How to assign values from column 1 to column 2 when column 1 is > 0 and column 2 is <= 0

Question

I have a df,

delta1    delta2
  0         -1
  2          0
 -1          0
  0          0

I am wondering how to assign values of delta2 to delta1 only if delta1 > 0 and delta2 <= 0; the result look like,

delta1    delta2
  0         -1
  0          0
 -1          0
  0          0 

Answer 1

Using numpy.where:

df['delta1'] = np.where(df.delta1.gt(0) & df.delta2.le(0), df.delta2, df.delta1)

   delta1  delta2
0       0      -1
1       0       0
2      -1       0
3       0       0