根据另一列熊猫数据框的值更改一列的值

Question

I have this pandas dataframe:

id    A    B
 1   nan   0
 2   nan   1
 3   6     0
 4   nan   1
 5   12    1
 6   14    0

I want to change the value of all nan is 'A' based on the value of 'B', for example if B = 0, A should be random number between [0,1] if B = 1, A should be random number between [1,3]

How do i do this?

Answer 1

Solution if performance is important - generate random values by length of DataFrame and then assign values by conditions:

Use numpy.random.randint for generate random values and pass to numpy.select with chainded condition with & for bitwise AND, compare is by Series.isna and Series.eq :

a = np.random.randint(0,2, size=len(df)) #generate 0,1
b = np.random.randint(1,4, size=len(df)) #generate 1,2,3
m1 = df.A.isna()
m2 = df.B.eq(0)
m3 = df.B.eq(1)

df['A'] = np.select([m1 & m2, m1 & m3],[a, b], df.A)
print (df)
   id     A  B
0   1   1.0  0
1   2   3.0  1
2   3   6.0  0
3   4   3.0  1
4   5  12.0  1
5   6  14.0  0