I have 2 columns in my dataframe namely LocationID and LocationName.

LocationID is not having any NAN entries. However, some of the rows have NaN entires in the LocationName Column. Each Location Name is associated with a unique LocationID.

LocationID and LocationName columns have many duplicated entries in the dataframe.

How do I fill NaN Entries of LocationName column associated with a LocationID if there exists a data point in the dataframe for the same LocationID with no NaN in the LocationName Column.

A sample looks like this:

```
LocationID  LocationName
1   Bengaluru
2   Delhi
3   Mysore
1   
1   
4   Nagpur
2   
2   Delhi
3   Mysore

```