[R] random sample from arrays

[Joris Meys]

Don't know what exactly you're trying to do, but you make a matrix
with 11 columns and 50 rows, then treat it as a vector. On top of
that, you try to fill 50 rows/columns with 50 values. Off course that
doesn't work. Did you check the warning messages when running the
code?

Either do :

 for(i in c(1:11)){
    set[,i] <-sample(x,50)
    print(c(i,"->", set), quote = FALSE)
   }

or

 for(i in c(1:50)){
    set[i,] <-sample(x,11)
    print(c(i,"->", set), quote = FALSE)
   }

Or just forget about the loop altogether and do :

set <- replicate(11,sample(x,50))
or
set <- t(replicate(50,sample(x,11)))

cheers

On Thu, Jul 8, 2010 at 8:04 AM, Assa Yeroslaviz <frymor at gmail.com> wrote:
> Hello R users,
>
> I'm trying to extract random samples from a big array I have.
>
> I have a data frame of over 40k lines and would like to produce around 50
> random sample of around 200 lines each from this array.
>
> this is the matrix
>          ID xxx_1c xxx__2c xxx__3c xxx__4c xxx__5T xxx__6T xxx__7T xxx__8T
> yyy_1c yyy_1c _2c
> 1 A_512  2.150295  2.681759  2.177138  2.142790  2.115344  2.013047
> 2.115634  2.189372  1.643328  1.563523
> 2 A_134 12.832488 12.596373 12.882581 12.987091 11.956149 11.994779
> 11.650336 11.995504 13.024494 12.776322
> 3 A_152  2.063276  2.160961  2.067549  2.059732  2.656416  2.075775
> 2.033982  2.111937  1.606340  1.548940
> 4 A_163  9.570761 10.448615  9.432859  9.732615 10.354234 10.993279
> 9.160038  9.104121 10.079177  9.828757
> 5 A_184  3.574271  4.680859  4.517047  4.047096  3.623668  3.021356
> 3.559434  3.156093  4.308437  4.045098
> 6 A_199  7.593952  7.454087  7.513013  7.449552  7.345718  7.367068
> 7.410085  7.022582  7.668616  7.953706
> ...
>
> I tried to do it with a for loop:
>
> genelist <- read.delim("/user/R/raw_data.txt")
> rownames(genelist) <- genelist[,1]
> genes <- rownames(genelist)
>
> x <- 1:40000
> set <- matrix(nrow = 50, ncol = 11)
>
> for(i in c(1:50)){
>    set[i] <-sample(x,50)
>    print(c(i,"->", set), quote = FALSE)
>    }
>
> which basically do the trick, but I just can't save the results outside the
> loop.
> After having the random sets of lines it wasn't a problem to extract the
> line from the arrays using subset.
>
> genSet1 <-sample(x,50)
> random1 <- genes %in% genSet1
> subsetGenelist <- subset(genelist, random1)
>
>
> is there a different way of creating these random vectors or saving the loop
> results outside tjhe loop so I cn work with them?
>
> Thanks a lot
>
> Assa
>
>        [[alternative HTML version deleted]]
>
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> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Joris Meys
Statistical consultant

Ghent University
Faculty of Bioscience Engineering
Department of Applied mathematics, biometrics and process control

tel : +32 9 264 59 87
Joris.Meys at Ugent.be
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