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Re: Q: Quantil calculation in IDL? [message #17524 is a reply to message #17379]

Fri, 15 October 1999 00:00

Pavel Romashkin
Messages: 166
Registered: April 1999

Senior Member

Am I missing something? Is 75%-quantils not just a value of the sorted array 3/4
of the way through?

IDL> a = bindgen(256,256)
IDL> b = sort(a)
IDL> c = n_elements(b)*3/4
IDL> print, (a[b])[c]
192

So, 3/4 of all elements in A are less than 192. Sure enough, in this example a
median is as easy to get by replacing 3/4 with 1/2, and it is equal to 128.

Cheers,
Pavel

Joerg Mosthaf wrote:

> Hi,
> I have been searching the help files and David Fannings great book, but I can't
> find a way to calculate 25%- and 75%-quantils. Unfortunately I don't know the
> english name for this so let me explain: A 75%-quantil is like the median, but
> with 75% instead of 50% i.e. the number in a data spread, that 75% of all
> data points are less or equal to. Is there a way to do this fast on an
> 256x256 array? I need it to cut off noise at a specific level and to get a
> reliable min/max value, not including data spikes. I am probably overlooking
> something very easy, but I just couldn't find it.
>
> Thanks,
> Joerg Mosthaf

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[Message index]

		Q: Quantil calculation in IDL? By: joerg.mosthaf on Fri, 15 October 1999 00:00
		Re: Q: Quantil calculation in IDL? By: m218003 on Mon, 25 October 1999 00:00
		Re: Q: Quantil calculation in IDL? By: James Tappin on Mon, 18 October 1999 00:00
		Re: Q: Quantil calculation in IDL? By: joerg.mosthaf on Mon, 18 October 1999 00:00
		Re: Q: Quantil calculation in IDL? By: J.D. Smith on Fri, 15 October 1999 00:00
		Re: Q: Quantil calculation in IDL? By: J.D. Smith on Fri, 15 October 1999 00:00
		Re: Q: Quantil calculation in IDL? By: Pavel Romashkin on Fri, 15 October 1999 00:00
		Re: Q: Quantil calculation in IDL? By: davidf on Fri, 15 October 1999 00:00

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