Multiplying all values in Pandas Dataframe rows

Question

This is basically the dataframe:

      col1    col2    col3    label
row1   1       0       1        1
row2   0       0       0        1
row3   1       1       1        0
row4   1       2       1        0

I basically need it to go over each row, and if label = 0, multiply all the values in the row by -1.

I've tried many different approaches, including:

df.ix[3] = df.ix[3].multiply(-1)

Which returns:

SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame. Try using .loc[row_indexer,col_indexer] = value instead

I've also tried dropping the row and replacing, which doesn't work because the indexes change.

Answer 1

In [156]: df.loc[df.label==0, df.columns.drop('label')] = \
              df.loc[df.label==0, df.columns.drop('label')].mul(-1)

In [157]: df
Out[157]:
      col1  col2  col3  label
row1     1     0     1      1
row2     0     0     0      1
row3    -1    -1    -1      0
row4    -1    -2    -1      0

or bit shorter version:

In [160]: df.loc[df.label==0, df.columns.drop('label')] *= -1

In [161]: df
Out[161]:
      col1  col2  col3  label
row1     1     0     1      1
row2     0     0     0      1
row3    -1    -1    -1      0
row4    -1    -2    -1      0