I have the following matrix:
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,] 0 0 0 0 0 0 0 0 0 0
[2,] 0 0 0 0 0 0 0 0 0 0
[3,] 0 0 0 0 0 0 0 0 0 0
[4,] 1 1 1 1 0 0 0 0 0 0
[5,] 1 1 1 1 0 0 0 0 0 0
[6,] 1 1 1 1 0 0 0 0 0 0
[7,] 1 1 1 1 0 0 0 0 0 0
[8,] 1 1 1 1 0 0 0 0 0 0
[9,] 1 1 1 1 0 0 0 0 0 0
[10,] 1 1 1 1 0 0 0 0 0 0
and I would like to know how to extract the 7x4 dimension of the submatrix with elements equal to 1.
Similar to JDLs answer, but giving you the sub matrix dimensions directly:
mat <- structure(c(
0L, 0L, 0L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
0L, 0L, 0L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
0L, 0L, 0L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
0L, 0L, 0L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L,
0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L,
0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L,
0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L,
0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L,
0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L
), .Dim = c(10L, 10L), .Dimnames = list(NULL, NULL))
dim(mat[apply(mat, 1, any), apply(mat, 2, any)])
#[1] 7 4
This will remove rows and columns containing only zeros. If you want to keep rows and columns containing at least one 1, you could do:
mat[3, 5] <- 2 #just to complicate it a little
f <- function(x) any(x==1) #create a simple function
dim(mat[apply(mat, 1, f), apply(mat, 2, f)])
#[1] 7 4