[FIXED] Np.where change value in column if another column value is in another dataframe column

Issue

Let me explain the structure of the problem that I'm trying to solve. Let's suppose that we have two dataframes

DF1:

ID	Value
AA	2
AB	1
AC	2
AD	1
AE	2

DF2:

ID	New Value
AA	1
AC	1

If the ID column row in DF1 is in DF2, then I would like to change the value in the same row in DF1 to the one that it has in DF2, so the end result would be something like this:

DF1:

ID	Value
AA	1
AB	1
AC	1
AD	1
AE	2

So far, I have tried attempts with .loc and np.where but none of them where successful, my closest attempt is the following line of code:

DF1['Value'][row] = [DF2['New Value'][row] if ((DF1['ID'][row]).isin(DF2['ID'])) else DF1['Value'][row] for row in DF['ID']]

Solution

here is one way to to do it using map

# set index on ID in DF2 and map to DF
# replace failed mapping with the value in DF
df['Value']=df['ID'].map(df2.set_index(['ID'])['New Value']).fillna(df['Value'])
df

    ID  Value
0   AA  1.0
1   AB  1.0
2   AC  1.0
3   AD  1.0
4   AE  2.0

Answered By - Naveed