解决此问题

import pandas as pd
import numpy as np

def add(d1,d2):
    # adding two dictionary
    for i in d2.keys():
        if i in d1.keys():
            d1[i] = d1[i] +d2[i]
        else:
            d1[i] = d2[i]
    return d1

if __name__ == '__main__':
    counts = {}
    df = pd.DataFrame({"a":[1, 2, 3, 1, 2], "b":[2, 1, 2, 3, 1]})
    col = list(df)
    for ind, it in df.iterrows():
        unique,count = np.unique(it,return_counts=True)
        unique_dict = dict(zip(unique, count))
        counts = add(counts,unique_dict)

        df.loc[ind, "freq"] = counts[it[col[0]]]
    df["freq"] =df["freq"]-1

---

让我们使用一些数据帧重塑、groupby和cumcount：

dfs = df.stack()
df['freq'] = dfs.groupby(dfs).cumcount().unstack()['col1']
print(df)

输出：

  col1 col2  freq
0    B    A     0
1    B    C     1
2    A    B     1
3    A    B     2
4    A    C     3
5    B    A     4

---

如果我有更多的感冒会怎么样

dfs = df.stack()
df['freq'] = dfs.groupby(dfs).cumcount().unstack()['col1']
print(df)

  col1 col2  freq
0    B    A     0
1    B    C     1
2    A    B     1
3    A    B     2
4    A    C     3
5    B    A     4