Hi,
I've got 2 very good solutions, thank you very much. One, from Henrique
Dallazuanna using the library reshape and one line of code - although it will
take me quite some time to understand it. Here it is what he sent:
library(reshape)
xtabs(rowSums(cbind(value.x, value.y), na.rm = TRUE) ~ X1 + X2, merge(melt(m1),
melt(m2), by = c('X1', 'X2'), all = TRUE), exclude = FALSE)
The other is from Phil Spector ( code below) that i can understand quite
easily, although until now to my shame i never quite used factor levels and
their properties and i don't know their uses and possibilities. Until now i
tried to avoid them and transform them in something else (like character
strings).
Again, thanks for all your help,
Monica
----------------------------------------
> Date: Mon, 17 Jan 2011 12:13:09 -0800
> From: spec...@stat.berkeley.edu
> To: pisican...@hotmail.com
> CC: r-help@r-project.org
> Subject: Re: [R] matrix manipulations
>
> Monica -
> Perhaps this small example can demonstrate how factors can
> solve your problem:
>
> > d1 =
> > data.frame(cat=sample(c('cat2','cat5','cat6'),100,replace=TRUE),group=sample(c('land','water'),100,replace=TRUE))
> > d2 =
> > data.frame(cat=sample(c('cat1','cat3','cat4'),100,replace=TRUE),group=sample(c('land','water'),100,replace=TRUE))
> > d1$cat = factor(d1$cat,levels=c('cat1','cat2','cat3','cat4','cat5','cat6'))
> > d2$cat = factor(d2$cat,levels=c('cat1','cat2','cat3','cat4','cat5','cat6'))
> > table(d1$group,d1$cat) + table(d2$group,d2$cat)
>
> cat1 cat2 cat3 cat4 cat5 cat6
> land 14 17 18 22 19 23
> water 19 15 16 11 10 16
>
> This works because when you include all possible levels in a factor, R will
> automatically put zeroes in the right places when you use table():
>
> > table(d1$group,d1$cat)
> cat1 cat2 cat3 cat4 cat5 cat6
> land 0 17 0 0 19 23
> water 0 15 0 0 10 16
> > table(d2$group,d2$cat)
> cat1 cat2 cat3 cat4 cat5 cat6
> land 14 0 18 22 0 0
> water 19 0 16 11 0 0
>
> Hope this helps.
> - Phil Spector
> Statistical Computing Facility
> Department of Statistics
> UC Berkeley
> spec...@stat.berkeley.edu
>
>
>
> On Mon, 17 Jan 2011, Monica Pisica wrote:
>
> >
> > Hi,
> >
> > I am having some difficulties with matrix operations. It is a little hard
> > to explain it so please bear with me. I have a very large data set, large
> > enough that it needs to be split in parts in order to deal with. I can work
> > things on these "parts" but the problem lies in adding together these parts
> > for the final answer.
> >
> > So that been said, let's say that i split the data in 2 parts, 1 and 2.
> > Each part has data belonging to 6 different categories, and each category
> > has 2 different classes, these classes being the same for each category.
> > The classes are called "land" and "water" and each category is labeled
> > "cat1" to "cat6". I am using the command (function) table to tabulate each
> > class for each category, but since i split the data in 2 parts, one part
> > has only some of the 6 categories, and the other some other of the 6
> > categories (and not necessarily exclusive).
> >
> > So let's built some results after i used the table function.
> >
> > m1 <- matrix(c(32, 35, 36, 12, 15, 16), nrow = 2, ncol = 3, byrow = TRUE,
> > dimnames = list(c("land", "water"), c("cat2", "cat5", "cat6")))
> >
> >> m1
> > cat2 cat5 cat6
> > land 32 35 36
> > water 12 15 16
> >
> > m2 <- matrix(c(45, 46, 47, 48, 21, 22, 23, 24), nrow = 2, ncol = 4, byrow =
> > TRUE, dimnames = list(c("land", "water"), c("cat1", "cat2", "cat3",
> > "cat4")))
> >
> >> m2
> > cat1 cat2 cat3 cat4
> > land 45 46 47 48
> > water 21 22 23 24
> >
> > So my end desired result should be a matrix (or a data frame) that has 6
> > columns called cat1 to cat6 and 2 rows labeled land and water, and for the
> > category that appears in both m1 and m2 the end result will be a sum.
> >
> > results will be m3:
> >
> > cat1 cat2 cat3 cat4 cat5 cat6
> > land 45 78 47 48 35 36
> > water 21 34 23 24 15 16
> >
> > To do this i thought in making an empty matrix for each m1 and m2 (called
> > m01 and m02 respectively) with 6 columns and 2 rows, and do a long if else
> > statement in which i match the name of the first column in m1 with the name
> > of the first column in m01 and if they match get the data from m1, if not
> > leave it 0 and so on. Same thing for m2 and m02. This is long and extremely
> > clunky but afterwards i can add m01 with m02 and get my desired result m3.
> > Is there any way i can do this more elegantly? My real data is split in 4
> > parts, but the problem is the same.
> >
> > Thanks for all your inputs, and sorry for this long email, but i didn't
> > know how else i could explain what i wanted to do.
> >
> > Monica
> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
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