# [R] How do I multiply labeled vectors of numbers?

Marc Schwartz marc_schwartz at comcast.net
Thu Dec 11 00:39:24 CET 2008

```on 12/10/2008 05:17 PM Bill McNeill (UW) wrote:
> I'm an R newbie trying to do an operation that seems like it should be very
> simple, but after much playing around with the interface and reading "An
> Introduction to R" I can figure out how to do it.
>
> I have two text files.  File1 contains:
>
> type    n
> dog        2
> cat        4
> horse    6
>
> File2 contains:
>
> type    n
> horse    1
> dog        3
> cat        9
> mouse 11
>
> I want to read both files into R and multiply corresponding values of n so
> that I end up with:
>
> dog       2*3 = 6
> cat        4*9 = 36
> horse    6*1 = 6
> mouse  0*11 = 0
>
> Note that the type rows are not necessarily in the same order in the two
> files, and that a missing type gets a default n = 0 value.
>
> I figure the way to do this is use read.table and do the appropriate
> manipulation of the factors, but I can't figure out what those manipulations
> would be.  Basically I want to use a factor table as a hash table, but I
> haven't been able to figure out how to do this, which makes me think I'm not
> conceptualizing this is the correct R-ish way.
>
> Thanks.

F3 <- merge(F1, F2, by = "type", all = TRUE)

> F3
type n.x n.y
1   cat   4   9
2   dog   2   3
3 horse   6   1
4 mouse  NA  11

# Convert NA's to 0

F3[is.na(F3)] <- 0

> F3
type n.x n.y
1   cat   4   9
2   dog   2   3
3 horse   6   1
4 mouse   0  11

F3\$prod <- F3\$n.x * F3\$n.y

> F3
type n.x n.y prod
1   cat   4   9   36
2   dog   2   3    6
3 horse   6   1    6
4 mouse   0  11    0

See ?merge

HTH,

Marc Schwartz

```

More information about the R-help mailing list