Re: N_ELEMENTS and WHERE: Scalar or Array ?

[wmc(at)bas.ac.uk]

rmlongfield@my-dejanews.com wrote:
>Hi All, 	I keep making the same mistake with N_ELEMENTS so I decided
>to write and ask if anyone has found a solution.  I use WHERE to find some
>zeroes in a data set which I want to exclude in further processing.  Problem
>is that sometimes they are all zeroes.	Using a simple :

>non_zero_xvalues = WHERE (subarray1  GT 0)
>IF(non_zero_array EQ -1) ...

>gets me into trouble because, when it is an array, I get an error. If I use
>N_ELEMENTS(non_zero_array) there is always at least one element, whether it
>is -1 or something else.  I don't like ignoring the 'something else' value
>just because it is the only one.  Is the answer another IF statement or some
>sort of error control?

The temporay solution to this is to use where(wurble,count)...

But since this has come up, & its one of my pet peeves: why cannot where
return a null array to indicate no-elements-match. And then array[null] would
match to nothing. This would allow one to say

  array[where(wurble)]='stoat'

instead of the ugly

  i=where(wurble,count)
  if (count gt 0) then array[i]='stoat'

I use Perl a lot, and the contrast is very striking there: perl handles null
values quite happily and it simplifies a lot of things.

While I'm here: would RSI please put a decent regexp package into IDL?

-W.

-- 
William M Connolley | wmc@bas.ac.uk | http://www.nbs.ac.uk/public/icd/wmc/
Climate Modeller, British Antarctic Survey | Disclaimer: I speak for myself