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Jonathan Williams

2005-Oct-05 09:46 UTC

[R] problem accumulating array within a function over loops

Dear R helpers,

I am having trouble with an array inside a loop.

I wish to accumulate the results of a function in an array within
the function, over several loops of a program outside the function.

The problem is that the array seems to re-set at every entry to the
function. Here is an example, so you can see what I mean.

########################################################################
#First, I declare the array and loop control variables
maxrun=3; a=array(NA, c(3,5)); run=0

# Then I define the function "testf"
testf=function(x,y){
print(paste('Run:',run)) #check that the function knows about
"run"
a[run,1:3]=runif(3); a[run,4]=x; a[run,5]=y #collect numbers into array
"a"
print(paste("Row", run, "of a:")); print(a[run,]) #check
what row 'run' of
"a" contains
print("Whole of a:"); print(a) # check what all of "a"
contains
}

#Finally, I loop through "testf" maxrun occasions
for (run in 1:maxrun) testf(run,run*10)
#########################################################################

Here is the output:-

[1] "Run: 1"
[1] "Row 1 of a:"
[1]  0.4637560  0.8872455  0.6421500  1.0000000 10.0000000
[1] "Whole of a:"
          [,1]      [,2]    [,3] [,4] [,5]
[1,] 0.4637560 0.8872455 0.64215    1   10
[2,]        NA        NA      NA   NA   NA
[3,]        NA        NA      NA   NA   NA
[1] "Run: 2"
[1] "Row 2 of a:"
[1]  0.4841261  0.8835118  0.9862266  2.0000000 20.0000000
[1] "Whole of a:"
          [,1]      [,2]      [,3] [,4] [,5]
[1,]        NA        NA        NA   NA   NA
[2,] 0.4841261 0.8835118 0.9862266    2   20
[3,]        NA        NA        NA   NA   NA
[1] "Run: 3"
[1] "Row 3 of a:"
[1]  0.7638856  0.6667588  0.6102928  3.0000000 30.0000000
[1] "Whole of a:"
          [,1]      [,2]      [,3] [,4] [,5]
[1,]        NA        NA        NA   NA   NA
[2,]        NA        NA        NA   NA   NA
[3,] 0.7638856 0.6667588 0.6102928    3   30

You can see that array a correctly collects the numbers at each loop.
But, each successive loop loses the contents of previous loops. I am
hoping to keep the results of each successive loop in "a", so that
after maxrun runs, "a" looks like:-

          [,1]      [,2]    [,3]   [,4] [,5]
[1,] 0.4637560 0.8872455 0.64215      1   10
[2,] 0.4841261 0.8835118 0.9862266    2   20
[3,] 0.7638856 0.6667588 0.6102928    3   30

(I have made this by cutting and pasting from the above output, to show
what I hoped testf would produce).

I am sure I must be making a simple but fundamental error. Would
someone be so kind as to show me what this is and how to correct it?
I have struggled with it for over an hour, without success!!!!!
I am running R 2.1.1 on a Windows 2000 machine.

Thanks, in advance, for your help,

Jonathan Williams

Dimitris Rizopoulos

2005-Oct-05 09:57 UTC

head link

[R] problem accumulating array within a function over loops

try it this way:

a <- array(NA, c(3, 5))
for(i in 1:nrow(a))
    a[i, ] <- c(runif(3), i, i * 10)
a


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: "Jonathan Williams" 
<jonathan.williams at pharmacology.oxford.ac.uk>
To: "Ethz. Ch" <r-help at stat.math.ethz.ch>
Sent: Wednesday, October 05, 2005 11:46 AM
Subject: [R] problem accumulating array within a function over loops

> Dear R helpers,
>
> I am having trouble with an array inside a loop.
>
> I wish to accumulate the results of a function in an array within
> the function, over several loops of a program outside the function.
>
> The problem is that the array seems to re-set at every entry to the
> function. Here is an example, so you can see what I mean.
>
> ########################################################################
> #First, I declare the array and loop control variables
> maxrun=3; a=array(NA, c(3,5)); run=0
>
> # Then I define the function "testf"
> testf=function(x,y){
> print(paste('Run:',run)) #check that the function knows about
"run"
> a[run,1:3]=runif(3); a[run,4]=x; a[run,5]=y #collect numbers into 
> array "a"
> print(paste("Row", run, "of a:")); print(a[run,])
#check what row
> 'run' of
> "a" contains
> print("Whole of a:"); print(a) # check what all of "a"
contains
> }
>
> #Finally, I loop through "testf" maxrun occasions
> for (run in 1:maxrun) testf(run,run*10)
> #########################################################################
>
> Here is the output:-
>
> [1] "Run: 1"
> [1] "Row 1 of a:"
> [1]  0.4637560  0.8872455  0.6421500  1.0000000 10.0000000
> [1] "Whole of a:"
>          [,1]      [,2]    [,3] [,4] [,5]
> [1,] 0.4637560 0.8872455 0.64215    1   10
> [2,]        NA        NA      NA   NA   NA
> [3,]        NA        NA      NA   NA   NA
> [1] "Run: 2"
> [1] "Row 2 of a:"
> [1]  0.4841261  0.8835118  0.9862266  2.0000000 20.0000000
> [1] "Whole of a:"
>          [,1]      [,2]      [,3] [,4] [,5]
> [1,]        NA        NA        NA   NA   NA
> [2,] 0.4841261 0.8835118 0.9862266    2   20
> [3,]        NA        NA        NA   NA   NA
> [1] "Run: 3"
> [1] "Row 3 of a:"
> [1]  0.7638856  0.6667588  0.6102928  3.0000000 30.0000000
> [1] "Whole of a:"
>          [,1]      [,2]      [,3] [,4] [,5]
> [1,]        NA        NA        NA   NA   NA
> [2,]        NA        NA        NA   NA   NA
> [3,] 0.7638856 0.6667588 0.6102928    3   30
>
> You can see that array a correctly collects the numbers at each 
> loop.
> But, each successive loop loses the contents of previous loops. I am
> hoping to keep the results of each successive loop in "a", so
that
> after maxrun runs, "a" looks like:-
>
>          [,1]      [,2]    [,3]   [,4] [,5]
> [1,] 0.4637560 0.8872455 0.64215      1   10
> [2,] 0.4841261 0.8835118 0.9862266    2   20
> [3,] 0.7638856 0.6667588 0.6102928    3   30
>
> (I have made this by cutting and pasting from the above output, to 
> show
> what I hoped testf would produce).
>
> I am sure I must be making a simple but fundamental error. Would
> someone be so kind as to show me what this is and how to correct it?
> I have struggled with it for over an hour, without success!!!!!
> I am running R 2.1.1 on a Windows 2000 machine.
>
> Thanks, in advance, for your help,
>
> Jonathan Williams
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
> 

Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm

vincent@7d4.com

2005-Oct-05 10:10 UTC

head link

[R] problem accumulating array within a function over loops

Jonathan Williams a ??crit :
> maxrun=3; a=array(NA, c(3,5)); run=0
> 
> testf=function(x,y){
> print(paste('Run:',run)) #check that the function knows about
"run"
> a[run,1:3]=runif(3); a[run,4]=x; a[run,5]=y #collect numbers into array
"a"
> }
a outside testf is a "global variable".
a inside testf is a "local variable", ie a variable local to testf().
They are not the same.

As far as I remember, to assign a global variable from inside a
function you have to use the <-- operator.

(By the way, for 2dim arrays, there is also matrix().)

hih
Vincent

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