| Re: Subscripting multidimensional arrays [message #37269] |
Fri, 12 December 2003 13:35  |
JD Smith
Messages: 850
Registered: December 1999
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Senior Member |
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On Fri, 12 Dec 2003 14:15:33 -0700, Christopher Lee wrote:
> JD Smith wrote:
>> On Fri, 12 Dec 2003 07:55:16 -0700, Christopher Lee wrote:
> <snip>
>>
>> PRODUCT works nicely for this:
>>
>> function linear_indices,array,vec_indices
>> s=size(array,/DIMENSIONS)
>> nd=n_elements(s)
>> if nd eq 1 then return,s[0]
>
> ;you mean "return ,vec_indices" , yes?
Whoops, yes, sorry:
if nd eq 1 then return, vec_indices[0]
>> return,long(total([1.,product(s[0:nd-1],/CUMULATIVE)]*vec_in dices))
>> end
>
> PRODUCT doesn't seem to exist on my IDL installations (5.3->5.6
> inclusive), is it an IDL 6 thing? I've written my own obviously, but not
> with CUMULATIVE. Hopefully the IDL 6 licence will work on Monday.>
Strange, it shipped with IDL5.6.
>
>
>> to go the other direction, IDL6 offers ARRAY_INDICES. Or you can
>> always just resort to:
>>
>> a[vec[0],vec[1],vec[2]]
>>
>>
> Ahem, oops. Apparently I used a cluster bomb to open a can of beans...a
> switch case statement would take care of the dimensions upto the IDL
> limit of 8 dimensions, or using IDL's ability to ignore trailing
> dimensions if they're 0 hack to use 8 dimensions every time.
Yes, but that would be ugly ;). What if IDL increases the 8-dim limit in
the future?
JD
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| Re: Subscripting multidimensional arrays [message #37271 is a reply to message #37269] |
Fri, 12 December 2003 13:15  |
Chris Lee
Messages: 101
Registered: August 2003
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Senior Member |
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JD Smith wrote:
> On Fri, 12 Dec 2003 07:55:16 -0700, Christopher Lee wrote:
<snip>
>
> PRODUCT works nicely for this:
>
> function linear_indices,array,vec_indices
> s=size(array,/DIMENSIONS)
> nd=n_elements(s)
> if nd eq 1 then return,s[0]
;you mean "return ,vec_indices" , yes?
> return,long(total([1.,product(s[0:nd-1],/CUMULATIVE)]*vec_in dices))
> end
PRODUCT doesn't seem to exist on my IDL installations (5.3->5.6
inclusive), is it an IDL 6 thing? I've written my own obviously, but not
with CUMULATIVE. Hopefully the IDL 6 licence will work on Monday.
>
> to go the other direction, IDL6 offers ARRAY_INDICES. Or you can always
> just resort to:
>
> a[vec[0],vec[1],vec[2]]
>
Ahem, oops. Apparently I used a cluster bomb to open a can of beans...a
switch case statement would take care of the dimensions upto the IDL
limit of 8 dimensions, or using IDL's ability to ignore trailing
dimensions if they're 0 hack to use 8 dimensions every time.
> A take home problem would be to modify this such that NxM input vectors,
> where N is the number of dimensions of "array", will return a vector of
> length M containing all the 1-D indices. Hints: REBIN/REFORM and the
> "dimension" argument to TOTAL.
>
I got that exercise too, but I thought I'd leave some fun for other
people :) plus I always get into a "but what if I wanted the input
vector to be MxN" and "what if not enough arguments are supplied, or
they're out of bounds" and I remember I have work to do, sometimes.
> JD
Chris.
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| Re: Subscripting multidimensional arrays [message #37275 is a reply to message #37274] |
Fri, 12 December 2003 11:44 |
R.G. Stockwell
Messages: 363
Registered: July 1999
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Senior Member |
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"R.G. Stockwell" <noemail@please.com> wrote in message
news:5smCb.14$SO3.23741@news.uswest.net...
