[R] dificult loop "for"

David Winsemius dwinsemius at comcast.net
Mon Aug 24 03:11:22 CEST 2009

On Aug 23, 2009, at 4:34 PM, Grzes wrote:

> Hi,
> My english isn't briliant and my problem is very dificult to  
> descripe but I
> try ;)
> My first question is: May I write loop "for" like this or similar -  
> for (i
> in sth : sth[length(sth)],  k in sth else : length(sth else) ) -   
> I'd like
> to have two independent conditions in the same loop "for".

Pretty sure the language has not accommodated you for that wish yet.  
You are going to need extra inner "{for"'s and another closing "}"'s.  
That does not seem like a very large barrier to surmount.

Side question/whinge: where did the convention arise to use "sth" as  
an abbreviation? I am a native English-speaker and it still confuses  
me every time I see it. Why not just use "obj" or "item" or  .....?  I  
keep thinking it has to do with a sequence of s-numbered things. (And  
of course "sth else" got R-parsed as a logical construction.)

In R you probably want to use seq_along(e3) anyway, rather than  


 > e3 <- c(1,2,4)
 > for (i in seq_along(e3) ) print(letters[e3[i]])
[1] "a"
[1] "b"
[1] "d"
> My secound question depend on program below. I'd like to write every  
> result
> in matrix but I also want to call my function "odleg" use vector  
> "e3" -
> exactly using values which are inside.
> Can anyone please guide me, how to do that?
> Thanks
> ## Function
> odleg <- function (Xa,Xb,Ya,Yb){
> d <- ((Xa-Xb)^2+(Ya-Yb)^2)^(1/2)
> return (d)
> }
> # Database
> ma=matrix(c(0.51139630,-0.12937287, 0.19530080,
> 0.02273691 
> ,-0.43634186 
> ,-0.01717149,-0.27597035,-0.41732933,-0.15476464,-0.15692965),nrow
> = 5, ncol=2)

untested mods: presumably "me1" has already been defined somewhere else?

e3<- c(1,2,4)

for (i in seq_along(e3) {
                     for (k in seq_along(e3) ) {
for (j in seq_along(e3)] {
                     for (l in seq_along(e3) ){

me1[k,l] = odleg
(nepitabds$points[e3[i],1], nepitabds$points[e3[j],1], nepitabds 
$points[e3[i],2], nepitabds$points[e3[j],2])

The concern I see with the last part of above code is that nepithabds 
$points will need to be a matrix or list that responds properly to  
[n,m] extraction. Is it? That would be possible as I understand the  
rules of data.frames and lists, but it is a bit unusual.

David Winsemius, MD
Heritage Laboratories
West Hartford, CT

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