Sort one matrix based on another matrix

Question

I'm trying to put the rows of one matrix in the same order as the rows of another matrix of the same dimension. However I can't quite figure out how to do this without an explicit loop. It seems I should be able to do this with subsetting and an apply or Map function, but I can't figure out how to do it. Here's a toy example: ``` sortMe <- matrix(rnorm(6), ncol=2) sortBy <- matrix(c(2,1,3, 1,3,2), ncol=2) sorted <- sortMe for (i in 1:ncol(sortMe)) { sorted[,i] <- sortMe[,i][sortBy[,i]] } ``` Using this method, the resulting `sorted` matrix contains the values from `sortMe` sorted in the same order as the `sortBy` matrix. Any idea how I'd do this without the loop?

Accepted Answer

This (using a two-column integer matrix to index the matrix's two dimensions) should do the trick:

```
sorted <- sortMe
sorted[] <- sortMe[cbind(as.vector(sortBy), as.vector(col(sortBy)))]
```

Sort one matrix based on another matrix

Solution

Problem