In R with a matrix:
one two three four
[1,] 1 6 11 16
[2,] 2 7 12 17
[3,] 3 8 11 18
[4,] 4 9 11 19
[5,] 5 10 15 20
I want to extract the submatrix whose rows have column three = 11. That is:
one two three four
[1,] 1 6 11 16
[3,] 3 8 11 18
[4,] 4 9 11 19
I want to do this without looping. I am new to R so this is probably very obvious but the documentation is often somewhat terse.
This is easier to do if you convert your matrix to a data frame using as.data.frame(). In that case the previous answers (using subset or m$three) will work, otherwise they will not.
To perform the operation on a matrix, you can define a column by name:
m[m[, "three"] == 11,]
Or by number:
m[m[,3] == 11,]
Note that if only one row matches, the result is an integer vector, not a matrix.