[R] Extract entries from matrix
Jorge I Velez
jorgeivanvelez at gmail.com
Wed Oct 28 18:17:54 CET 2015
Dear all,
I thought I would better send an image illustrating that the problem is
(hope the file gets through). In the picture, the matrix "m" is given by
## input
m <- structure(c(0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 2, 2,
2, 2, 2, 2, 2, 2, 2, 0, 0, 0, 3, 3, 3, 3, 3, 3, 3, 3, 3, 0, 0,
0, 0, 0, 0, 0, 0, 4, 4, 4, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 5,
5), .Dim = c(12L, 5L))
We start from the entry [1,1] and select all values in the diagonal until
we find the first zero. That is, we select the values in purple. Because
the first zero is found in [4,4], the next matrix begins in the 4th row.
The values of interest would be 1, 2, 3, 4, 5 (light blue). The last value
in this resulting vector is entry m[8,5], which is located at the maximum
number of columns of m. Hence, the next matrix to work with starts at row 9
and the values of interest are 1, 2 (in orange).
The output vector would then be of the same length as the number of rows in
"m", and would contain the elements previously selected.
Any ideas on how to proceed?
Thank you very much in advance.
Best regards,
Jorge Velez.-
On Tue, Oct 27, 2015 at 4:38 PM, Jorge I Velez <jorgeivanvelez at gmail.com>
wrote:
> Thank you all for your solutions and comments.
>
> As Dr. Carlson mentioned, we leave rows 1 to 3 out as they are all zeroes.
> Then, the entries I need to select from m are
>
> ----------------
> entry value
> ----------------
> 4,1 ---> 1
> 5,2 ---> 2
> 6,3 ---> 3
> 7,1 ---> 1
> 8,2 ---> 2
> 9,3 ---> 3
> 10,4 ---> 4
> 11,5 ---> 5
> 12,1 ---> 1
>
> Note that the entry [7,4] is zero, so we start from the first column in
> the 7th row and then select entry [7,1] instead. That's what I meant by "...
> the idea is to extract the diagonal elements until a zero is found." I
> should have said *entries* instead of _diagonal elements_. I am sorry Dr.
> Turner for the confusion.
>
> Starting with m
>
> 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
>
> the first submatrix to work with is
>
> # [4,] 1 2 3 0 0
> # [5,] 1 2 3 0 0
> # [6,] 1 2 3 0 0
>
> from which the elements of interest are 1, 2, 3. Note that the 7th row of
> m is not included here because m[7, 5] = 0.
>
> Further, the second submatrix is
>
> # [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
>
> and the corresponding elements are 1, 2, 3, 4, 5.
>
> And the last matrix is
>
> #[12,] 1 2 3 4 5
>
> from which the position [12,1] is selected.
>
> So, the resulting entries from this process are 1, 2, 3, 1, 2, 3, 4, 5, 1.
>
> Thank you in advance for any additional insight you may provide.
>
> Regards,
> Jorge Velez.-
>
>
>
> On Tue, Oct 27, 2015 at 4:06 PM, David L Carlson <dcarlson at tamu.edu>
> wrote:
>
>> I don't see how you are getting the result you provide.
>>
>> > 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
>> > t(sapply(1:8, function(x) diag(m[x:12, ])))
>> [,1] [,2] [,3] [,4] [,5]
>> [1,] 0 0 0 0 0
>> [2,] 0 0 3 0 0
>> [3,] 0 2 3 0 0
>> [4,] 1 2 3 0 0
>> [5,] 1 2 3 0 0
>> [6,] 1 2 3 4 0
>> [7,] 1 2 3 4 5
>> [8,] 1 2 3 4 5
>>
>> These are all of the diagonals from the 1st through 8th rows. The first 3
>> begin with 0 so we leave them out, but then we have 4th: 1, 2, 3; 5th: 1,
>> 2, 3; 6th: 1, 2, 3, 4, etc so you must have some additional rule in mind to
>> get your answer.
