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Re: How to extract a scalar from a vector? [message #74161 is a reply to message #74160]

Tue, 04 January 2011 15:43

penteado
Messages: 866
Registered: February 2018

Senior Member
Administrator

> I think the problem is that IDL thinks that cal_data[sel_cal_data,2]
> and cal_data[sel_cal_data,3] are vectors of dimension 1, when they
> should be scalars.

I do not know what you mean by "thinks they are" 1-element arrays.
They *are* 1-element arrays. Any time an array indexed by an array (in
this case, the result of where), the result is an array, even if it
only has 1 element.

> See this:
> IDL> help,cal_data[sel_cal_data,
> 3]
> <Expression> DOUBLE = Array[1]

You are right that this is the problem, since the product of arrays of
different sizes has the size of the smaller of the two, in this case,
1.

> How on earth can I make cal_data[sel_cal_data,2] and
> cal_data[sel_cal_data,3] into a scalar? I tried this:

Use just one element of sel_cal_data (the one element is a scalar),
instead of the whole sel_cal_data array:

cal_data[sel_cal_data[0],3]

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[Message index]

		Re: How to extract a scalar from a vector? By: Balt on Tue, 04 January 2011 16:03
		Re: How to extract a scalar from a vector? By: penteado on Tue, 04 January 2011 15:43
		Re: How to extract a scalar from a vector? By: David Fanning on Tue, 04 January 2011 15:37
		Re: How to extract a scalar from a vector? By: R.Bauer on Tue, 18 January 2011 23:07
		Re: How to extract a scalar from a vector? By: chrisbuc on Wed, 11 October 2017 03:10
		Re: How to extract a scalar from a vector? By: David Fanning on Tue, 04 January 2011 16:08

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