### Question :

Comparing 2 columns of two Python Pandas dataframes and getting the common rows

I have 2 Dataframe as follows:

```
DF1=
A B C D
0 AA BA KK 0
1 AD BD LL 0
2 AF BF MM 0
DF2=
K L
0 AA BA
1 AD BF
2 AF BF
```

At the end what I want to get is:

```
DF1=
A B C D
0 AA BA KK 1
1 AD BD LL 0
2 AF BF MM 1
```

So, I want to compare two dataframe, I want to see which rows of first data frame (for column A and B) are in common of of second dataframe(Column K and L) and assign 1 on the coulmn D of first dataframe.

I can use for loop, but It will be very slow for large number of entries.

Any clue or suggestion will be appreciated.

##
Answer #1:

This would be easier if you renamed the columns of `df2`

and then you can compare row-wise:

```
In [35]:
df2.columns = ['A', 'B']
df2
Out[35]:
A B
0 AA BA
1 AD BF
2 AF BF
In [38]:
df1['D'] = (df1[['A', 'B']] == df2).all(axis=1).astype(int)
df1
Out[38]:
A B C D
0 AA BA KK 1
1 AD BD LL 0
2 AF BF MM 1
```

##
Answer #2:

```
df1['ColumnName'].isin(df2['ColumnName']).value_counts()
```

##
Answer #3:

This is how I solved it:

```
df1 = pd.DataFrame({"A":['AA','AD','AD'], "B":['BA','BD','BF']})
df2 = pd.DataFrame({"A":['AA','AD'], 'B':['BA','BF']})
df1['compressed']=df1.apply(lambda x:'%s%s' % (x['A'],x['B']),axis=1)
df2['compressed']=df2.apply(lambda x:'%s%s' % (x['A'],x['B']),axis=1)
df1['Success'] = df1['compressed'].isin(df2['compressed']).astype(int)
print df1
A B compressed Success
0 AA BA AABA 1
1 AD BD ADBD 0
2 AD BF ADBF 1
```

##
Answer #4:

`DF1.merge(right=DF2,left_on=[DF1.A,DF1.B],right_on=[DF2.K,DF2.L], indicator=True, how='left')`

gives:

`A B C D K L _merge`

0 AA BA KK 0 AA BA both

1 AD BD LL 0 NaN NaN left_only

2 AF BF MM 0 AF BF both

So, as above, indicator does the job.

Peter