[R] Cropping a matrix by rows

[Jeff Newmiller]

Seems irrelevant to me. You can export the data to separate files directly from the matrix using matrix indexing. i.e.

for (i in 1:2) {
  write.table( mat[rowcropping[2*i-1]:rowcropping[2*i],],paste0("file",i,".dat")
}

Please use reply to all to keep the discussion on the list.
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Sent from my phone. Please excuse my brevity.

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

>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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>> Jeff Newmiller                        The     .....       .....  Go
>Live...
>> DCN:<jdnewmil at dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live
>> Go...
>>                                       Live:   OO#.. Dead: OO#.. 
>Playing
>> Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
>> /Software/Embedded Controllers)               .OO#.       .OO#. 
>rocks...1k
>>
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>> Sent from my phone. Please excuse my brevity.
>>
>> 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.
>> >
>> >       [[alternative HTML version deleted]]
>> >
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>>
>>