comp.lang.idl-pvwave archive: archive » How to find second minimum elements in an array in IDL?

Home » Public Forums » archive » How to find second minimum elements in an array in IDL?

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: How to find second minimum elements in an array in IDL? [message #64813 is a reply to message #64677]

Fri, 16 January 2009 07:48

pgrigis
Messages: 436
Registered: September 2007

Senior Member

cmanc...@gmail.com wrote:
> On Jan 15, 5:39 pm, "mgal...@gmail.com" <mgal...@gmail.com> wrote:
>> On Jan 15, 10:36 am, cmanc...@gmail.com wrote:
>>
>>
>>
>>> I was curious, so I checked out your routine Mike. It looks good but
>>> one problem - a for loop! I'm pretty sure you can replace:
>>
>>> nCandidates = 0L
>>> for bin = 0L, nBins - 1L do begin
>>> nCandidates += h[bin]
>>> if (nCandidates ge n) then break
>>> endfor
>>
>>> with:
>>
>>> max( total( h, /cumulative ) < n, bin )
>>
>>> which should work because max will return the first maximum value. Of
>>> course, I was too lazy to see if the max(total()) method is actually
>>> faster (since it involves a couple different compuatations), but oh
>>> well, sometimes laziness wins :)
>>
>> It turns out that it probably doesn't matter much.
>>
>> It's not FOR loops per se that are bad, but the execution of many
>> statements. For perfectly uniformly distributed data, the FOR loop
>> above will only loop once -- more times the less uniformly distributed
>> the data, bounded by the number of bins (i.e. number of data
>> elements / number of elements required).
>>
>> Averages were computed for 500 runs of finding the smallest k=100
>> elements of an n=1000000 element dataset.
>>
>> For uniform data:
>>
>> mg_n_smallest(randomu(seed, n), k)
>>
>> vectorized: 0.035663 seconds
>> loops: 0.036040 seconds
>> loops are 1.1% faster
>>
>> For perverse data:
>>
>> mg_n_smallest([randomu(seed, k - 1), randomu(seed, n - k + 1) + n /
>> k], 100)
>>
>> vectorized: 0.279783 seconds
>> loops: 0.281627 seconds
>> vectorized is 0.7% faster
>>
>> Mike
>> --www.michaelgalloy.com
>> Tech-X Corporation
>> Associate Research Scientist
>
> I didn't really expect much of a difference. I think this is just a
> personal preference of mine - it looks so much nice when it all fits
> on one line!

But we don't want to encourage people writing
all of their programs in one line, don't we?

Ciao,
Paolo

Report message to a moderator

[Message index]

		How to find second minimum elements in an array in IDL? By: Hu on Wed, 14 January 2009 07:26
		Re: How to find second minimum elements in an array in IDL? By: Michael Galloy on Thu, 15 January 2009 14:39
		Re: How to find second minimum elements in an array in IDL? By: Conor on Fri, 16 January 2009 07:08
		Re: How to find second minimum elements in an array in IDL? By: Conor on Thu, 15 January 2009 09:36
		Re: How to find second minimum elements in an array in IDL? By: Michael Galloy on Wed, 14 January 2009 07:53
		Re: How to find second minimum elements in an array in IDL? By: Hu on Wed, 14 January 2009 07:45
		Re: How to find second minimum elements in an array in IDL? By: pgrigis on Fri, 16 January 2009 07:48

Previous Topic:	Re: Two Million Visitors!
Next Topic:	Question relating to IDL wavelet methods

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Fri Oct 10 08:23:24 PDT 2025

Total time taken to generate the page: 0.96200 seconds