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Re: data comparison [message #44270 is a reply to message #44269]

Wed, 01 June 2005 20:08

Mark Hadfield
Messages: 783
Registered: May 1995

Senior Member

angela wrote:
> I am trying to extract specific values from an array, datax (string
> array[1,300]).
> When I type the command
>
> print,datax GE 100
>
> it works fine and it gives me the correct answer. But when I type
>
> print,datax GE x
>
> where x has been defined in the program earlier as 100 and is an
> integer array[1]
> the result is -1 which is wrong since there are values in this array
> that are greater or equal than 100.
> Does anyone have an idea what is going on?

You have been bitten by a common pitfall. The clue is that x is a
single-element array, not a scalar. The result of an arithmetic or
comparison operation between two arrays of different length is an array
with the shorter length, eg

IDL> help, fltarr(10)+fltarr(5)
<Expression> FLOAT = Array[5]

So when you do

IDL> print,datax GE x

you are comparing the first elements of datax with the first element of
x and discarding the rest. Try

IDL> print,datax GE x[0]

or

IDL> x = x[0]
IDL> print,datax GE x

--
Mark Hadfield "Ka puwaha te tai nei, Hoea tatou"
m.hadfield@niwa.co.nz
National Institute for Water and Atmospheric Research (NIWA)

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[Message index]

		Re: data comparison By: angela on Wed, 01 June 2005 20:33
		Re: data comparison By: Mark Hadfield on Wed, 01 June 2005 20:08
		Re: data comparison By: angela on Wed, 01 June 2005 19:25
		Re: data comparison By: Benjamin Hornberger on Wed, 01 June 2005 14:44

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