以最快的方式用数组索引按降序打印矩阵的排序元素 [英] Printing the sorted elements of a matrix in descending order with array indices in the fastest fashion

问题描述

这似乎是一个简单的问题，但我无法快速进行此操作.

This seems like a simple problem but I am having trouble doing this in a fast manner.

说我有一个矩阵，我想对该矩阵排序并按降序存储元素的索引.有没有一种快速的方法可以做到这一点?现在，我正在提取最大值，将结果存储，将其更改为-2，然后在for循环中提取下一个最大值.这可能是最无效率的方法.

Say I have a matrix and I want to sort this matrix and store the indices of the elements in descending order. Is there a quick way to do this? Right now, I am extracting the maximum, storing the result, changing it to -2, and then extracting the next maximum in a for loop. Which is probably the most inefficient way to do it.

我的问题实际上需要我处理20,000 X 20,000矩阵.内存不是问题.关于最快的方法的任何想法都将很棒.

My problem actually requires me to work on a 20,000 X 20,000 matrix. Memory is not an issue. Any ideas about the fastest way to do it would be great.

例如，如果我有一个矩阵

For example if I have a matrix

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

我希望结果按降序指示数字:

I want the result to indicate the numbers in descending order:

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

推荐答案

以下是可能的data.table解决方案

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

---

编辑:基本R替代项

---

Edit: a 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

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