R help - Sep 2009 - Accumulating results from "for" loop in a list/array

Dear R users,


I would like to accumulate objects generated from 'for' loop to a list
or
array.

To illustrate the problem, arbitrary data set and script is shown below,


x <- data.frame(a =
c(rep("n",3),rep("y",2),rep("n",3),rep("y",2)),
b
c(rep("y",2),rep("n",4),rep("y",3),"n"),
c = c(rep("n",7),rep("y",3)), d c("y",
rep("n",4), rep("y",2), rep("n",3)))

for (i in 1:(dim(x)[2]))  {
         assign(paste("ind", i, sep = ""), which(x[ , i] ==
"y"))
          accum <- c(ind1, ind2, ind3, ind4)
}
> ind1
[1]  4  5  9 10
> ind2
[1] 1 2 7 8 9
> ind3
[1]  8  9 10
> ind4
[1] 1 6 7
> accum
 [1]  4  5  9 10  1  2  7  8  9  8  9 10  1  6  7

Are there any alternative method where the highlighted statement above can
be represented without typing individual objects manually? (as it can be
very tedious with large number of objects; i.e ind1, ind2, ....., ind100)

Also, is there any way to extract individual objects ('ind1' etc) from
'accum'?
> accum[1:length(ind1)]
[1]  4  5  9 10
gives 'ind1', but this may become messy for other objects (like
'ind10')


Highly appreciate for sharing your expertise in solving this problem.

	[[alternative HTML version deleted]]

Steven

I think list() can help you

##########################################
indlist = list()
 for (i in 1:(dim(x)[2]))  {
         indlist[[paste("ind", i, sep = "")]] <- 
which(x[ , i] == "y")
 }
accum = unlist(indlist)
print(indlist$ind1)
###########################################

Schalk Heunis



On Fri, Sep 11, 2009 at 7:52 AM, Steven Kang <stochastickang at gmail.com>
wrote:
> Dear R users,
>
>
> I would like to accumulate objects generated from 'for' loop to a
list or
> array.
>
> To illustrate the problem, arbitrary data set and script is shown below,
>
>
> x <- data.frame(a =
c(rep("n",3),rep("y",2),rep("n",3),rep("y",2)),
b >
c(rep("y",2),rep("n",4),rep("y",3),"n"),
c = c(rep("n",7),rep("y",3)), d > c("y",
rep("n",4), rep("y",2), rep("n",3)))
>
> for (i in 1:(dim(x)[2])) ?{
> ? ? ? ? assign(paste("ind", i, sep = ""), which(x[ , i]
== "y"))
> ? ? ? ? ?accum <- c(ind1, ind2, ind3, ind4)
> }
>
>> ind1
> [1] ?4 ?5 ?9 10
>> ind2
> [1] 1 2 7 8 9
>> ind3
> [1] ?8 ?9 10
>> ind4
> [1] 1 6 7
>> accum
> ?[1] ?4 ?5 ?9 10 ?1 ?2 ?7 ?8 ?9 ?8 ?9 10 ?1 ?6 ?7
>
> Are there any alternative method where the highlighted statement above can
> be represented without typing individual objects manually? (as it can be
> very tedious with large number of objects; i.e ind1, ind2, ....., ind100)
>
> Also, is there any way to extract individual objects ('ind1' etc)
from
> 'accum'?
>
>> accum[1:length(ind1)]
> [1] ?4 ?5 ?9 10
> gives 'ind1', but this may become messy for other objects (like
'ind10')
>
>
> Highly appreciate for sharing your expertise in solving this problem.
>
> ? ? ? ?[[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.
>

Steven Kang schrieb:
> Dear R users,
>
>
> I would like to accumulate objects generated from 'for' loop to a
list or
> array.
>
> To illustrate the problem, arbitrary data set and script is shown below,
>
>
> x <- data.frame(a =
c(rep("n",3),rep("y",2),rep("n",3),rep("y",2)),
b >
c(rep("y",2),rep("n",4),rep("y",3),"n"),
c = c(rep("n",7),rep("y",3)), d > c("y",
rep("n",4), rep("y",2), rep("n",3)))
>
> for (i in 1:(dim(x)[2]))  {
>          assign(paste("ind", i, sep = ""), which(x[ ,
i] == "y"))
>           accum <- c(ind1, ind2, ind3, ind4)
> }
>
>   
Using "for" loops is not idiomatic; I tend to use them only if I
really
need intermediate results.

res <- apply(x, 2, function(answer) which(answer == "y"))

names(res) <- paste("ind", 1:ncol(x), sep="")
>> ind1
>>     
> [1]  4  5  9 10
>   
>> ind2
>>     
> [1] 1 2 7 8 9
>   
>> ind3
>>     
> [1]  8  9 10
>   
>> ind4
>>     
> [1] 1 6 7
>   
>> accum
>>     
>  [1]  4  5  9 10  1  2  7  8  9  8  9 10  1  6  7
>
> Are there any alternative method where the highlighted statement above can
> be represented without typing individual objects manually? (as it can be
> very tedious with large number of objects; i.e ind1, ind2, ....., ind100)
>
>   
/I think you are looking for unlist()./
> Also, is there any way to extract individual objects ('ind1' etc)
from
> 'accum'?
>
>   
Well, I think they are not objects by themselves anymore. You may want 
to give the vector elements individual names based on their origin and 
then extract appropriate elements by string matching.