How to count the unique values of each row in one column with python?

Question

I have such a data frame:

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

I want to count how many countries exist for each id. Like the result should be like:

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

Answer 1

If values are list s convert them to set and get 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

Or if values are strings first remove [] and split:

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