>
> This will work if you always have a 3D array (or do you want to be able to
> index with an array for an arbitary size array?)
ok, just for kicks, for arbitary array and location vector:
(here I use "loc" as the location vector, i.e. loc = [2,2,1] )
execode = execute('result =
a['+string(loc,format='('+string(n_elements(loc))+'(I,:,",")) ')+']')
print,result
Cheers,
bob
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| Re: Subscripting multidimensional arrays [message #37278 is a reply to message #37275] |
Fri, 12 December 2003 08:53 |
JD Smith
Messages: 850
Registered: December 1999
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Senior Member |
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On Fri, 12 Dec 2003 07:55:16 -0700, Christopher Lee wrote:
> In article <nwfCb.37807$SU2.20541@newssvr29.news.prodigy.com>, "Jonathan
> Greenberg" <greenberg@ucdavis.edu> wrote:
>
>
>> Hi all -- I was hoping to get some help with converting a vector which
>> contains the x,y,z position for a value I want to exract from a
>> multidimensional array -- I understand that using an array to subscript
>> another array requires knowing the linear subscript position. For
>> example: a = 0 10 20
>> 30 40 50
>> 60 70 80
>>
>> 90 100 110
>> 120 130 140
>> 150 160 170
>> I have a vector which is defined as:
>> locationvector=[2,2,2]
>> I want to extract the value at that position (e.g. a[2,2,2] = 170), but
>> I can't do a:
>> a[locationvector] --> I apparently have to convert the locationvector
>> to that linear position. How do I do this? Does IDL have a built in
>> function that will do this conversion, or is there an easy formula for
>> doing this conversion in ANY dimension? Thanks! --j
>>
>>
> function element, array, loc_vector
>
> s=size(array)
> d=s[1:s[0]] ;dimensions
> e=lonarr(s[0]) ;product of dimensions e[0]=1L for i=1L, s[0]-1 do
> e[i]=e[i-1]*d[i-1] ;e is the number of elements each dimension contains
> return, total(loc_vector*e)
>
> end
>
> seems to work, there must be a better way though...
PRODUCT works nicely for this:
function linear_indices,array,vec_indices
s=size(array,/DIMENSIONS)
nd=n_elements(s)
if nd eq 1 then return,s[0]
return,long(total([1.,product(s[0:nd-1],/CUMULATIVE)]*vec_in dices))
end
to go the other direction, IDL6 offers ARRAY_INDICES. Or you can always
just resort to:
a[vec[0],vec[1],vec[2]]
A take home problem would be to modify this such that NxM input vectors,
where N is the number of dimensions of "array", will return a vector of
length M containing all the 1-D indices. Hints: REBIN/REFORM and the
"dimension" argument to TOTAL.
JD
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| Re: Subscripting multidimensional arrays [message #37280 is a reply to message #37278] |
Fri, 12 December 2003 08:57 |
R.G. Stockwell
Messages: 363
Registered: July 1999
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Senior Member |
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"Jonathan Greenberg" <greenberg@ucdavis.edu> wrote in message
news:nwfCb.37807$SU2.20541@newssvr29.news.prodigy.com...
> Hi all -- I was hoping to get some help with converting a vector which
> contains the x,y,z position for a value I want to exract from a
> multidimensional array -- I understand that using an array to subscript
> another array requires knowing the linear subscript position. For
example:
>
> a = 0 10 20
> 30 40 50
> 60 70 80
>
> 90 100 110
> 120 130 140
> 150 160 170
>
> I have a vector which is defined as:
> locationvector=[2,2,2]
>
> I want to extract the value at that position (e.g. a[2,2,2] = 170), but I
> can't do a:
> a[locationvector] --> I apparently have to convert the locationvector to
> that linear position. How do I do this? Does IDL have a built in
function
> that will do this conversion, or is there an easy formula for doing this
> conversion in ANY dimension? Thanks!
>
> --j
The straightforward way is:
result=a[locationvector[0],locationvector[1],locationvector[ 2]]
This will work if you always have a 3D array (or do you want to be able to
index with an array for an arbitary size array?)
Also, your location vector should be [2,2,1] in the above example.
