Find symmetric pairs quickly in numpy

Question

from itertools import product
import pandas as pd

df = pd.DataFrame.from_records(product(range(10), range(10)))
df = df.sample(90)
df.columns = \"c1 c2\".split()
df         


        

Answer 1

I will do

df[~pd.DataFrame(np.sort(df.values,1)).duplicated().values]

From pandas and numpy tri

s=pd.crosstab(df.c1,df.c2)
s=s.mask(np.triu(np.ones(s.shape)).astype(np.bool) & s==0).stack().reset_index()