python - 如何用python计算一列中每一行的唯一值？

Question

我有这样一个数据框:

id countries
01 [UK,UK,UK,US]
02 [US,US,US,US]
03 [FR,UK,CN,US]

我想计算每个 ID 存在多少个国家/地区。结果应该是这样的:

id countries counts
01 [UK,UK,UK,US] 2
02 [US,US,US,US] 1
03 [FR,UK,CN,US] 4

Answer 1

如果值是list，则将它们转换为set并获取length:

print (type(df.loc[0, 'countries']))
<class 'list'>

df['counts'] = df['countries'].apply(lambda x: len(set(x)))
print (df)
   id         countries  counts
0   1  [UK, UK, UK, US]       2
1   2  [US, US, US, US]       1
2   3  [FR, UK, CN, US]       4

或者如果值为字符串，首先删除[]并拆分:

print (type(df.loc[0, 'countries']))
<class 'str'>

df['counts'] = df['countries'].str.strip('[]').str.split(',').apply(lambda x: len(set(x)))
print (df)
   id      countries  counts
0   1  [UK,UK,UK,US]       2
1   2  [US,US,US,US]       1
2   3  [FR,UK,CN,US]       4