CODEWITHSUNDEEP
pythonpandasdataframeconditional-statements
codemunchkin
codemunchkin

Reputation: 47

Filling a Column in a Dataframe conditionally using values from another Dataframe

I have 2 dataframes one is the lookup dataframe called 'database' and another dataframe called 'df' for which the values are to be filled conditionally with the values from the 'database' dataframe column called 'Value'

I tried merge and it works but it doesn't conditionally fill in values, I want to fill in the values for every row with '1' in the 'Variab' column of df, 'col2' is just an empty column so ignore that.

Thanks in advance!

Before: df

ID Variab col2
A2 1
A2 1
A3 0
A3 1
A4 1
A3 0
A3 1
A4 1
A3 0
A3 1
A4 1

Before: database

ID Value
A2 Ball
A3 Sky
A4 Bird
A5 Fly
A6 Pizza

After: (the objective)

ID Variab Value col 2
A2 1 Ball
A2 1 Ball
A3 0
A3 1 Sky
A4 1 Bird
A3 0
A3 1 Sky
A4 1 Bird
A3 0
A3 1 Sky
A4 1 Bird

Upvotes: 0

Views: 330

Answers (1)

Corralien
Corralien

Reputation: 120399

Use mask before merge:

df['Value'] = df.mask(df['Variab'].eq(0)).merge(db, on='ID', how='left')['Value']
print(df)

# Output
    ID  Variab  col2 Value
0   A2     1.0   NaN  Ball
1   A2     1.0   NaN  Ball
2   A3     0.0   NaN   NaN
3   A3     1.0   NaN   Sky
4   A4     1.0   NaN  Bird
5   A3     0.0   NaN   NaN
6   A3     1.0   NaN   Sky
7   A4     1.0   NaN  Bird
8   A3     0.0   NaN   NaN
9   A3     1.0   NaN   Sky
10  A4     1.0   NaN  Bird

Upvotes: 3

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