Pandas multiply on certain conditions

Question

Current Df of:

XXXX    apples  -1000000    Bob
XXXX    oranges -1000000    Sam
AAAA    apples  -2400000    Bob
XXXX    pears   1000000 Bob
XXXX    pears   1000000 Sam
XXXX    grapes  1000000 Bob
AAAA    grapes  1000000 Bob
XXXX    apples  1200000 Bob
AAAA    apples  1900000 Sam
XXXX    grapes  -1100000    Sam

I want to multiple the qauntity in the 3rd column by -1 if the first column is equal to 'XXXX' nd the fourth column is equal to 'Bob'

I have tried using loc and filtering on the condition but can't seem to get this right

Would be really helpful to provide the sample data as text and not an image. — gbeaven, Jan 14 '20 at 18:34
Please [edit] your question to include your sample data as text, not as code. Please also include a sample of your desired output, and the code for what you've already tried, to make a [mcve] — G. Anderson, Jan 14 '20 at 18:34
Does this answer your question? [Pandas conditional creation of a series/dataframe column](https://stackoverflow.com/questions/19913659/pandas-conditional-creation-of-a-series-dataframe-column) — FBruzzesi, Jan 14 '20 at 18:50

score 2 · Accepted Answer · answered Jan 14 '20 at 18:36

You can use np.where():

df['col_3'] = np.where((df['col_1']=='XXXX') & (df['col_4']=='Bob'), -1*df['col_3'], df['col_3'])

Yields:

  col_1    col_2    col_3 col_4
0  XXXX   apples  1000000   Bob
1  XXXX  oranges -1000000   Sam
2  AAAA   apples -2400000   Bob
3  XXXX    pears -1000000   Bob
4  XXXX    pears  1000000   Sam
5  XXXX   grapes -1000000   Bob
6  AAAA   grapes  1000000   Bob
7  XXXX   apples -1200000   Bob
8  AAAA   apples  1900000   Sam
9  XXXX   grapes -1100000   Sam

score 2 · Answer 2 · edited Mar 31 '20 at 21:12

2

Doing it in-place and maintaining the pandas df syntax -

df['col_3'] = df.where((df['col_1'] == 'XXXX') & (df['col_4'] == 'Bob'))['col_3'] * -1

edited Mar 31 '20 at 21:12

Trenton McKinney

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answered Jan 14 '20 at 18:43

SaRa

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Pandas multiply on certain conditions

2 Answers2