R help - Feb 2007 - Matrix manipulation

Hi, let's say I have this

A = matrix(c(1, 2, 4), nrow=1)
colnames(A)=c("YOO1", "YOO2", "YOO3")

# ie
#      YOO1 YOO2 YOO3
#[1,]    1    2    4

HELLO <- NULL
HELLO$YOO1="BOO"
HELLO$YOO2="BOO"
HELLO$YOO3="HOO"

and I want a matrix that will sum my categorization.. how can I do it
efficiently without any loop?

#ie   BOO   HOO
#[1,]  3         4

Thanks a lot!
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Hi, let's say I have this

A = matrix(c(1, 2, 4), nrow=1)
colnames(A)=c("YOO1", "YOO2", "YOO3")

# ie
#      YOO1 YOO2 YOO3
#[1,]    1    2    4

HELLO <- NULL
HELLO$YOO1="BOO"
HELLO$YOO2="BOO"
HELLO$YOO3="HOO"

and I want a matrix that will sum my categorization.. how can I do it
efficiently without any loop?

#ie   BOO   HOO
#[1,]  3         4

Thanks a lot!
-- 
View this message in context:
http://www.nabble.com/Matrix-manipulation-tf3223618.html#a8953808
Sent from the R help mailing list archive at Nabble.com.

> Hi, let's say I have this
> 
> A = matrix(c(1, 2, 4), nrow=1)
> colnames(A)=c("YOO1", "YOO2", "YOO3")
Why do you need A to be a matrix and not simply a vector?
> 
> # ie
> #      YOO1 YOO2 YOO3
> #[1,]    1    2    4
> 
> HELLO <- NULL
> HELLO$YOO1="BOO"
> HELLO$YOO2="BOO"
> HELLO$YOO3="HOO"
> 
Why do you need HELLO to be a list and not simply a character vector?
> and I want a matrix that will sum my categorization.. how can I do it
> efficiently without any loop?
> 
> #ie   BOO   HOO
> #[1,]  3         4
> 
Anyway, here is a solution:

x <- tapply(A, match(unlist(HELLO), unique(unlist(HELLO))), sum)
names(x) <- unique(unlist(HELLO))
x

HTH,
Giovanni

-- 

Giovanni Petris  <GPetris at uark.edu>
Associate Professor
Department of Mathematical Sciences
University of Arkansas - Fayetteville, AR 72701
Ph: (479) 575-6324, 575-8630 (fax)
http://definetti.uark.edu/~gpetris/