[R] Bug? Index output of C functions R_qsort_I and R_qsort_int_I is not modified

[Evangelos Evangelou]

Thanks for your input Bill.

I also realised that the second argument must be initialised to 1:n, which is not mentioned in the documentation. So, if I define
void mysort2i (int *x, int *i, int *n)
{
  R_qsort_int_I(x,i,1,*n);
}

Then

> .C("mysort2i",4:1,integer(4),4L)
[[1]]
[1] 1 2 3 4

[[2]]
[1] 0 0 0 0

[[3]]
[1] 4

but

> .C("mysort2i",4:1,1:4,4L)
[[1]]
[1] 1 2 3 4

[[2]]
[1] 4 3 2 1

[[3]]
[1] 4


________________________________
From: Bill Dunlap <williamwdunlap using gmail.com>
Sent: 16 April 2021 04:50
To: Evangelos Evangelou <ee224 using bath.ac.uk>
Cc: r-help using r-project.org <r-help using r-project.org>
Subject: Re: [R] Bug? Index output of C functions R_qsort_I and R_qsort_int_I is not modified




R_ext/Utils.h:void R_qsort_int_I(int *iv, int *II, int i, int j);

The last 2 arguments are int, not int*.  .C() passes pointers to vectors so you cannot call this function directly from .C().

-Bill

On Thu, Apr 15, 2021 at 3:15 PM Evangelos Evangelou via R-help <r-help using r-project.org<mailto:r-help using r-project.org>> wrote:
Hi all.

Reading the documentation of these two functions
https://cran.r-project.org/doc/manuals/r-release/R-exts.html#Utility-functions<https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fcran.r-project.org%2Fdoc%2Fmanuals%2Fr-release%2FR-exts.html%23Utility-functions&data=04%7C01%7Cee224%40bath.ac.uk%7C10bfc437aa4c4a1de23208d9008ad510%7C377e3d224ea1422db0ad8fcc89406b9e%7C0%7C0%7C637541418550685457%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=vIt2tF%2BtNP%2B8t%2FNmUtNsP0JGRoOyo30jy1hWD%2BQI2vk%3D&reserved=0>
"The ..._I() versions also return the sort.index() vector in I."
I can't find anything in the documentation about sort.index(), but I'm guessing that I is the index that makes the input sorted, as in R's order(). However running the following code on
R version 4.0.5 (2021-03-31) Platform: x86_64-pc-linux-gnu (64-bit)
does not give me that. It just gives me the original input.

Rlib = file.path(Sys.getenv("R_HOME"), "lib", paste0("libR", .Platform$dynlib.ext))
dyn.load(Rlib)
n = 4L
ix = n:1
i = integer(n)
cc = .C("R_qsort_int_I", ix, i, 1L, n)
cc[[2]]

I expect 4 3 2 1, but I get 0 0 0 0. Is this a bug or have I misunderstood something?

Best,
Vangelis

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