What is wrong with this FOR-loop?

Hi,

I guess that res[i,j] needs integers as indexes.

I would try it like this:

(corrected)

run_rows<-seq(0,1,0.05)
run_cols<-seq(0.3,0.6,0.05)

res<-matrix(NA,length(run_rows),length(run_cols))

for(i in 1:length(run_rows))
{
    for(j in 1:length(run_cols))
    {
        res[i,j]=run_rows[i]+run_cols[j]
    }
}

Thank you,
Serguei

Christian

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Christian Hennig
University College London, Department of Statistical Science
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chrish at stats.ucl.ac.uk, www.homepages.ucl.ac.uk/~ucakche

Hi, I have a more complex example, but the problem boils down to this 
FOR-loop not filling in the res-matrix

for(i in run_rows)
{
     for(j in run_cols)
     {
         res[i,j]=i+j

have a look at what i and j are in such a loop:

 > for(i in run_rows){
+ print(i)
+ }
[1] 0
[1] 0.05
[1] 0.1
[1] 0.15
[1] 0.2
[1] 0.25

  - and then you are trying to fill res[0.05,.3] and so on. Its not 
going to work!

You probably want something like:

  for(i in 1:length(run_rows)){

so that i is 1,2,3,....

  then you do:

  res[i,j] = run_rows[i] + run_cols[j]

  within your loop...

  ...which in fact can be done in one line, but you need to learn about 
matrix indexing first!

Barry

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run_rows<-seq(0,1,0.05)
run_cols<-seq(0.3,0.6,0.05)

res<-matrix(NA,length(run_rows),length(run_cols))

for(i in 1:length(run_rows))
{
   for(j in 1:length(run_cols))
   {
       res[i,j]=run_rows[i]+run_cols[j]
   }
}

Or the one-liner:

res = outer(run_rows,run_cols,"+")

but maybe its good to learn about array indexing first...

Barry

your indexing is wrong; another way to achieve the same result is

outer(run_rows, run_cols, "+")


I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://www.med.kuleuven.be/biostat/
     http://www.student.kuleuven.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "Serguei Kaniovski" <kaniovsk at wifo.ac.at>
To: <r-help at stat.math.ethz.ch>
Sent: Monday, December 05, 2005 12:47 PM
Subject: [R] What is wrong with this FOR-loop?

Hi, I have a more complex example, but the problem boils down to 
this
FOR-loop not filling in the res-matrix

run_rows<-seq(0,1,0.05)
run_cols<-seq(0.3,0.6,0.05)

res<-matrix(NA,length(run_rows),length(run_cols))

for(i in run_rows)
{
    for(j in run_cols)
    {
        res[i,j]=i+j
        #niether the above, nor res[[i,j]]=i+j work, why?
    }
}

Thank you,
Serguei

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