Add a column based on values present in another column

Question

I have a dataframe as:

id	Value
0	Auto
1	Manual
2	Auto
3	Manual
4	Manual

I want to add another column based on values present in second column as:

id	Value	Flag
0	Auto	Yes
1	Manual
2	auto	Yes
3	manual
4	Manual

I tried below code:

mask = df['Purchase Order Num'].str.contains('Auto', na= False, case=False)
df['Flag'] = np.where(df[mask], 'Yes', '')

I get the error as:

Length of values (2) does not match length of index (5)

What went wrong?

Answer 1

When we doing the np.where we need pass the whole Boolean to it

mask = df['Purchase Order Num'].str.contains('Auto', na= False, case=False)
df['Flag'] = np.where(mask, 'Yes', '')

pandas assign can do

df['Flag'] = ''
df.loc[mask, 'Flag'] = 'Yes'