Home/ Questions/Q 4328892
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-21T09:44:56+00:00

I’m writing an R package that manipulates Matrices in C. Currently, the matrices returned

  • 0

I’m writing an R package that manipulates Matrices in C. Currently, the matrices returned to R have numbers for the row/column names. I would rather assign my own row/column names when modifying the object in C.

I’ve googled around for about an hour, but haven’t found a good solution yet. The closest I’ve found is dimnames, but I want to name each column, not just the two dimensions. The matrices get larger than 4×4, below is just a small example of what I want to do.

The number of rows is 4^x where X is the length of the row name

Current
     [,1] [,2] [,3] [,4]
[1,] 0.20 0.00 0.00 0.80
[2,] 0.25 0.25 0.25 0.25
[3,] 0.25 0.25 0.25 0.25
[4,] 1.00 0.00 0.00 0.00
[5,] 0.20 0.00 0.00 0.80
[6,] 0.25 0.25 0.25 0.25
[7,] 0.25 0.25 0.25 0.25
[8,] 1.00 0.00 0.00 0.00
[9,] 0.20 0.00 0.00 0.80
[10,] 0.25 0.25 0.25 0.25
[11,] 0.25 0.25 0.25 0.25
[12,] 1.00 0.00 0.00 0.00
[13,] 0.20 0.00 0.00 0.80
[14,] 0.25 0.25 0.25 0.25
[15,] 0.25 0.25 0.25 0.25
[16,] 1.00 0.00 0.00 0.00

Desired
     [A] [C] [G] [T]
 [AA] 0.20 0.00 0.00 0.80
 [AC] 0.25 0.25 0.25 0.25
 [AG] 0.25 0.25 0.25 0.25
 [AT] 1.00 0.00 0.00 0.00
 [CA] 0.20 0.00 0.00 0.80
 [CC] 0.25 0.25 0.25 0.25
 [CG] 0.25 0.25 0.25 0.25
 [CT] 1.00 0.00 0.00 0.00
 [GA] 0.20 0.00 0.00 0.80
 [GC] 0.25 0.25 0.25 0.25
 [GG] 0.25 0.25 0.25 0.25
 [GT] 1.00 0.00 0.00 0.00
 [TA] 0.20 0.00 0.00 0.80
 [TC] 0.25 0.25 0.25 0.25
 [TG] 0.25 0.25 0.25 0.25
 [TT] 1.00 0.00 0.00 0.00
Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    As Jim said, this is much easier to do in R. I’m passing the names into the C function via the nam argument.

    #include <Rinternals.h>
SEXP myMat(SEXP nam) {
  /*PrintValue(nam);*/
  SEXP ans, dimnames;
  PROTECT(ans = allocMatrix(REALSXP, length(nam), length(nam)));
  PROTECT(dimnames = allocVector(VECSXP, 2));
  SET_VECTOR_ELT(dimnames, 0, nam);
  SET_VECTOR_ELT(dimnames, 1, nam);
  setAttrib(ans, R_DimNamesSymbol, dimnames);
  UNPROTECT(2);
  return(ans);
}

    If you put that code in a file called myMat.c, you can test it via the line below. I’m using Ubuntu, so you will have to change myMat.so to myMat.dll if you’re on Windows.

    R CMD SHLIB myMat.c
Rscript -e 'dyn.load("myMat.so"); .Call("myMat", c("A","C","G","T"))'
    • 0