R language iteratively input a matrix

Question

I'm trying to figure out how to iteratively load a matrix (this form part of a bigger function I can't reproduce here).

Let's suppose that I create a matrix:

 m <- matrix(c(1:9), nrow = 3, ncol = 3)
 m

This matrix can be named "m", "x" or whatsoever. Then, I need to load iteratively the matrix in the function:

 if (interactive() ) { mat <- 
     readline("Your matrix, please: ")
 }

So far, the function "knows" the name of the matrix, since mat returns [1] "m", and is a object listed in ls(). But when I try to get the matrix values, for example through x <- get(mat) I keep getting an error

Error in get(mat) : unused argument (mat)

Can anybody be so kind as to tell me what I'm doing wrong here?

Might want to start here, on how to create an empty matrix and it will also give you some clues on how to accomplish your loop. https://stackoverflow.com/questions/21585721/how-to-create-an-empty-matrix-in-r, also `get` doesn't do what you think it does. — Chuck P, May 22 '20 at 13:52
loading almost anything iteratively in R is probably going to be the wrong way to approach things. in this case why not just : `x = mat` ? — dvd280, May 22 '20 at 13:55

G. Grothendieck · Accepted Answer · 2020-05-22T15:30:38.450

1) Assuming you mean interactive, not iterative,

get_matrix <- function() {
  nr <- as.numeric(readline("how many rows? "))
  cat("Enter space separated data row by row. Enter empty row when finished.\n")
  nums <- scan(stdin())
  matrix(nums, nr, byrow = TRUE)
}
m <- get_matrix()

Here is a test:

> m <- get_matrix()
how many rows? 3
Enter space separated data row by row. Enter empty row when finished.
1: 1 2
3: 3 4
5: 5 6
7: 
Read 6 items

> m
     [,1] [,2]
[1,]    1    2
[2,]    3    4
[3,]    5    6
>

2) Another possibility is to require that the user create a matrix using R and then just give the name of the matrix:

get_matrix2 <- function(envir = parent.frame()) {
  m <- readline("Enter name of matrix: ")
  get(m, envir)
}

Test it:

> m <- matrix(1:6, 3)
> mat <- get_matrix2()
Enter name of matrix: m
> mat
     [,1] [,2]
[1,]    1    4
[2,]    2    5
[3,]    3    6

R language iteratively input a matrix

1 Answers1