Remove rows that two columns have the same values by pandas

Question

Input：

    S   T   W      U
0   A   A   1   Undirected
1   A   B   0   Undirected
2   A   C   1   Undirected
3   B   A   0   Undirected
4   B   B   1   Undirected
5   B   C   1   Undirected
6   C   A   1   Undirected
7   C   B   1   Undirected
8   C   C   1   Undirected

Output：

    S   T   W      U
1   A   B   0   Undirected
2   A   C   1   Undirected
3   B   A   0   Undirected
5   B   C   1   Undirected
6   C   A   1   Undirected
7   C   B   1   Undirected

For column S and T ,rows(0,4,8) have same values. I want to drop these rows.

Trying:

I used df.drop_duplicates(['S','T'] but failed, how could I get the results.

Answer 1

You need boolean indexing:

print (df['S'] != df['T'])
0    False
1     True
2     True
3     True
4    False
5     True
6     True
7     True
8    False
dtype: bool

df = df[df['S'] != df['T']]
print (df)
   S  T  W           U
1  A  B  0  Undirected
2  A  C  1  Undirected
3  B  A  0  Undirected
5  B  C  1  Undirected
6  C  A  1  Undirected
7  C  B  1  Undirected

Or query:

df = df.query("S != T")
print (df)
   S  T  W           U
1  A  B  0  Undirected
2  A  C  1  Undirected
3  B  A  0  Undirected
5  B  C  1  Undirected
6  C  A  1  Undirected
7  C  B  1  Undirected