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

Bill McNeill (UW) billmcn at u.washington.edu
Sat Dec 13 02:02:04 CET 2008

Thanks for the help.  Data frames are gradually starting to make sense to me.

Here's a related question.  I have two data frames, one looks like this:

> m <- data.frame(class = c("birds", "planes"), feather = c(1,3), jet = c(2,4))
> m
class feather jet
1  birds       1   2
2 planes     3   4

and the other looks like this

> d1 <- data.frame(jet = c(10), feather = c(20))
> d1
jet feather
1   10       20

I want to multiply every value in m by the corresponding value in d1.
I want to do this for both rows, so that I end up with

class        feather        jet
1 birds     1*20 = 20    2*10 = 20
2 planes  3*20 = 60    4*10 = 40

As before, the trick is to align numbers by the data frame labels
"feather", "jet", etc. where those columns may appear in different
orders in m and d1.  However, it doesn't seem like merge is
applicable, because here I'm trying to merge on data frame labels
instead of on values in a column of a data frame.  In any event, I
haven't been able to figure out how to do it.

On Wed, Dec 10, 2008 at 6:51 PM, Gabor Grothendieck
<ggrothendieck at gmail.com> wrote:
>
> You probably want Marc's solution but just in case note that zoo's merge
> supports zero fill which means that if you represented the two as zoo
> objects whose "times" are cat, dog, ...  then we would have:
>
>
> File1 <- "type    n
> dog        2
> cat        4
> horse    6"
>
> File2 <- "type    n
> horse    1
> dog        3
> cat        9
> mouse 11"
>
> library(zoo)
>
>
> z <- merge(z1, z2, fill = 0)
> zz <- z[,1] * z[,2]
>
> Also note that coredata(zz) and time(zz) extract the data and times
> respectively.
>
>
> On Wed, Dec 10, 2008 at 6:17 PM, Bill McNeill (UW)
> <billmcn at u.washington.edu> 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.
> > --
> > Bill McNeill
> > http://staff.washington.edu/billmcn/index.shtml
> >
> >        [[alternative HTML version deleted]]
> >
> > ______________________________________________
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