R help - Oct 2007 - distributing the values of data frame to a vector based on......

I am trying to distribute the entries of a data frame (dat) to a vector (water)
based on the values of two other vectors (region and year).  region is also the
columns and year the rows of the data frame (dat).  I can write a bunch of
ifelse statements or I created the for statement below - but there must be a
simpler way??  The for statement probably won't work if I am distributing a
non numeric factor.  Is there a built in function that does this?

Dan O'Shea


##example data
dat<-matrix(c(1,2,3,4,5,6,7,8,9,10,15,16,17,18,19),nrow=3,ncol=5)
colnames(dat)<-1:5
rownames(dat)<-1:3
region<-rep(1:5,3)
year<-rep(1:3,5)


####distributes the data frame values based on column and row identity, but 
###then must perform the apply statement to create a single vector.
water<-vector()
for(i in 1:5){
for(j in 1:3){
water.b<-ifelse(region==region[i]&year==year[j],dat[j,i],0)
water<-cbind(water,water.b)
}}
waterlevel<-apply(water,1,sum)

Does this do what you want?  Another way of doing matrix addressing:
> dat[cbind(year,region)]
 [1]  1  5  9 10 18  3  4  8 16 17  2  6  7 15 19


On 10/23/07, Daniel O'Shea <dan.oshea at dnr.state.mn.us>
wrote:
> I am trying to distribute the entries of a data frame (dat) to a vector
(water) based on the values of two other vectors (region and year).  region is
also the columns and year the rows of the data frame (dat).  I can write a bunch
of ifelse statements or I created the for statement below - but there must be a
simpler way??  The for statement probably won't work if I am distributing a
non numeric factor.  Is there a built in function that does this?
>
> Dan O'Shea
>
>
> ##example data
> dat<-matrix(c(1,2,3,4,5,6,7,8,9,10,15,16,17,18,19),nrow=3,ncol=5)
> colnames(dat)<-1:5
> rownames(dat)<-1:3
> region<-rep(1:5,3)
> year<-rep(1:3,5)
>
>
> ####distributes the data frame values based on column and row identity, but
> ###then must perform the apply statement to create a single vector.
> water<-vector()
> for(i in 1:5){
> for(j in 1:3){
> water.b<-ifelse(region==region[i]&year==year[j],dat[j,i],0)
> water<-cbind(water,water.b)
> }}
> waterlevel<-apply(water,1,sum)
>
> ______________________________________________
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> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?