| Re: N_ELEMENTS gt 0 [message #58758 is a reply to message #58676] |
Thu, 14 February 2008 10:12  |
Jean H.
Messages: 472
Registered: July 2006
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Senior Member |
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chloesharrocks@gmail.com wrote:
> Is it possible to combine the N_ELEMENTS function with the greater
> than operator? I just want to search through an array and find out
> how many elements exist which are greater than zero (I don't need to
> know where they are, just how many), but I can't get it to work. I
> have an array called good_index which I happen to know has 6 values >
> zero, but when I run the following code, it tells me I only have 1
> value > zero:
>
> number = (N_ELEMENTS(good_index) gt 0)
> print, number
>
> Is there a way to do this without using a where function?
> Thanks
> Chlo�
What you get is normal. N_elements(X) always returns 1 value, the number
of elements of X... so your statements returns 1 if good_index has at
least one element, and 0 if it is undefined.
Now, the easiest way is:
useless = where(good_index gt 0, countPositiveEntries)
useless = 0
print, countPositiveEntries
if you don't want that, you can use "total"
countPositiveEntries = total(good_index gt 0)
Note that you may have to use data[good_index]... it makes more sense,
as anyway you can't really have negative index (technically, you can,
but they make no sense!).
Jean
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