df1
df2
df2[['Item1', 'Item2']] = df2[['Item2', 'Item1']]
df2['Moves'] = df2['Moves'] * -1
df2
df3 = df1.append(df2)
df3.groupby(['Item1', 'Item2'], as_index=False).sum()
Calculate pairwise difference from specific columns in a dataframe