Pandas conditional comparison: based on multiple columns

问题

I have a df

   col1  col2  col3  col4  
0     1     2     3     4    
1     2     2     3     4    
2     3     4     3     5   
3     4     3     2     1   

And I want to add a new column based on:

if (col1 & col2) < (col3 & col4) --- > 2

I followed the approach similar to this post, just without max() as follow but all didn't work:

df[['col1','col2']] < df[['col3','col4']] 

(df['col1'] and df['col2']) < (df['col3'] and df['col4'])

What's the correct way to do it? Thanks.

回答1:

mask = df[['col1','col2']].max(1) < df[['col3','col4']].min(1)

df['new_col'] = np.where(mask, 2, np.nan)

Output:

   col1  col2  col3  col4  new_col
0     1     2     3     4      2.0
1     2     2     3     4      2.0
2     3     4     3     5      NaN
3     4     3     2     1      NaN

来源：https://stackoverflow.com/questions/62603518/pandas-conditional-comparison-based-on-multiple-columns