Cropping a matrix by rows

I am working with matrices that represent images.  I believe its
important
to create them as new objects because what I would like to export these
cropped images as new files. Sorry if I didn't include that if it as
important information.


On Sun, Nov 11, 2012 at 1:36 PM, Jeff Newmiller
<jdnewmil at dcn.davis.ca.us>wrote:

I assiduously avoid automatically generating distinct objects, and
recommend that you also do so.
You have the data, and can refer to individual rows by index as you

need

them.

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Hans Thompson <hans.thompson1 at gmail.com> wrote:

Hello r-help,

I've been banging my head against the computer in an attempt to

learn

how
to divide my matrix into segments by rows. I want to be able to

return

each
segment as a newly named object.  I've tried looking at the apply
functions
and creating a for loop but brain no work.  Here's the basic

starting

objects that I believe would be needed to separate the matrix.

mat <- matrix(c(1:40),10,4)
rowcropping <- sort(sample(2:9,2))
rowcropping <- c(1,rowcropping,length(mat[,1]))
mat[rowcropping[1]:rowcropping[2],]

I want something like the last line as the first object but getting
them
all by automation  as separate objects is my goal.  Thanks.

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