Unable to make a new column in Pandas dataframe from two existing columns

Question

Here, I'm trying to create a new column 'new' from the sum of two columns using.loc, but I'm unable to create it, it throws an error saying 'W' in invalid key.

This works

df['new'] = df['W'] + df['Y']

This is not working

df = pd.DataFrame([[1.0,5.0,1],[2,np.NaN,2],[np.NaN,np.NaN,3]], columns = ['W','Y','Z'])
df['new'] = df.loc['W'] + df.loc['Y'] 

Answer 1

You need to pass two arguments to loc - row and column. So in your case it will be:

df['new'] = df.loc[:, 'W'] + df.loc[:, 'Y']