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| Re: REFORM: new subscripts must not change the number elements in array [message #90414 is a reply to message #90413] |
Mon, 02 March 2015 07:26   |
Moritz Fischer
Messages: 32
Registered: June 2013
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Member |
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Am 02.03.2015 um 16:19 schrieb g.nacarts@gmail.com:
> I have a 2D array of A=[200,200]
>
> I am running REFORM but get the following error
> "REFORM: New subscripts must not change the number elements in A"
>
> This is what I am doing
> A = reform(A, 100L, 200L*200L, /overwrite)
>
> Why isn't it working?
>
You are trying to reform an 40,000 element array to an array with
100*200*200 = 4,000,000 elements.
You could for example do
A = reform(A, 100L, 400L, /overwrite)
as 200*200 = 100*400
REFORM just changes the way IDL looks at an array.
To interpolate/blow up your array look at rebin!
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| Re: REFORM: new subscripts must not change the number elements in array [message #90415 is a reply to message #90413] |
Mon, 02 March 2015 07:31 |
Helder Marchetto
Messages: 520
Registered: November 2011
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Senior Member |
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On Monday, March 2, 2015 at 4:19:32 PM UTC+1, g.na...@gmail.com wrote:
> I have a 2D array of A=[200,200]
>
> I am running REFORM but get the following error
> "REFORM: New subscripts must not change the number elements in A"
>
> This is what I am doing
> A = reform(A, 100L, 200L*200L, /overwrite)
>
> Why isn't it working?
Because 4000 is not 4000000.
Let me show:
IDL> A=randomu(s,200,200)
IDL> print, product(size(a, /dimensions), /preserve_type)
40000
IDL> print, product([100L, 200L*200L], /preserve_type)
4000000
If your array is has 200 x 200 elements, the total is 40000.
Now with reform you want to make it 100 x (200x200)... this is 4000000.
Maybe (maybe!) what you want is:
a = reform(a, 100l, 200l*2l, /overwrite)
Cheers,
Helder
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| Re: REFORM: new subscripts must not change the number elements in array [message #90418 is a reply to message #90413] |
Mon, 02 March 2015 07:49 |
Matthew Argall
Messages: 286
Registered: October 2011
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Senior Member |
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Another possibility is that you want to reform your array to be 400x1, then copy it 100 times, so that you have a 100x400. In this case, you want
IDL> A = randomu(s, 200, 200)
IDL> A = rebin(reform(A, 1, 400), 100, 400)
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| Re: REFORM: new subscripts must not change the number elements in array [message #90422 is a reply to message #90421] |
Mon, 02 March 2015 08:19 |
Helder Marchetto
Messages: 520
Registered: November 2011
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Senior Member |
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On Monday, March 2, 2015 at 5:14:59 PM UTC+1, g.na...@gmail.com wrote:
>> What do you get if you type:
>> print, size(a)
>> before the reform command?
>>
>> Helder
>
> I got
>
> 2 200 200 4 40000
I don't see how you can get an error with the reform() command:
IDL> a = randomu(s, 200,200)
IDL> print, size(a)
2 200 200 4 40000
IDL> help, reform(a, 100l, 200l*2l)
<Expression> FLOAT = Array[100, 400]
Cheers,
Helder
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| Re: REFORM: new subscripts must not change the number elements in array [message #90423 is a reply to message #90416] |
Mon, 02 March 2015 08:24 |
Helder Marchetto
Messages: 520
Registered: November 2011
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Senior Member |
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On Monday, March 2, 2015 at 4:43:17 PM UTC+1, g.na...@gmail.com wrote:
> There is one thing I don't understand. Both of you suggest the same thing:
> a = reform(a, 100l, 200l*2l, /overwrite)
> You typed 200l*2l this is because we want 200x200 that's why you multiplied it by 2?
> What I want it's 100 x (200x200). So 100 2D images of dimensions [200,200]
Ok, so before, I didn't see this message.
You're sort of changing things around here.
