r - Printing the sorted elements of a matrix in descending order with array indices in the fastest fashion -

this seems simple problem having trouble doing in fast manner.

say have matrix , want sort matrix , store indices of elements in descending order. there quick way this? right now, extracting maximum, storing result, changing -2, , extracting next maximum in loop. inefficient way it.

my problem requires me work on 20,000 x 20,000 matrix. memory not issue. ideas fastest way great.

for example if have matrix

>m<-matrix(c(1,4,2,3),2,2) >m      [,1] [,2] [1,]    1    2 [2,]    4    3 

i want result indicate numbers in descending order:

 row  col val  2    1   4  2    2   3  1    2   2  1    1   1 

here's possible data.table solution

library(data.table) rows <- nrow(m) ; cols <- ncol(m) res <- data.table(                   row = rep(seq_len(rows), cols),                    col = rep(seq_len(cols), each = rows),                   val = c(m) ) setorder(res, -val) res #    row col val # 1:   2   1   4 # 2:   2   2   3 # 3:   1   2   2 # 4:   1   1   1 

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edit: base r alternative

res <- cbind(         row = rep(seq_len(rows), cols),          col = rep(seq_len(cols), each = rows),         val = c(m) )     res[order(-res[, 3]),] #      row col val # [1,]   2   1   4 # [2,]   2   2   3 # [3,]   1   2   2 # [4,]   1   1   1