r - remove duplicate values based on 2 columns

Question

I want to remove duplicate values based upon matches in 2 columns in a dataframe, v2 & v4 must match between rows to be removed.

> df

   v1  v2  v3   v4  v5
1  7   1   A  100  98 
2  7   2   A  100  97
3  8   1   C   NA  80
4  8   1   C   78  75
5  8   1   C   78  62
6  9   3   C   75  75

For a result of

> df

   v1  v2  v3   v4  v5
1  7   1   A  100  98 
2  8   1   C   NA  80
3  8   1   C   78  75
4  9   3   C   75  75

I know I want something like:

df[!duplicated(df[v2] && df[v4]),] 

but this doesn't work.

This question is specifically about dataframes, for those who have a data.table, see Filtering out duplicated/non-unique rows in data.table.

Answer 1

This will give you the desired result:

df [!duplicated(df[c(1,4)]),]