You started from ONE array with 200x200 elements and wanted to make something of 100x(40000) elements. This of course will never work.
What you really want is to make a 100x200x200 array from 100 arrays of 200x200. Correct?
But where do you get the 100 arrays of 200x200?
Try this:
finalArray = fltarr(100,200,200)
for i=0, 99 do begin
;generate the array
a = randomu(s,200,200)
;put it in the final array
finalArray[i,0,0] = reform(a,1,200,200)
endfor
Regards,
Helder
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| Re: REFORM: new subscripts must not change the number elements in array [message #90424 is a reply to message #90423] |
Mon, 02 March 2015 08:46 |
g.nacarts
Messages: 148
Registered: November 2013
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Senior Member |
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I didn't understand the logic of this reform(a, 100l, 200l*2l).
If instead of A=[200,200] we have A=[216,216] and we want 120x(216x216) then this is written as reform(a, 120l, 216l*2l). Is that correct?
I am trying to understand how you end up with reform(a, 100l, 200l*2l). Because when I typed this
a = randomu(s, 216,216)
help, reform(a, 120l, 216l*2l,/overwrite)
I got the same error "REFORM: New subscripts must not change the number elements in A."
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| Re: REFORM: new subscripts must not change the number elements in array [message #90425 is a reply to message #90424] |
Mon, 02 March 2015 09:01 |
Helder Marchetto
Messages: 520
Registered: November 2011
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Senior Member |
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On Monday, March 2, 2015 at 5:46:52 PM UTC+1, g.na...@gmail.com wrote:
> I didn't understand the logic of this reform(a, 100l, 200l*2l).
> If instead of A=[200,200] we have A=[216,216] and we want 120x(216x216) then this is written as reform(a, 120l, 216l*2l). Is that correct?
>
> I am trying to understand how you end up with reform(a, 100l, 200l*2l). Because when I typed this
> a = randomu(s, 216,216)
> help, reform(a, 120l, 216l*2l,/overwrite)
> I got the same error "REFORM: New subscripts must not change the number elements in A."
Look, it's getting difficult to help if the cards keep on changing.
Did you see my last message? You can do the same thing without using reform(), because I think you have not read the documentation of the reform command.
xSize = 216
ySize = 216
nImages = 120
finalArray = fltarr(xSize,ySize,nImages)
for i=0, nImages-1 do begin
;generate the array
a = randomu(s,xSize,ySize)
;put it in the final array
finalArray[0,0,i] = a
endfor
I didn't use the reform. For your information this:
finalArray[0,0,i] = a
is the same as this:
finalArray[*,*,i] = a
Just a bit faster.
As an example, try this:
test = fltarr(3,3,5)
print, test
ones = fltarr(3,3)+1.0
test[0,0,2] = ones
print, test
Test contains 5 "images" of 3x3 pixels. When you first print it, you will see 5 images with zeros in each pixel. After
test[0,0,2] = ones
you will find that the third image is filled with ones.
I think this is described here:
http://www.exelisvis.com/docs/Array_Subscript_Ranges.html
in the section "Avoid using range subscripts for assignment".
Cheers,
Helder
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| Re: REFORM: new subscripts must not change the number elements in array [message #90427 is a reply to message #90413] |
Mon, 02 March 2015 09:12 |
g.nacarts
Messages: 148
Registered: November 2013
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Senior Member |
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Yes, I saw your last message but I am interested to understand how you end up before with the a = reform(a, 100l, 200l*2l, /overwrite). I followed your steps but I changed the dimensions to see if I understand well.
A=randomu(s,216,216)
IDL> print, product(size(a, /dimensions), /preserve_type)
46656
IDL> print, product([120L, 216L*216L], /preserve_type)
5598720
Then I tried to write it like this: a = reform(a, 120l, 216l*2l, /overwrite) but I got the error that I mentioned before.
