[R] Extract entries from matrix

[Jorge I Velez]

Dear R-help,

I am working with a matrix "m" from which I would like to extract some
elements.  An toy example is as follows:

## input matrix
m <- structure(c(0L, 0L, 0L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 0L, 0L, 0L, 2L, 2L, 2L, 2L,
2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 0L,
0L, 0L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L,
3L, 3L, 3L, 3L, 3L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 4L, 4L, 4L,
4L, 4L, 4L, 4L, 4L, 4L, 4L, 4L, 4L, 4L, 4L, 0L, 0L, 0L, 0L, 0L,
0L, 0L, 0L, 0L, 0L, 5L, 5L, 5L, 5L, 5L, 5L, 5L, 5L, 5L, 5L, 5L,
5L), .Dim = c(22L, 5L))

R> m
#         [,1]  [,2] [,3] [,4] [,5]
#  [1,]    0    0    0    0    0
#  [2,]    0    0    0    0    0
#  [3,]    0    0    0    0    0
#  [4,]    1    2    3    0    0
#  [5,]    1    2    3    0    0
#  [6,]    1    2    3    0    0
#  [7,]    1    2    3    0    0
#  [8,]    1    2    3    0    0
#  [9,]    1    2    3    4    0
# [10,]   1    2    3    4    0
# [11,]   1    2    3    4    5
# [12,]   1    2    3    4    5

>From "m", I would like to extract the entries

4, 1
5, 2
6, 3
7, 1
8, 2
9, 3
10, 1
11, 2
12, 3

so at the end of applying a function "f" to "m" I get

1, 2, 3, 1, 2, 3, 4, 1, 2, 3


Basically the idea is to extract the diagonal elements until a zero is
found.

In the real problem the dimensions of "m" are much bigger, but this smaller
version of "m" illustrate what needs to be done.

I would greatly appreciate any ideas on how to do this.

Thanks in advance,
Jorge Velez.-

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