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Re: The IDL way: Find last non-zero value [message #67729 is a reply to message #67728]

Mon, 24 August 2009 17:12

Jeremy Bailin
Messages: 618
Registered: April 2008

Senior Member

On Aug 24, 4:42 pm, Eric Hudson <ehud...@mit.edu> wrote:
> Thanks to all of you for the suggestions. I timed them all on several
> of the larger matrices and found that the last suggestion (using
> cumulative totals) was about twice as fast as the previous ones, and
> about 5 times faster than the brute force loop. It did depend on how
> many zeros ended each line on average. When the number was small the
> loop could win, but for my typical matrices the cumulative total is
> the clear winner.
>
> Thanks again,
> Eric

I'm shocked that no one's suggested histogram! Here's my take, which
I'd wager does at least as well as the cumulative totals:

sz=size(array,/dimen)
ncol=sz[0]
nrow=sz[1]
evenrows = 2*lindgen(nrow)
h = histogram( (array ne 0) + rebin(reform(evenrows,
1,nrow),ncol,nrow), min=0, max=2*nrow-1, $
reverse_indices=ri)
result = ri[ri[evenrows+2]-1] mod ncol
w = where(h[evenrows+1] eq 0, nw)
if nw gt 0 then result[evenrows[w]]=-1

-Jeremy.

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[Message index]

		Re: The IDL way: Find last non-zero value By: Jeremy Bailin on Mon, 24 August 2009 19:53
		Re: The IDL way: Find last non-zero value By: Jeremy Bailin on Mon, 24 August 2009 19:43
		Re: The IDL way: Find last non-zero value By: penteado on Mon, 24 August 2009 18:35
		Re: The IDL way: Find last non-zero value By: Jeremy Bailin on Mon, 24 August 2009 17:12
		Re: The IDL way: Find last non-zero value By: Eric Hudson on Mon, 24 August 2009 13:42
		Re: The IDL way: Find last non-zero value By: cgguido on Sun, 23 August 2009 20:39
		Re: The IDL way: Find last non-zero value By: penteado on Sun, 23 August 2009 19:10
		Re: The IDL way: Find last non-zero value By: Chris[6] on Sun, 23 August 2009 17:32

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