Replace Specific Values In Pandas DataFrame

I have next DataFrame in Pandas: data1 = pd.DataFrame(data=[[1, 10, 100], [2,2,200],[3,3,300], [4,40,400]], columns=['A', 'B', 'C']) Here it is: A B C

Solution 1:

use DataFrame.loc!

mask = data1['A'] == data1['B']
data1.loc[mask, 'C'] = -1

Solution 2:

You can using pandas mask

data1.C=data1.C.mask(data1.A==data1.B,-1)
data1
Out[371]: 
   A   B    C
0  1  10  100
1  2   2   -1
2  3   3   -1
3  4  40  400

Solution 3:

data1.loc[data1.A==data1.B,'C']='-1'

Solution 4:

df['C'] = np.where(df.A == df.B, -1, df.C)