[R] distributing the values of data frame to a vector based on......

[Daniel O'Shea]

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)