R help - Feb 2021 - Alternative to mapply to select samples

Dear R-Help,

I created a mapply function to select samples from a dataset but are there
any faster ways to do it by avoiding mapply because it is slow and I have a
larger dataset? My goal is to use more matrix / vector operations and less
in terms of lists (the format of the output can be flexible). Ideally, I
would like to stick to base R methods without the aid of parallel process
or packages. Any ideas will be appreciated!

#A list of a set of data to be selected
bl <- list(list(c(1, 2),c(2, 3), c(3, 4), c(4, 5), c(5, 6), c(6, 7), c(7,
8), c(8, 9)),
         list(c(1, 2, 3), c(2, 3, 4), c(3, 4, 5), c(4, 5, 6), c(5, 6, 7),
c(6, 7, 8)),
         list(c(1, 2, 3, 4, 5), c(2, 3, 4, 5, 6), c(3, 4, 5, 6, 7), c(4, 5,
6, 7, 8), c(5, 6, 7, 8, 9)))
#Number of elements to be selected
kn <- c(5, 4, 3)
#Total number of elements in each set
nb <- c(8, 6, 5)
#This output a list but preferably I would like a matrix
bl_func <- function() mapply(function(x, y, z) {
  x[sample.int(y, z, replace = TRUE)]
}, bl, nb, kn, SIMPLIFY = FALSE)

Best,

Chao
?

	[[alternative HTML version deleted]]

Hi

I am not sure if I understand your function but simple mapply gives you probably
the same result and may be quicker.
> set.seed(111)
> blf <- bl_func()
> set.seed(111)
> blm <- mapply(sample, bl, kn, replace=TRUE)
> all.equal(blf, blm)
[1] TRUE
 
> Cheers
Petr
> -----Original Message-----
> From: R-help <r-help-bounces at r-project.org> On Behalf Of Chao Liu
> Sent: Tuesday, February 2, 2021 3:32 PM
> To: r-help <r-help at r-project.org>
> Subject: [R] Alternative to mapply to select samples
> 
> Dear R-Help,
> 
> I created a mapply function to select samples from a dataset but are there
> any faster ways to do it by avoiding mapply because it is slow and I have a
> larger dataset? My goal is to use more matrix / vector operations and less
> in terms of lists (the format of the output can be flexible). Ideally, I
> would like to stick to base R methods without the aid of parallel process
> or packages. Any ideas will be appreciated!
> 
> #A list of a set of data to be selected
> bl <- list(list(c(1, 2),c(2, 3), c(3, 4), c(4, 5), c(5, 6), c(6, 7),
c(7,
> 8), c(8, 9)),
>          list(c(1, 2, 3), c(2, 3, 4), c(3, 4, 5), c(4, 5, 6), c(5, 6, 7),
> c(6, 7, 8)),
>          list(c(1, 2, 3, 4, 5), c(2, 3, 4, 5, 6), c(3, 4, 5, 6, 7), c(4, 5,
> 6, 7, 8), c(5, 6, 7, 8, 9)))
> #Number of elements to be selected
> kn <- c(5, 4, 3)
> #Total number of elements in each set
> nb <- c(8, 6, 5)
> #This output a list but preferably I would like a matrix
> bl_func <- function() mapply(function(x, y, z) {
>   x[sample.int(y, z, replace = TRUE)]
> }, bl, nb, kn, SIMPLIFY = FALSE)
> 
> Best,
> 
> Chao
> ?
> 
> 	[[alternative HTML version deleted]]
> 
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