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| Re: REFORM: new subscripts must not change the number elements in array [message #90428 is a reply to message #90424] |
Mon, 02 March 2015 09:20 |
Paul Van Delst[1]
Messages: 1157
Registered: April 2002
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Senior Member |
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On 03/02/15 11:46, g.nacarts@gmail.com wrote:
> I didn't understand the logic of this reform(a, 100l, 200l*2l). If
> instead of A=[200,200] we have A=[216,216] and we want 120x(216x216)
> then this is written as reform(a, 120l, 216l*2l). Is that correct?
No. That is not correct.
Read:
http://www.exelisvis.com/docs/REFORM.html
The very first line of the description (actually, the only line) says:
<quote>
The REFORM function changes the dimensions of an array without changing
the total number of elements.
</quote>
If you start with A=[200,200] and you want B=[200,200,100] (i.e. 100
sets of 200x200 arrays) then REFORM is not the command to use.
I think you want REBIN:
http://www.exelisvis.com/docs/REBIN.html
IDL> a=lindgen(4,4)
IDL> print, a
0 1 2 3
4 5 6 7
8 9 10 11
12 13 14 15
Now create 10 "copies" of a, stacked into a 3-D array:
IDL> b=rebin(a,4,4,10)
IDL> print, b[*,*,0]
0 1 2 3
4 5 6 7
8 9 10 11
12 13 14 15
IDL> print, b[*,*,6]
0 1 2 3
4 5 6 7
8 9 10 11
12 13 14 15
>
> I am trying to understand how you end up with reform(a, 100l,
> 200l*2l). Because when I typed this a = randomu(s, 216,216) help,
> reform(a, 120l, 216l*2l,/overwrite) I got the same error "REFORM: New
> subscripts must not change the number elements in A."
>
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| Re: REFORM: new subscripts must not change the number elements in array [message #90429 is a reply to message #90428] |
Mon, 02 March 2015 09:25 |
Paul Van Delst[1]
Messages: 1157
Registered: April 2002
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Senior Member |
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With apologies for replying to my own reply, but if you really want an
array B=[100,200,200] from a starting A=[200,200] array, you just use
TRANSPOSE (http://www.exelisvis.com/docs/TRANSPOSE.html) on the result
from REBIN:
IDL> help, b
B LONG = Array[4, 4, 10]
IDL> b = transpose(b,[2,0,1])
IDL> help, b
B LONG = Array[10, 4, 4]
IDL> print, b[0,*,*]
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
IDL> print, b[6,*,*]
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
On 03/02/15 12:20, Paul van Delst wrote:
> On 03/02/15 11:46, g.nacarts@gmail.com wrote:
>> I didn't understand the logic of this reform(a, 100l, 200l*2l). If
>> instead of A=[200,200] we have A=[216,216] and we want 120x(216x216)
>> then this is written as reform(a, 120l, 216l*2l). Is that correct?
>
> No. That is not correct.
>
> Read:
> http://www.exelisvis.com/docs/REFORM.html
>
> The very first line of the description (actually, the only line) says:
> <quote>
> The REFORM function changes the dimensions of an array without changing
> the total number of elements.
> </quote>
>
> If you start with A=[200,200] and you want B=[200,200,100] (i.e. 100
> sets of 200x200 arrays) then REFORM is not the command to use.
>
> I think you want REBIN:
> http://www.exelisvis.com/docs/REBIN.html
>
> IDL> a=lindgen(4,4)
> IDL> print, a
> 0 1 2 3
> 4 5 6 7
> 8 9 10 11
> 12 13 14 15
>
> Now create 10 "copies" of a, stacked into a 3-D array:
>
> IDL> b=rebin(a,4,4,10)
>
> IDL> print, b[*,*,0]
> 0 1 2 3
> 4 5 6 7
> 8 9 10 11
> 12 13 14 15
> IDL> print, b[*,*,6]
> 0 1 2 3
> 4 5 6 7
> 8 9 10 11
> 12 13 14 15
>
>>
>> I am trying to understand how you end up with reform(a, 100l,
>> 200l*2l). Because when I typed this a = randomu(s, 216,216) help,
>> reform(a, 120l, 216l*2l,/overwrite) I got the same error "REFORM: New
>> subscripts must not change the number elements in A."
