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I have a matrix called AS (in R) that collects indices of elements of an array that satisfy a certain condition. This matrix AS, however, is labeled at the top by dim1, dim2, ... which prevent me from using those indexes in typical expressions (cf. picture below). How do I get rid of these dim labels and convert this collection of indices to a regular usable matrix?

Here’s how my dim-labeled matrix looks: enter image description here

And the error if I try to use the indices contained here normally: enter image description here

Note: it’s not the dimensions that are incorrect here since RandPoints[1, ...] is supposed to accept 4 arguments for “...” E.g., it runs fine if I type in RandPoints[1,12,1,1,1], but I rather want that [12,1,1,1] to be supplied by calling the first row of AS as attempted in the picture.

sami.spricht.sprache
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    `colnames(AS) <- NULL` will remove the *column names* in your matrix `AS`, but it's unclear what you are doing with `RandPoints`. Please consider making this question reproducible, both by including **real data** (and code and console output, etc) and not pictures of it (I won't transcribe for you). – r2evans Nov 05 '21 at 20:54
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    Does this answer your question? [How to remove column names from a matrix in R?](https://stackoverflow.com/questions/32658793/how-to-remove-column-names-from-a-matrix-in-r) – manro Nov 05 '21 at 20:55
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    If the question is about the error, then you may need `RandPoints[do.call(cbind, as.list(c(1,AS[2,])))]` – akrun Nov 05 '21 at 20:58
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    Thanks all, @akrun ’s solution worked. – sami.spricht.sprache Nov 05 '21 at 20:59

2 Answers2

1

We could use colnames(my_matrix) <- NULL. Here is an example:

# create a matrix
my_matrix<-matrix(1:30,ncol=3)

# assign names to your matrix
colnames(my_matrix)<-c("dim1", "dim2", "dim3")

# remove the column names
colnames(my_matrix) <- NULL

my_matrix

      [,1] [,2] [,3]
 [1,]    1   11   21
 [2,]    2   12   22
 [3,]    3   13   23
 [4,]    4   14   24
 [5,]    5   15   25
 [6,]    6   16   26
 [7,]    7   17   27
 [8,]    8   18   28
 [9,]    9   19   29
[10,]   10   20   30
TarJae
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1

We may need to pass a matrix of index for subsetting. One option is to convert the matrix row to list with as.list and then cbind so that it becomes a matrix of one row with 5 columns. The 1 is concatenated with the 4 elements of the 2nd row of 'AS' and converted to list

RandPoints[do.call(cbind, as.list(c(1, AS[2,])))]

Or another option is cbind. Note that for matrix/data.frame, the default option is drop = TRUE when there is a single row/column which converts the matrix to a vector. So, change it to drop = FALSE and cbind with 1 (to return 5 column matrix)

 RandPoints[cbind(1, AS[2,, drop = FALSE])]

data

AS <- cbind(dim2 = c(3, 5), dim3 = c(1, 1), dim4 = c(1, 1), dim5 = c(1, 1))
 RandPoints <- array(1:750, dim = c(5, 5, 5, 2, 3))
akrun
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