计算数据框每一行中元素的出现

Question

我有一个看起来像这样的数据框

数据框有11列，每列都分配有一个等级。对于每条记录，我需要计算其中的A，B和C的数量。

这是我预期的输出应为

我尝试使用apply函数执行此操作。这是我到目前为止所拥有的

import pandas as pd
# sample data
df_dict = {'level_1': {0: 'C', 1: 'A', 2: 'C', 3: 'B', 4: 'A', 5: 'C', 6: 'A', 7: 'B', 8: 'B'},
           'level_2': {0: 'B', 1: 'B', 2: 'C', 3: 'A', 4: 'A', 5: 'C', 6: 'B', 7: 'C', 8: 'A'},
           'level_3': {0: 'B', 1: 'A', 2: 'B', 3: 'A', 4: 'B', 5: 'B', 6: 'C', 7: 'B', 8: 'C'},
           'level_4': {0: 'A', 1: 'C', 2: 'B', 3: 'C', 4: 'B', 5: 'C', 6: 'A', 7: 'B', 8: 'C'},
           'level_5': {0: 'B', 1: 'B', 2: 'B', 3: 'A', 4: 'A', 5: 'A', 6: 'B', 7: 'B', 8: 'A'},
           'level_6': {0: 'C', 1: 'C', 2: 'C', 3: 'B', 4: 'B', 5: 'B', 6: 'C', 7: 'A', 8: 'C'},
           'level_7': {0: 'C', 1: 'A', 2: 'C', 3: 'C', 4: 'C', 5: 'C', 6: 'C', 7: 'A', 8: 'A'},
           'level_8': {0: 'B', 1: 'A', 2: 'B', 3: 'B', 4: 'B', 5: 'A', 6: 'A', 7: 'A', 8: 'C'},
           'level_9': {0: 'A', 1: 'B', 2: 'A', 3: 'C', 4: 'C', 5: 'B', 6: 'A', 7: 'C', 8: 'B'},
           'level_10': {0: 'B', 1: 'C', 2: 'A', 3: 'A', 4: 'A', 5: 'A', 6: 'A', 7: 'A', 8: 'C'},
           'level_11': {0: 'C', 1: 'B', 2: 'C', 3: 'B', 4: 'C', 5: 'B', 6: 'B', 7: 'C', 8: 'B'}
           }
sample_df = pd.DataFrame(df_dict)

# function to count the values of A, B, C
def count_in_df(series):
    _ = series.value_counts()
    _ = _[['A', 'B', 'C']]
    return _.tolist()

count_df = pd.DataFrame(sample_df.apply(count_in_df, axis=1).tolist(),
                       columns=['counts_of_A', 'counts_of_B', 'counts_of_C'])

# add count information back 
sample_df = sample_df.join(count_df)

这给了我所需的信息，但是问题是代码太慢了。我有大约70万条记录和66列（而不是11列），我需要在这些列上执行此操作，并且花了大约30分钟才能获得结果。

有没有一种方法可以加快代码的速度？我可以尝试的任何优化方法吗？

Answer 1

stack + groupby + value_counts。重命名列，然后追加。

df = (sample_df
      .stack()
      .groupby(level=0)
      .value_counts()
      .unstack(1)
      .add_prefix('counts_of_')
     )

df = pd.concat([sample_df, df], axis=1)

输出：df

   count_of_A  count_of_B  count_of_C
0           2           5           4
1           4           4           3
2           2           4           5
3           4           4           3
4           4           4           3
5           3           4           4
6           5           3           3
7           4           4           3
8           3           3           5

Answer 2

我使用str.get_dummies

sample_df.stack().str.get_dummies().sum(level=0)

Out[142]:
   A  B  C
0  2  5  4
1  4  4  3
2  2  4  5
3  4  4  3
4  4  4  3
5  3  4  4
6  5  3  3
7  4  4  3
8  3  3  5

Answer 3

@ALollz的回答很好。但是我的方法是这样的。

>>> dummy_df = pd.get_dummies(sample_df)
>>> sample_df['count_of_A'] = dummy_df.filter(regex='level_(\d+)_A').sum(axis=1)
>>> sample_df['count_of_A']
0    2
1    4
2    2
3    4
4    4
5    3
6    5
7    4
8    3

类似地，如果您有多个grades。

>>> grades = list('ABC')
>>> for grade in grades:
...     sample_df[f'count_of_{grade}'] = dummy_df.filter(regex=f'level_(\d+)_{grade}').sum(axis=1)
... 
>>> sample_df.filter(regex='count_of_')
   count_of_A  count_of_B  count_of_C
0           2           5           4
1           4           4           3
2           2           4           5
3           4           4           3
4           4           4           3
5           3           4           4
6           5           3           3
7           4           4           3
8           3           3           5