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what is the highest subscript in the array?!? [message #70774]

Thu, 06 May 2010 19:12

munka
Messages: 36
Registered: December 2009

Member

Hello team,

I find myself wanting to use the highest subscript in an array and
coding "flux[n_elements(flux)-1]"... I seem to remember seeing a
shortcut on here, and I can't remember what it is.

It's irrelevant, but here is where I most recently used this. This
finds the local maximum in an array.
index=where(flux eq max(flux) and flux ne flux[0] and flux ne
flux[n_elements(flux)-1],ct)

Thanks in advance,

~Bill

PS: Right before I posted this, I searched and I figured that
array[[-1]] should return the highest array value... but it doesn't,
and I'm still stumped.

IDL> array=indgen(10)
IDL> print,array[0]
0
IDL> print,array[9]
9
IDL> print,array[10]
% Attempt to subscript ARRAY with <INT ( 10)> is out of
range.
% Execution halted at: $MAIN$
IDL> print,array[[10]]
9
IDL> print,array[[-1]]
0
IDL> print,array[[-2]]
0
IDL>

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Re: what is the highest subscript in the array?!? [message #70847 is a reply to message #70774]

Fri, 07 May 2010 19:09

munka
Messages: 36
Registered: December 2009

Member

On May 7, 2:05 pm, pp <pp.pente...@gmail.com> wrote:
>
> Could do something like
>
> nflux=n_elements(flux)
> local_maxima=where((flux[1:nflux-2] ge flux[2:nflux-1]) and
> (flux[1:nflux-2] ge flux[0:nflux-3]))+1
>
> That would give the indexes of all points that are local maxima,
> defined as those larger than or equal to their immediate neighbors.
> Then max() or histogram() may be used to pick the highest maxima,
> depending on what is wanted.

Oh yeah! Is there an easy way to increase the "window" range from
just the points next to the point in question to some larger range?

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Re: what is the highest subscript in the array?!? [message #70849 is a reply to message #70774]

Fri, 07 May 2010 12:05

penteado
Messages: 866
Registered: February 2018

Senior Member
Administrator

On May 7, 3:46 pm, munka <mynameismu...@gmail.com> wrote:
>> On May 7, 6:20 am, wlandsman <wlands...@gmail.com> wrote:
>> Sorry, that should be
>
>> dum = max(flux[1:N_elements(flux)-2], c) & index = c+1
>
> That still does not return the LOCAL maximum. If the max is on the
> edge, it will still return a value
>
> IDL> flux=findgen(10)
> IDL> print,flux
> 0.00000 1.00000 2.00000 3.00000 4.00000
> 5.00000
> 6.00000 7.00000 8.00000 9.00000
> IDL> print,max(flux)
> 9.00000
> IDL> print,max(flux[1:N_elements(flux)-2], c)
> 8.00000
> IDL> print,c+1
> 8

Could do something like

nflux=n_elements(flux)
local_maxima=where((flux[1:nflux-2] ge flux[2:nflux-1]) and
(flux[1:nflux-2] ge flux[0:nflux-3]))+1

That would give the indexes of all points that are local maxima,
defined as those larger than or equal to their immediate neighbors.
Then max() or histogram() may be used to pick the highest maxima,
depending on what is wanted.

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Re: what is the highest subscript in the array?!? [message #70850 is a reply to message #70774]

Fri, 07 May 2010 11:51

munka
Messages: 36
Registered: December 2009

Member

On May 7, 10:37 am, eddie <eha...@gmail.com> wrote:
>> PS: Right before I posted this, I searched and I figured that
>> array[[-1]] should return the highest array value... but it doesn't,
>> and I'm still stumped.
>
> Add a 'u' and it should. A negative unsigned number "wraps" to
> produce a large number.
>
> IDL> array = indgen(10)
> IDL> print,array[[-1u]]
> 9
> This is similar to Carsten's huge number as an index. You can use
> array[[-1ull]] if you are concerned that your array might have more
> than a gajillion elements.
>
> Unfortunately this trick only works for the last element, array[[-2u]]
> still returns the last element of the array, not the second to last.
>
> Cheers,
> eddie

IDL> flux=findgen(10)
IDL> print,flux
0.00000 1.00000 2.00000 3.00000 4.00000
5.00000
6.00000 7.00000 8.00000 9.00000
IDL> print,flux[[-1u]]
9.00000
IDL> print,flux[5:*]
5.00000 6.00000 7.00000 8.00000 9.00000

Yes! The -1u works! I think I remembered the "trick" that I was
originally thinking of. It doesn't do what I want it to do, but the
[[-1u]] works!

