Re: [R] How to find series of small numbers in a big vector?

From: Jonne Zutt <j.zutt_at_tudelft.nl>
Date: Tue 30 Jan 2007 - 11:53:49 GMT

I suggest the following appraoch

This gives TRUE for all data within the search_range

        A1 = my_data > search_range[1] & my_data < search_range[2]

which() gives us the indices

        A2 = which(A1)

and diff() the gaps between those intervals

        A3 = diff(A2)

Hence, if A3 > search_length, we have enough consecutive numbers within the search range

Finally, this is what you wanted to know?

        A2[ which(A3 > search_length) ]

On Mon, 2007-01-29 at 17:49 -0800, Ed Holdgate wrote:
> Hello:
>
> I have a vector with 120,000 reals
> between 0.00000 and 0.9999
>
> They are not sorted but the vector index is the
> time-order of my measurements, and therefore
> cannot be lost.
>
> How do I use R to find the starting and ending
> index of ANY and ALL the "series" or "sequences"
> in that vector where ever there are 5 or more
> members in a row between 0.021 and 0.029 ?
>
> For example:
>
> search_range <- c (0.021, 0.029) # inclusive searching
> search_length <- 5 # find ALL series of 5 members within search_range
> my_data <- c(0.900, 0.900, 0.900, 0.900, 0.900,
> 0.900, 0.900, 0.900, 0.900, 0.900,
> 0.900, 0.028, 0.024, 0.027, 0.023,
> 0.022, 0.900, 0.900, 0.900, 0.900,
> 0.900, 0.900, 0.024, 0.029, 0.023,
> 0.025, 0.026, 0.900, 0.900, 0.900,
> 0.900, 0.900, 0.900, 0.900, 0.900,
> 0.900, 0.900, 0.900, 0.900, 0.022,
> 0.023, 0.025, 0.333, 0.027, 0.028,
> 0.900, 0.900, 0.900, 0.900, 0.900)
>
> I seek the R program to report:
> start_index of 12 and an end_index of 16
> -- and also --
> start_index of 23 and an end_index of 27
> because that is were there happens to be
> search_length numbers within my search_range.
>
> It should _not_ report the series at start_index 40
> because that 0.333 in there violates the search_range.
>
> I could brute-force hard-code an R program, but
> perhaps an expert can give me a tip for an
> easy, elegant existing function or a tactic
> to approach?
>
> Execution speed or algorithm performance is not,
> for me in this case, important. Rather, I
> seek an easy R solution to find the time windows
> (starting & ending indicies) where 5 or more
> small numbers in my search_range were measured
> all in a row.
>
> Advice welcome and many thanks in advance.
>
> Ed Holdgate
>
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R-help@stat.math.ethz.ch mailing list
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. Received on Tue Jan 30 22:59:25 2007

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