I have a matrix with two columns of the following form:
1 349
1 393
1 392
4 459
3 49
3 32
2 94
I would like to sort this matrix in increasing order based on the first column but I would like to keep the corresponding values in the second column.
The output would look like this:
1 349
1 393
1 392
2 94
3 49
3 32
4 459
This question is related to
r
Creating a data.table
with key=V1
automatically does this for you. Using Stephan's data foo
> require(data.table)
> foo.dt <- data.table(foo, key="V1")
> foo.dt
V1 V2
1: 1 349
2: 1 393
3: 1 392
4: 2 94
5: 3 49
6: 3 32
7: 4 459
If your data is in a matrix named foo
, the line you would run is
foo.sorted=foo[order[foo[,1]]
The accepted answer works like a charm unless you're applying it to a vector. Since a vector is non-recursive, you'll get an error like this
$ operator is invalid for atomic vectors
You can use [
in that case
foo[order(foo["V1"]),]
Be aware that if you want to have values in the reverse order, you can easily do so:
> example = matrix(c(1,1,1,4,3,3,2,349,393,392,459,49,32,94), ncol = 2)
> example[order(example[,1], decreasing = TRUE),]
[,1] [,2]
[1,] 4 459
[2,] 3 49
[3,] 3 32
[4,] 2 94
[5,] 1 349
[6,] 1 393
[7,] 1 392
Source: Stackoverflow.com