Thanks for the responses!
~Bill

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Re: what is the highest subscript in the array?!? [message #70851 is a reply to message #70774]

Fri, 07 May 2010 11:46

munka
Messages: 36
Registered: December 2009

Member

> On May 7, 6:20 am, wlandsman <wlands...@gmail.com> wrote:
> Sorry, that should be
>
> dum = max(flux[1:N_elements(flux)-2], c) & index = c+1

That still does not return the LOCAL maximum. If the max is on the
edge, it will still return a value

IDL> flux=findgen(10)
IDL> print,flux
0.00000 1.00000 2.00000 3.00000 4.00000
5.00000
6.00000 7.00000 8.00000 9.00000
IDL> print,max(flux)
9.00000
IDL> print,max(flux[1:N_elements(flux)-2], c)
8.00000
IDL> print,c+1
8

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Re: what is the highest subscript in the array?!? [message #70852 is a reply to message #70774]

Fri, 07 May 2010 08:37

eddie
Messages: 1
Registered: May 2010

Junior Member

> PS: Right before I posted this, I searched and I figured that
> array[[-1]] should return the highest array value... but it doesn't,
> and I'm still stumped.

Add a 'u' and it should. A negative unsigned number "wraps" to
produce a large number.

IDL> array = indgen(10)
IDL> print,array[[-1u]]
9
This is similar to Carsten's huge number as an index. You can use
array[[-1ull]] if you are concerned that your array might have more
than a gajillion elements.

Unfortunately this trick only works for the last element, array[[-2u]]
still returns the last element of the array, not the second to last.

Cheers,
eddie

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Re: what is the highest subscript in the array?!? [message #70859 is a reply to message #70774]

Fri, 07 May 2010 03:35

wlandsman
Messages: 743
Registered: June 2000

Senior Member

On May 7, 6:20 am, wlandsman <wlands...@gmail.com> wrote:

>
> Not relevant to your main question, but if you care about speed and
> have more than 2 elements than it is faster to write (not tested)
>
> dum = max(flux[1:N_elements(flux)-1], c) & index = c+1
>

Sorry, that should be

dum = max(flux[1:N_elements(flux)-2], c) & index = c+1

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Re: what is the highest subscript in the array?!? [message #70860 is a reply to message #70774]

Fri, 07 May 2010 03:20

wlandsman
Messages: 743
Registered: June 2000

Senior Member

On May 6, 10:12 pm, munka <mynameismu...@gmail.com> wrote:

> It's irrelevant, but here is where I most recently used this. This
> finds the local maximum in an array.
> index=where(flux eq max(flux) and flux ne flux[0] and flux ne
> flux[n_elements(flux)-1],ct)
>

Not relevant to your main question, but if you care about speed and
have more than 2 elements than it is faster to write (not tested)

dum = max(flux[1:N_elements(flux)-1], c) & index = c+1

--Wayne

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Re: what is the highest subscript in the array?!? [message #70861 is a reply to message #70774]

Fri, 07 May 2010 02:34

Carsten Lechte
Messages: 124
Registered: August 2006

Senior Member

munka wrote:
> IDL> array=indgen(10)
[...]
> IDL> print,array[[10]]
> 9

Well, your could use lasti = [9223372036854775807LL] to define an "index"
that will give you the last array element in most cases.
(Until someone sets COMPILE_OPT STRICTARRSUBS, at least)

IDL> print, array[lasti]
9

And possibly, God kills a kitten everytime someone uses this abomination.

chl

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Re: what is the highest subscript in the array?!? [message #70865 is a reply to message #70774]

Thu, 06 May 2010 22:39

R.G.Stockwell
Messages: 163
Registered: October 2004

Senior Member

"Michael Galloy" <mgalloy@gmail.com> wrote in message
news:hs0518$97o$1@speranza.aioe.org...
> On 5/6/10 8:44 pm, munka wrote:
>
> [snipped]
>
>> Also, clicking on your signature link brings me to "http://
>> www.google.com/www.michaelgalloy.com" :\
>
> Not sure what Google is doing there; it works fine in my newsreader, but
> Google Groups is doing something funky.

that may just be the default action for the poster's browser setup
(i.e. to send a linked string from another program into google).

i assure you: www.google.com/www.michaelgalloy.com does not exist.

Google
Error
Not Found
The requested URL /www.michaelgalloy.com was not found on this server.

I actually get that sometime (strangely enough) if I click a link that
is not found (wireless network lost or whatever), where the secondary
action is to try to fire the string off to a google search.

cheers,
bob

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Re: what is the highest subscript in the array?!? [message #77950 is a reply to message #70774]

Sat, 15 October 2011 11:57

Giuseppe Papa
Messages: 27
Registered: February 2010

Junior Member

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