R help - Jul 2003 - create a vector looping over a frame

Hello,

I have a data.frame
> names(popA)
 [1] "Year"   "Series" "Age"    "WM"    
"WF"     "HM"     "HF"     "BM"
 [9] "BF"     "IM"     "IF"     "AM"    
"AF"     "Yr"

how do i loop over a subset of variables in this frame to create a vector of
length equal to the number of variables in the subset such that the vector's
ith element is the result of an aggregate fncn applied to the ith variable?

eg,
sumvar<-c(sum(WM),...,sum(AF))

if i try

for(i in 4:13){
sumVar<- sum(popA[,i])
sumVar2<-c(sumVar) 
}

it returns 
> sumVar2
[1] 287567
> length(sumVar2)
[1] 1

which is only the value at the last spot. i cant quite figure this simple
loop. 

Thanks,

Amer Siddique

> #just to have some data
> testdata<-matrix(rnorm(14*7),ncol=14)
> testframe<-as.data.frame.matrix(testdata)
>
names(testframe)<-c("Year","Series","Age","WM",
"WF","HM","HF","BM","BF","IM","IF","AM","AF","Yr")
> #one way is colSums
> colSums(testframe)[c(3,5,8,10)]
         Age           WF           BM           IM 
 5.024714070  1.974526477  0.004256433 -2.940214886 
> #another way is a for loop
> testvector<-rep(NA,14)
> for (i in 1:14) testvector[i]<-sum(testframe[,i])
> testvector[c(3,5,8,10)]
[1]  5.024714070  1.974526477  0.004256433 -2.940214886
> #there are other ways:)


<snip>
 for(i in 4:13){
sumVar<- sum(popA[,i])
sumVar2<-c(sumVar) 
}
<end snip>
You are replacing sumVar in each iteration of the loop, not creating a new
element.

bob



-----Original Message-----
From: Siddique, Amer [mailto:Amer.Siddique@ssa.gov] 
Sent: Friday, July 18, 2003 4:02 PM
To: 'r-help@stat.math.ethz.ch'
Subject: [R] create a vector looping over a frame 

Hello,

I have a data.frame
> names(popA)
 [1] "Year"   "Series" "Age"    "WM"    
"WF"     "HM"     "HF"     "BM"
 [9] "BF"     "IM"     "IF"     "AM"    
"AF"     "Yr"

how do i loop over a subset of variables in this frame to create a vector of
length equal to the number of variables in the subset such that the vector's
ith element is the result of an aggregate fncn applied to the ith variable?

eg,
sumvar<-c(sum(WM),...,sum(AF))

if i try

for(i in 4:13){
sumVar<- sum(popA[,i])
sumVar2<-c(sumVar) 
}

it returns 
> sumVar2
[1] 287567
> length(sumVar2)
[1] 1

which is only the value at the last spot. i cant quite figure this simple
loop. 

Thanks,

Amer Siddique

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	[[alternative HTML version deleted]]

On Fri, 18 Jul 2003, Siddique, Amer wrote:
> I have a data.frame
>
> > names(popA)
>  [1] "Year"   "Series" "Age"   
"WM"     "WF"     "HM"     "HF"    
"BM"
>  [9] "BF"     "IM"     "IF"    
"AM"     "AF"     "Yr"
>
> how do i loop over a subset of variables in this frame to create a vector
of
> length equal to the number of variables in the subset such that the
vector's
> ith element is the result of an aggregate fncn applied to the ith variable?
>
> eg,
> sumvar<-c(sum(WM),...,sum(AF))
sumvar <- sapply(popA[ ,4:13], sum)

You can use any function, even a user-written one, in place of sum().
When you see the help for  sapply(), remember that a data.frame is
also a list ("inherits" from list).

-  tom blackwell  -  u michigan medical school  -  ann arbor  -