Is there a known way to build a macro that creates a dynamically sized array?

Question

I'd like to be able to write a command that essentially takes two arguments, the number of rows and the number of columns, creates an array of the specified dimensions, and then allows for a variable number of arguments as entries in the array.

I have tried to write such a command myself simply using nested conditionals, but quickly realized that I don't have a strong enough understanding of LaTeX yet to know if variable argument commands are even possible. Thus, I certainly don't understand how to build one yet.

It's possible this might be a silly task, but at the very least I'd like to try to build such a thing or know why it cannot be done.

Answer 1

This not use any macro and need compilation with knitr, but it is relatively simple to type and have the advantage that make R matrices form any sequence (vector) or a data frame is very easy.

---

Example.Rnw file:

---

\documentclass{article}
\begin{document}
<<echo=F>>=
library(xtable)
@
<<printmatrix,include=FALSE>>=
M <- function(x=c(1,2,3),y=1){
  z <- xtableMatharray(matrix(x,nrow=y), digits = 2, auto = F)
  print(z)
  }
W <- M()
@
Default matrix:
[A_{1\times 3}=\left[\Sexpr{W}\right]]
Custom matrices:
<<foo,include=FALSE>>=
W <- M(x=c(1.348,2,3.555,4.7800,5,6,7,8),y=2)
@
[A_{2\times 4}=\left[\Sexpr{W}\right]]
<<bah,include=FALSE>>=
W <- M(x=rnorm(25,2,1),y=5)
@
[A_{5\times 5}=\left[\Sexpr{W}\right]]
<<baz,include=FALSE>>=
W <- M(x=c("foo","bar","baz","end"),y=2)
@
[A_{2\times 2}=\left[\Sexpr{W}\right]]
\end{document}

Answer 2

Do you really want to say something like the following?

\makematrix{2}{5}{1}{3}{7}{-1}{2}{0}{-3}{3}{4}{5}

According to your question this should be the input style you want. Maybe it could be improved by using line breaks

\makematrix{2}{5}
  {1}{3}{7}{-1}{2}
  {0}{-3}{3}{4}{5}

but I don't think it's a great improvement over

\begin{bmatrix}
  1 &  3 & 7 & -1 & 2 \\
  0 & -3 & 3 &  4 & 5
\end{bmatrix}

Do you?

OK, it's not the style CAS software uses. Can we do as follows?

\makematrix{1,3,7,-1,2;0,-3,3,4,5}

Certainly so. The optional argument to \makematrix sets the delimiters (default b; change it if you like p by default); the mandatory argument contains the matrix entries, rows separated by semicolons, entries in the same row by commas.

\documentclass{article}
\usepackage{amsmath}
\ExplSyntaxOn
\NewDocumentCommand{\makematrix}{O{b}m}
 {
  \hpecoraro_matrix_make:nn { #1 } { #2 }
 }
\seq_new:N \l__hpecoraro_matrix_rows_seq
\cs_new_protected:Nn \hpecoraro_matrix_make:nn
 {
  \seq_set_split:Nnn \l__hpecoraro_matrix_rows_seq { ; } { #2 }
  \begin{#1matrix}
  \seq_map_function:NN \l__hpecoraro_matrix_rows_seq __hpecoraro_matrix_dorow:n
  \end{#1matrix}
 }
\cs_new_protected:Nn __hpecoraro_matrix_dorow:n
 {
  \clist_use:nn { #1 } { & } \
 }
\ExplSyntaxOff
\begin{document}
Brackets
[
\makematrix{1,3,7,-1,2;0,-3,3,4,5}
]
Parentheses
[
\makematrix[p]{1,3,7,-1,2;0,-3,3,4,5}
]
\end{document}