Keeping only rows of a data table that appear in another data table r

Asked May 03 '17 at 16:31

Active May 03 '17 at 16:33

Viewed 25 times

Consider the following data table.

dat=data.table(expand.grid(x1=0:6,x2=0:6))

 categoryvector=6
 points = seq(0,categoryvector,by=ceil(((categoryvector - 0)/(5 - 1))))

Which gives:

keepers = expand.grid(x1=points,x2=points)


   x1 x2
1   0  0
2   2  0
3   4  0
4   6  0
5   0  2
6   2  2
7   4  2
8   6  2
9   0  4
10  2  4
11  4  4
12  6  4
13  0  6
14  2  6
15  4  6
16  6  6

How do I keep only the subset of rows in dat which contain a row from keepers?

In the real data frame, dat, there are other columns but I only care to condition on these two.

edited May 03 '17 at 16:33

asked May 03 '17 at 16:31

wolfsatthedoor

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Did you meant `dat[x1 %in% keepers$x1 & x2 %in% keepers$x2]` – akrun May 03 '17 at 16:32
1

@akrun should be fixed – wolfsatthedoor May 03 '17 at 16:34
Hey @akrun, the problem is, I dont want to check uniquely, but jointly. I think in this example its tantamount to the same thing, but not generally – wolfsatthedoor May 03 '17 at 16:34
1

It's just an inner join. `merge(dat, keepers, by = c("x1", "x2"))` – Gregor Thomas May 03 '17 at 16:34
Suggested dupe: [How to join data frames in R (inner, outer, left, right)?](http://stackoverflow.com/q/1299871/903061) – Gregor Thomas May 03 '17 at 16:35
3

Or just `dat[keepers, on = .(x1,x2)]` – akrun May 03 '17 at 16:36

Keeping only rows of a data table that appear in another data table r

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