I have a list of dataframe `list=[df1,df2,df3,df4,...df10]`

the dataframe are constructed as following :

```
>df1
col1 col2 col3 col4
Y 2 XX PP
```

I have another dataframe `DATA_SEL `

such that

```
>DATA_SEL
col1 col2 col3 col4
A KK C D
A1 PP C D
...................
..................
```

If the first value (a string) of `col4`

for every dataframe in `list`

(`df1 ,df2,df3....df10`

)does not match with any value of `col2 `

in `DATA_SEL`

, I want to delete that `df`

from `list`

.

How could I possibly do that?

Also if I want to construct a new list, `list2`

where the first value (a string) of `col4`

for every dataframe in `list`

(`df1 ,df2,df3....df10`

) matches with any value of `col2 `

in `DATA_SEL`

, how to do that?

### >Solution :

Use list comprehension with filtering:

```
L = [df1,df2,df3,df4,...df10]
#tested first value of col4
out = [x for x in L if DATA_SEL['col2'].eq(x.at[x.index[0], 'col4']).any()]
#if first row has index == 0
out = [x for x in L if DATA_SEL['col2'].eq(x.at[0, 'col4']).any()]
#tested any value of col4
out = [x for x in L if DATA_SEL['col2'].isin(x['col4']).any()]
```