Cheers,
bob
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| Re: Subscripting multidimensional arrays [message #37284 is a reply to message #37278] |
Fri, 12 December 2003 06:55 |
Chris Lee
Messages: 101
Registered: August 2003
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Senior Member |
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In article <nwfCb.37807$SU2.20541@newssvr29.news.prodigy.com>, "Jonathan
Greenberg" <greenberg@ucdavis.edu> wrote:
> Hi all -- I was hoping to get some help with converting a vector which
> contains the x,y,z position for a value I want to exract from a
> multidimensional array -- I understand that using an array to subscript
> another array requires knowing the linear subscript position. For
> example: a = 0 10 20
> 30 40 50
> 60 70 80
>
> 90 100 110
> 120 130 140
> 150 160 170
> I have a vector which is defined as:
> locationvector=[2,2,2]
> I want to extract the value at that position (e.g. a[2,2,2] = 170), but
> I can't do a:
> a[locationvector] --> I apparently have to convert the locationvector to
> that linear position. How do I do this? Does IDL have a built in
> function that will do this conversion, or is there an easy formula for
> doing this conversion in ANY dimension? Thanks! --j
>
function element, array, loc_vector
s=size(array)
d=s[1:s[0]] ;dimensions
e=lonarr(s[0]) ;product of dimensions
e[0]=1L
for i=1L, s[0]-1 do e[i]=e[i-1]*d[i-1]
;e is the number of elements each dimension contains
return, total(loc_vector*e)
end
;;test
a=findgen(4,5,6)
;in this example, e=[1,4,20]
b=[2,3,4]
print, a[2,3,4], a[element(a,b)]
94.000 94.000
seems to work, there must be a better way though...
Chris.
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| Re: Subscripting multidimensional arrays [message #37401 is a reply to message #37278] |
Sat, 13 December 2003 12:19 |
Jonathan Greenberg
Messages: 91
Registered: November 2002
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Member |
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Hey all, JDs nice little function worked great (thanks! i give you credit
in the classifier i'm coding right now -- don't worry, its not commercial)--
i did notice there was an 8-d limitation on arrays, but you could get by the
by just making your own subscripts, since, as this little process has shown,
the arrays are unidimensional in nature anyway... (e.g. there really isn't a
functional difference, as I understand it, between:
1 2
3 4
and
1 2 3 4
You just need to know the order of subscript indexing...
--j
"JD Smith" <jdsmith@as.arizona.edu> wrote in message
news:pan.2003.12.12.16.53.23.571408.24862@as.arizona.edu...
> On Fri, 12 Dec 2003 07:55:16 -0700, Christopher Lee wrote:
>
>> In article <nwfCb.37807$SU2.20541@newssvr29.news.prodigy.com>, "Jonathan
>> Greenberg" <greenberg@ucdavis.edu> wrote:
>>
>>
>>> Hi all -- I was hoping to get some help with converting a vector which
>>> contains the x,y,z position for a value I want to exract from a
>>> multidimensional array -- I understand that using an array to subscript
>>> another array requires knowing the linear subscript position. For
>>> example: a = 0 10 20
>>> 30 40 50
>>> 60 70 80
>>>
>>> 90 100 110
>>> 120 130 140
>>> 150 160 170
>>> I have a vector which is defined as:
>>> locationvector=[2,2,2]
>>> I want to extract the value at that position (e.g. a[2,2,2] = 170), but
>>> I can't do a:
>>> a[locationvector] --> I apparently have to convert the locationvector
>>> to that linear position. How do I do this? Does IDL have a built in
>>> function that will do this conversion, or is there an easy formula for
>>> doing this conversion in ANY dimension? Thanks! --j
>>>
>>>
>> function element, array, loc_vector
>>
>> s=size(array)
>> d=s[1:s[0]] ;dimensions
>> e=lonarr(s[0]) ;product of dimensions e[0]=1L for i=1L, s[0]-1 do
>> e[i]=e[i-1]*d[i-1] ;e is the number of elements each dimension contains
>> return, total(loc_vector*e)
>>
>> end
>>
>> seems to work, there must be a better way though...
>
> PRODUCT works nicely for this:
>
> function linear_indices,array,vec_indices
> s=size(array,/DIMENSIONS)
> nd=n_elements(s)
> if nd eq 1 then return,s[0]
> return,long(total([1.,product(s[0:nd-1],/CUMULATIVE)]*vec_in dices))
> end
>
> to go the other direction, IDL6 offers ARRAY_INDICES. Or you can always
> just resort to:
>
> a[vec[0],vec[1],vec[2]]
>
> A take home problem would be to modify this such that NxM input vectors,
> where N is the number of dimensions of "array", will return a vector of
> length M containing all the 1-D indices. Hints: REBIN/REFORM and the
> "dimension" argument to TOTAL.
>
> JD
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