R help - Oct 2010 - for loop

Dear all,
  I have a function f(x)  which return a list as result.

$T1
[1] 0.03376190
$T2
[1] 0.04725
$T3
[1] 0.3796071
$T4
[1] 0.3713452
$T5
[1] 0.4523651
$T6
[1] 0.4575873

  I now find the result for a vector of x values at one time. I want to
store the reuslt
for each xi value in a column of a matrix

x <- seq(0,1, by=0.1)
result <- matrix(0, nrow=6, ncol=length(x))

for (i in 1:length(x)){result[,i] <- f(x[i])}

It is not working. Can some help me.
Thank you very much!
                        Hannah

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Dear Hannah,

Well one issue is that you are trying to assign a list to a matrix
column.  This is a hazardous move, and may well be your problem.  Try:
 lapply(x, f)

that should give you some nice results, and can probably be fairly
easily converted to a matrix if you want.  It is really hard to give
you more help without having f() and without the exact details of what
went wrong or the error message (if there was one).

Best regards,

Josh



On Thu, Oct 14, 2010 at 2:53 PM, li li <hannah.hlx at gmail.com>
wrote:
> Dear all,
> ?I have a function f(x) ?which return a list as result.
>
> $T1
> [1] 0.03376190
> $T2
> [1] 0.04725
> $T3
> [1] 0.3796071
> $T4
> [1] 0.3713452
> $T5
> [1] 0.4523651
> $T6
> [1] 0.4575873
>
> ?I now find the result for a vector of x values at one time. I want to
> store the reuslt
> for each xi value in a column of a matrix
>
> x <- seq(0,1, by=0.1)
> result <- matrix(0, nrow=6, ncol=length(x))
>
> for (i in 1:length(x)){result[,i] <- f(x[i])}
>
> It is not working. Can some help me.
> Thank you very much!
> ? ? ? ? ? ? ? ? ? ? ? ?Hannah
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/

On 10/14/2010 2:53 PM, li li wrote:
> Dear all,
>    I have a function f(x)  which return a list as result.
>
> $T1
> [1] 0.03376190
> $T2
> [1] 0.04725
> $T3
> [1] 0.3796071
> $T4
> [1] 0.3713452
> $T5
> [1] 0.4523651
> $T6
> [1] 0.4575873
>
>    I now find the result for a vector of x values at one time. I want to
> store the reuslt
> for each xi value in a column of a matrix
>
> x<- seq(0,1, by=0.1)
> result<- matrix(0, nrow=6, ncol=length(x))
>
> for (i in 1:length(x)){result[,i]<- f(x[i])}
>
> It is not working. Can some help me.
> Thank you very much!
>                          Hannah
In order to test my solution, I needed a function that returned 
something of the structure you had.

f <- function(x) {
	r <- as.list(rnorm(6))
	names(r) <- paste("T",1:6,sep="")
	r
}

Using that, you can replace the for loop with:

for (i in 1:length(x)){result[,i] <- unlist(f(x[i]))}

The problem is that f returns a list; you can only put a vector in part 
of a matrix.  unlist() takes care of that conversion.

-- 
Brian S. Diggs, PhD
Senior Research Associate, Department of Surgery
Oregon Health & Science University

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Hi, 

 

I know this is probalby a very trivial thing to do for most of the R users, but
since I just strated using it I have some problems....

 

I have a data.frame with a field called "razred". This field has
values from 1 up to 15.

Is it possible to create a for loop that would create a new data frame for each
of the "razred" values.

 

Thanks for the help, m

 

 

 


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On Oct 30, 2010, at 2:07 PM, Matev? Pavli? wrote:
> Hi,
>
> I know this is probalby a very trivial thing to do for most of the R  
> users, but since I just strated using it I have some problems....
>
> I have a data.frame with a field called "razred". This field has
> values from 1 up to 15.
>
> Is it possible to create a for loop that would create a new data  
> frame for each of the "razred" values.
The R-way would be to use the split function and leave the result in a  
list to which the same operation could be also repeatedly performed  
using lapply.

?split

And take a look at the fourth example applying split to the builtin  
airquality dataframe.

The plyr package also provides functions on dataframes.

-- 

David Winsemius, MD
West Hartford, CT

Thanks for the suggestions.
I add some more detail to clarify:

h=matrix(nrow=1,ncol=22)

In my data h is: 
(0.25  0.25  0  0  0  0  -0.25  -0.25  -0.25  -0.25  -0.5  -0.5  0  0.25  0.25 
0.25  0.25  0.25  0.25  0.25  0.25  0.25)



xx<-seq(0,1,0.00005)

v=matrix(nrow=20001,ncol=22)
vv=matrix(nrow=20001,ncol=22)
for (y in 1:20001) {
v[y,22]=h[1,22]
}
vv[20001,22]=v[20001,22]
for(k in 21:1) {
 for(j in 20001:2) {
   vv[j-1,k+1]=min(xx[j-1]*v[j-1,k+1],vv[j,k+1])
   v[j,k]=h[1,k]+vv[j-1,k+1]
 }
vv[20001,k]=v[20001,k]
}



The idea of using Rcpp seems to be good. Having never used this package will
give a look.
Somewhere I read an example like this:


for (i in 1:R) {
  res[i]<-f()
  NULL
}

where f() is a function, but I don't how can I trasform my code:
vv[j-1,k+1]=min(xx[j-1]*v[j-1,k+1],vv[j,k+1])
v[j,k]=h[1,k]+vv[j-1,k+1]
in a function








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