>>
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| Re: REFORM: new subscripts must not change the number elements in array [message #90432 is a reply to message #90431] |
Mon, 02 March 2015 11:34 |
Phillip Bitzer
Messages: 223
Registered: June 2006
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Senior Member |
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On Monday, March 2, 2015 at 11:31:56 AM UTC-6, g.na...@gmail.com wrote:
> I read the documentation, and I noticed that The REFORM function changes the dimensions of an array without changing the total number of elements. That's what I want but I didn't understand how the others end up with a = reform(a, 100l, 200l*2l, /overwrite).
>
Then you really need to read it again.
Your original question asks why an array that is 200x200 can not be reformed into an array that 100x40000.
On Monday, March 2, 2015 at 1:25:24 PM UTC-6, g.na...@gmail.com wrote:
> I used the example provided by mo who said that 200*200=100*400. When a 2D array has dimensions [216,216] then 216*216=120*388.8
>
> when I tried a=reform(a,120l,388.8L,/overwrite) I got the old error
Uh, a dimension with 388.8 elements?
As someone was said around here before he "retired," no, no, you're doing it all wrong.
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| Re: REFORM: new subscripts must not change the number elements in array [message #90433 is a reply to message #90431] |
Mon, 02 March 2015 11:55 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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g.nacarts@gmail.com writes:
> I used the example provided by mo who said that 200*200=100*400. When a 2D array has dimensions [216,216] then 216*216=120*388.8
>
> when I tried a=reform(a,120l,388.8L,/overwrite) I got the old error
Are you familiar with "counting" numbers? 1,2,3,...
Array dimensions can only be specified with counting numbers. 388.8 is
real number, but not a counting number. You can pick any two counting
numbers to multiply together, so long as the TOTAL (also a counting
number) is the same counting number you get when you multiply the
original dimensions of the array together. Another way of saying this is
that when you reform (bend, shape, twist, etc.) an array, it can't end
up with more or less array elements then when you started.
If you DO want to end up with some other number of elements, then you
are going to have to REBIN your array, rather than REFORM it.
I say this in the most gentle way possible, but are you sure you are on
the right career path? I'm not sure math (and by extension computer
programming) is really going to be your thing. There is a way of
thinking and seeing the world that is required to write computer
programs that some people (no fault of their own!) just don't have. You
might be happier and less frustrated doing something that is more
closely related to your nature.
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thue. ("Perhaps thou speakest truth.")
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| Re: REFORM: new subscripts must not change the number elements in array [message #90443 is a reply to message #90427] |
Mon, 02 March 2015 23:26 |
Moritz Fischer
Messages: 32
Registered: June 2013
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Member |
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Am 02.03.2015 um 18:12 schrieb g.nacarts@gmail.com:
> Yes, I saw your last message but I am interested to understand how you end up before with the a = reform(a, 100l, 200l*2l, /overwrite).
Ok, let's try again.
What does reform do?
It changes the arrangement of the array elements. Not its total number.
In your initial example you had an array of 200 by 200 elements (40,000
in total), and you *can* reaarrange the elements of such an array to an
100 by 400 element array (also 40,000 in total), that is why I gave that
example.
Helder picked the same example by chance, I might as well have suggested
to reform it to 64 by 625 elements (also 40,000 in total).
Or to 100 by 16 by 25 elements.
> Then I tried to write it like this:
> a = reform(a, 120l, 216l*2l, /overwrite)
> but I got the error that I mentioned before.
Check the total element number: 120 by 216*2 = 120 by 432 = 51840
Your initial array randumu(s,216,216) has 216 by 216 = 46656 elements.
You say you want to go from 216x216 to 100x216x216.
You cannot do this with reform.
But of course you can do it differently. That would depend on what you
want to look the new array like. (Copies of the original, different data
of the same size, you name it. But do name it.)
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