>>
>> -------------------------------------
>> David L Carlson
>> Department of Anthropology
>> Texas A&M University
>> College Station, TX 77840-4352
>>
>>
>>
>> -----Original Message-----
>> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Jorge I
>> Velez
>> Sent: Tuesday, October 27, 2015 2:44 PM
>> To: jim holtman
>> Cc: R-help
>> Subject: Re: [R] Extract entries from matrix
>>
>> Dear Jim,
>>
>> Thank you very much for your quick reply.
>>
>> I am sorry for the confusion it may have caused, but I messed up the
>> indexes in my example. I would like, from the following matrix "m"
>>
>> ## input
>> m <- structure(c(0L, 0L, 0L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 0L,
>> 0L, 0L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 0L, 0L, 0L, 3L, 3L,
>> 3L, 3L, 3L, 3L, 3L, 3L, 3L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 4L,
>> 4L, 4L, 4L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 5L, 5L), .Dim = c(12L,
>> 5L))
>>
>> to obtain
>>
>> 1 2 3 1 2 3 4 5 1
>>
>> Sure using m[idx] will give the desired result. The problem is that idx
>> is
>> not known and needs to be determined from "m". I would like to use
>> something like
>>
>> extractDiagonals(m)
>> ## [1] 1 2 3 1 2 3 4 5 1
>>
>> I look forward to your reply. Thanks in advance.
>>
>> Best regards,
>> Jorge Velez.-
>>
>>
>>
>> On Tue, Oct 27, 2015 at 2:31 PM, jim holtman <jholtman at gmail.com> wrote:
>>
>> > If you want to use the numbers you gave a the index into the matrix,
>> then
>> > you can create a matrix with the values and then index into 'm'. I
>> don't
>> > see a '4' in the output example you gave using your index values:
>> >
>> > > 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))
>> > > # create index matrix
>> > > indx <- matrix(c(4, 1,
>> > + 5, 2,
>> > + 6, 3,
>> > + 7, 1,
>> > + 8, 2,
>> > + 9, 3,
>> > + 10, 1,
>> > + 11, 2,
>> > + 12, 3), ncol = 2, byrow = TRUE)
>> > >
>> > >
>> > > 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
>> > [13,] 1 2 3 4 5
>> > [14,] 1 2 3 4 5
>> > [15,] 1 2 3 4 5
>> > [16,] 1 2 3 4 5
>> > [17,] 1 2 3 4 5
>> > [18,] 1 2 3 4 5
>> > [19,] 1 2 3 4 5
>> > [20,] 1 2 3 4 5
>> > [21,] 1 2 3 4 5
>> > [22,] 1 2 3 4 5
>> > > indx
>> > [,1] [,2]
>> > [1,] 4 1
>> > [2,] 5 2
>> > [3,] 6 3
>> > [4,] 7 1
>> > [5,] 8 2
>> > [6,] 9 3
>> > [7,] 10 1
>> > [8,] 11 2
>> > [9,] 12 3
>> > > m[indx]
>> > [1] 1 2 3 1 2 3 1 2 3
>> >
>> >
>> > Jim Holtman
>> > Data Munger Guru
>> >
>> > What is the problem that you are trying to solve?
>> > Tell me what you want to do, not how you want to do it.
>> >
>> > On Tue, Oct 27, 2015 at 2:43 PM, Jorge I Velez <
>> jorgeivanvelez at gmail.com>
>> > wrote:
>> >
>> >> 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.-
>> >>
>> >> [[alternative HTML version deleted]]
>> >>
>> >> ______________________________________________
>> >> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> >> https://stat.ethz.ch/mailman/listinfo/r-help
>> >> PLEASE do read the posting guide
>> >> http://www.R-project.org/posting-guide.html
>> >> and provide commented, minimal, self-contained, reproducible code.
>> >>
>> >
>> >
>>
>> [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
>
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