[R] [Q] Setting elements of a vector
Setzer.Woodrow@epamail.epa.gov
Setzer.Woodrow at epamail.epa.gov
Mon Nov 12 22:48:56 CET 2001
Your code samples from 1:4 20 times with replacement, sums the results,
then assigns the value to all 10000 elements of vec. There is no way
for 'sample' to 'know' that you want 20*10000 samples! Try the
following instead:
> vec <-
apply(matrix(sample(1:4,20*10000,awprob,replace=TRUE),nrow=20),2,sum)
> length(vec)
[1] 10000
> vec[1:10]
[1] 43 38 35 41 35 37 41 42 40 36
> summary(vec)
Min. 1st Qu. Median Mean 3rd Qu. Max.
23.00 35.00 38.00 37.93 41.00 56.00
or
> vec2 <-
tapply(sample(1:4,20*10000,awprob,replace=TRUE),rep(1:10000,rep(20,10000)),sum)
> summary(vec2)
Min. 1st Qu. Median Mean 3rd Qu. Max.
25.00 35.00 38.00 37.99 41.00 57.00
> length(vec2)
[1] 10000
Though on my system (R-1.3.1 on Windows 98) the latter is about 50%
slower.
R. Woodrow Setzer, Jr. Phone:
(919) 541-0128
Experimental Toxicology Division Fax: (919)
541-5394
Pharmacokinetics Branch
NHEERL MD-74; US EPA; RTP, NC 27711
Stefan Meyer
<stem at stem.de> To: r-help at lists.R-project.org
Sent by: cc:
owner-r-help at stat.ma Subject: [R] [Q] Setting elements of a vector
th.ethz.ch
11/12/01 03:35 PM
Hi!
I'm new to R and have problems with the following code:
<code>
awprob<-c(0.4,0.4,0.1,0.1)
awsample<-sample(c(1:4),3,awprob,replace=TRUE)
vec<-vector(mode="numeric",10000)
vec[]<-sum(sample(c(1:4),20,awprob,replace=TRUE))
</code>
My problem: The elements of vec have the same value. How
can I tell R that I want to have a *new* sample for each value
and not 10000 times the same sample?
A for-loop is not a good solution as it made R hang up ...
Thanx alot
Stefan
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