Comparing two similar dataframes and finding different values between them

Question

This is a seemingly basic question, I apologize in advance if this is a duplicate question. I looked around and didn\'t see anything.

I have two dataframes full of

Answer 1

You could do:

df2[mapply(function(x,y)   x%in%y ,df1,df2)]<-NA
     x    y
1 <NA>    l
2 <NA>    m
3    j <NA>
4    k <NA>

This affects df2 directly, better have a copy of it.

Explanation:
mapply() is used to have the %in% applied between the first column of df1 and df2, and then the second and so on if there were more.
This gives:

> mapply(function(x,y)   x%in%y,df1,df2)
         x     y
[1,]  TRUE FALSE
[2,]  TRUE FALSE
[3,] FALSE  TRUE
[4,] FALSE  TRUE

TRUE are the values that matched, these are the want we want to change into NA's.