From ggrothend|eck @end|ng |rom gm@||@com  Fri Oct 11 16:46:41 2019
From: ggrothend|eck @end|ng |rom gm@||@com (Gabor Grothendieck)
Date: Fri, 11 Oct 2019 10:46:41 -0400
Subject: [Rd] New matrix function
In-Reply-To: <CAL0QV_OHN1+c2ZMO28v9gB1Y-0c+2zL57bDCgcZse13bZ8--eQ@mail.gmail.com>
References: <CAL0QV_OHN1+c2ZMO28v9gB1Y-0c+2zL57bDCgcZse13bZ8--eQ@mail.gmail.com>
Message-ID: <CAP01uRn5KxHwB3o+9E9f2b+i-jAzpvXn-D5eNitqn57-oWVTPw@mail.gmail.com>

Using the example in the link here are two one-liners:

  A <- c(2,3,4,1,2,3,4,1,1,2)
  x <- c(1,2)

  # 1 - zoo
  library(zoo)
  which( rollapply(A, length(x), identical, x, fill = FALSE, align = "left") )
  ## [1] 4 9

  # 2 - Base R using conversion to character
  gregexpr(paste(x, collapse = ""), paste(A, collapse = ""))[[1]]
  ## [1] 4 9
  ...snip ...

On Fri, Oct 11, 2019 at 3:45 AM Morgan Morgan <morgan.emailbox at gmail.com> wrote:
>
> Hi All,
>
> I was looking for a function to find a small matrix inside a larger matrix
> in R similar to the one described in the following link:
>
> https://www.mathworks.com/matlabcentral/answers/194708-index-a-small-matrix-in-a-larger-matrix
>
> I couldn't find anything.
>
> The above function can be seen as a "generalisation" of the "which"
> function as well as the function described in the following post:
>
> https://coolbutuseless.github.io/2018/04/03/finding-a-length-n-needle-in-a-haystack/
>
> Would be possible to add such a function to base R?
>
> I am happy to work with someone from the R core team (if you wish) and
> suggest an implementation in C.
>
> Thank you
> Best regards,
> Morgan
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel



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[Rd] New matrix function
Gabor Grothendieck