CODEWITHSUNDEEP
r
Ignacio
Ignacio

Reputation: 7928

Subset a data frame based on another

I have two data frames, x and y.

x<-data.frame(id=c(1,2,3,4,5), g=c(21,52,43,94,35))
y<-data.frame(id=c(3,4,7), u=c(55, 77, 99))

I want to subset x to include only the observations with "IDs" that are also in y.

What is the best way of doing this?

Thanks!

Upvotes: 2

Views: 7769

Answers (2)

pbot
pbot

Reputation: 141

The accepted answer only works because the values 3 and 4 in x$id happen to be located in rows 3 and 4. The wrong answer will be obtained, for example, if: 

x<-data.frame(id=c(1,3,2,4,5), g=c(21,52,43,94,35))
x[intersect(x$id, y$id),]
  id  g
3  2 43
4  4 94

The following will work properly, regardless of the position of the common elements:

x[is.element(x$id,intersect(x$id,y$id)),]

Upvotes: 3

Jilber Urbina
Jilber Urbina

Reputation: 61154

Use setdiff to exclude observations appearing in both df

> x[setdiff(x$id, y$id),]  
  id  g
1  1 21
2  2 52
5  5 35

Use merge to include observations present in both df

> merge(x, y)
  id  g  u
1  3 43 55
2  4 94 77

or looking for this subset?

> x[intersect(x$id, y$id),]
  id  g
3  3 43
4  4 94

Upvotes: 6

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