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Re: array subtraction [message #63339 is a reply to message #63338]

Wed, 05 November 2008 08:29

Wout De Nolf
Messages: 194
Registered: October 2008

Senior Member

On Wed, 5 Nov 2008 07:25:10 -0800 (PST), julia.walterspiel@gmail.com
wrote:

> hey guys
> SOS call from the newbie:
>
> I've got two data arrays, one of length 134 (=a), the other of length
> 75 (=b) with monthly cloud cover data from modis terra and aqua.
> Data from Terra starts feb 2000, data from Aqua starts july 2002.
>
> I want to calculate and plot the difference in cloud cover for each
> month from Terra and Aqua. so far so good.
>
> the two data arrays are "connected" by two (separate) time arrays c
> (for Terra, feb 2000 - now) and d (for Aqua july 2002 - now).
> that means, my data array "b" starts only somewhere at index so-and-so
> of "a" (not sure where exactly).
> Now, how can I tell IDL to subtract the two arrays at the right point,
> meaning subtract the terra-value on july 2002 from the aqua value on
> the same date?
>
> I'm sure everyone of you can do that with both eyes closed and it
> can't be difficult but I couldn't find any help online.
> thanks!
> juls

So you only need to get i in this:
diff = a[i:*]-b

In general I would say
i=value_locate(c,d[0])
but what format do the time/data arrays have (string, Julian Day
Number,...)?

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[Message index]

		Re: array subtraction By: Spon on Wed, 05 November 2008 08:39
		Re: array subtraction By: Wout De Nolf on Wed, 05 November 2008 08:29
		Re: array subtraction By: Brian Larsen on Wed, 05 November 2008 08:29
		Re: array subtraction By: julia.walterspiel on Wed, 05 November 2008 08:15
		Re: array subtraction By: R.Bauer on Wed, 05 November 2008 07:58
		Re: array subtraction By: julia.walterspiel on Mon, 10 November 2008 07:59

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