| help with - count in where() function [message #90868] |
Thu, 30 April 2015 10:32  |
g.nacarts
Messages: 148
Registered: November 2013
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Senior Member |
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Hi
I wrote a simple example of my code to understand the behaviour of count in the where() function but I still don't understand something.
My example:
array = [[-1,2,3,4,5],[6,-7,8,9,10]]
mask =bytarr(5,5)
for i=0L,4 do begin
for j=0L, 4 do begin
IF (TOTAL(ARRAY GT 5.)+ TOTAL(Array LT 0.)) EQ 0 THEN mask[i,j]=1
endfor
endfor
ind = where(mask EQ 1,count)
print, count
IDL> 0
print, total(array GT 5.)
> IDL 4.00000
print, total(array LT 0.)
> IDL 2.00000
I was expecting the answers in the two last prints. I don't understand why when I print out the count it's zero. Can anyone help?
Actually I was expecting to be 4 because there are 2 negatives and 4 greater than 5 so (2+4=6, thus 10-6=4).
Thanks
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| Re: help with - count in where() function [message #90869 is a reply to message #90868] |
Thu, 30 April 2015 10:58  |
Paul Van Delst[1]
Messages: 1157
Registered: April 2002
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Senior Member |
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On 04/30/15 13:32, g.nacarts@gmail.com wrote:
> Hi
>
> I wrote a simple example of my code to understand the behaviour of
count in the where() function but I still don't understand something.
>
> My example:
>
> array = [[-1,2,3,4,5],[6,-7,8,9,10]]
> mask =bytarr(5,5)
> for i=0L,4 do begin
> for j=0L, 4 do begin
> IF (TOTAL(ARRAY GT 5.)+ TOTAL(Array LT 0.)) EQ 0 THEN mask[i,j]=1
> endfor
> endfor
>
> ind = where(mask EQ 1,count)
> print, count
> IDL> 0
>
>
> print, total(array GT 5.)
>> IDL 4.00000
> print, total(array LT 0.)
>> IDL 2.00000
>
>
> I was expecting the answers in the two last prints. I don't
> understand
why when I print out the count it's zero. Can anyone help?
>
> Actually I was expecting to be 4 because there are 2 negatives and 4
greater than 5 so (2+4=6, thus 10-6=4).
Umm....but you're asking to set the mask element if 4+2 = 0.
Last time I checked, 4+2 never equals 0 (in this universe at least) so
no mask elements will ever be set to 1.
Maybe your TOTAL() commands require some additional info re the i or j
indices?
Or am I being brain dead here?
cheers,
paulv
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| Re: help with - count in where() function [message #90872 is a reply to message #90868] |
Fri, 01 May 2015 07:33 |
Phillip Bitzer
Messages: 223
Registered: June 2006
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Senior Member |
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On Thursday, April 30, 2015 at 12:32:32 PM UTC-5, g.na...@gmail.com wrote:
> Hi
>
> I wrote a simple example of my code to understand the behaviour of count in the where() function but I still don't understand something.
>
> My example:
>
> array = [[-1,2,3,4,5],[6,-7,8,9,10]]
> mask =bytarr(5,5)
> for i=0L,4 do begin
> for j=0L, 4 do begin
> IF (TOTAL(ARRAY GT 5.)+ TOTAL(Array LT 0.)) EQ 0 THEN mask[i,j]=1
> endfor
> endfor
>
> ind = where(mask EQ 1,count)
>
> I was expecting the answers in the two last prints. I don't understand why when I print out the count it's zero.
Why do expect that to be the answer? Look at your loop again:
> for i=0L,4 do begin
> for j=0L, 4 do begin
> IF (TOTAL(ARRAY GT 5.)+ TOTAL(Array LT 0.)) EQ 0 THEN mask[i,j]=1
> endfor
> endfor
When, i=0, j=0, the total of `array GT 5` is 4 and the total of `array LT 0` is two.
When i=0, j=1, the total of `array GT 5` is 4 and the total of `array LT 0` is two.
When i=0, j=2, the total of `array GT 5` is 4 and the total of `array LT 0` is two.
See a pattern? ;-)
So, TOTAL(ARRAY GT 5.)+ TOTAL(Array LT 0.)) is never 0, as PaulV said.
Now, what exactly is the problem you're trying to solve?
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