python - pandas dataframe remove constant column

Question

I have a dataframe that may or may not have columns that are the same value. For example

    row    A    B
    1      9    0
    2      7    0
    3      5    0
    4      2    0

I'd like to return just

   row    A  
   1      9    
   2      7    
   3      5    
   4      2

Is there a simple way to identify if any of these columns exist and then remove them?

Answer 1

I believe this option will be faster than the other answers here as it will traverse the data frame only once for the comparison and short-circuit if a non-unique value is found.

>>> df

   0  1  2
0  1  9  0
1  2  7  0
2  3  7  0

>>> df.loc[:, (df != df.iloc[0]).any()] 

   0  1
0  1  9
1  2  7
2  3  7