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Re: array problems [message #61295 is a reply to message #61294]

Fri, 11 July 2008 12:20

jschwab@gmail.com
Messages: 30
Registered: December 2006

Member

On Jul 11, 2:36 pm, "David Sheerin" <davidshee...@btinternet.com>
wrote:
> Hi All
> I have a palindromic vector of floats, e.g. [a,b,c,b,a] , and I would like
> to expand it to include the mean between each value like [(0+a)/2, a,
> (a+b)/2, b, (b+c)/2, c, (c+b)/2, b, (b+a)/2, a, (a+0)/2]. Is there any
> elegant way of doing this without having to resort to clunky for loops?
>
> I also would like to repeat this action on the resulting vector.
>
> Thanks for any tips
>
> David

You can do this in a few lines with a combination of rebin and shift.

;; Take only the first section of the array
half = [a, b, c]

;; use rebin with the sample keyword to duplicate your values
;; this gives [a, a, b, b, c, c]
n = n_elements(half)
doubled = rebin(half, 2 * n, /sample)

;; now use shift to combine and average, and drop the last element
extended = ((doubled + shift(doubled, -1)) / 2.0)[0:2*n-2]

;; now you can use reverse() and array concatenation to do back
;; to the full palindromic array

Josiah

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[Message index]

		Re: array problems By: pgrigis on Fri, 11 July 2008 12:59
		Re: array problems By: jschwab@gmail.com on Fri, 11 July 2008 12:26
		Re: array problems By: Jean H. on Fri, 11 July 2008 12:02
		Re: array problems By: jschwab@gmail.com on Fri, 11 July 2008 12:20
		Re: array problems By: Vince Hradil on Fri, 11 July 2008 12:03
		Re: array problems By: Bob[3] on Mon, 14 July 2008 08:16
		Re: array problems By: David Sheerin on Tue, 15 July 2008 12:24

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