Jeremy Bailin wrote:
> On Saturday, March 5, 2011 8:41:53 AM UTC-5, Gray wrote:
>> Hi all,
>>
>> I have a bunch of information which I'd like to store in an organized
>> fashion:
>> ~IDs of some stars
>> ~Stellar types
>> ~Magnitudes and fluxes in different images
>>
>> One way I could store the information would be as an array of
>> structures, with each element being a single star, but I don't a
>> priori know how many stars I have, and to find a particular star I'd
>> have to search on the ID element. So, I could use a HASH of
>> structures so I could index by ID, which would be ideal, but then
>> assigning values to the individual tags of the structures is much more
>> complicated. I could instead have a bunch of hashes, one for each type
>> of information, but that would get pretty unwieldy.
>>
>> So, IDL gurus, anyone have a suggestion for how to organize this most
>> efficiently and elegantly? Thanks!
>>
>> --Gray
>
> I haven't used hashes in idl, but I think that a hash of structures makes the most sense. What makes that too complicated?
Well, you wouldn't be able to access the individual elements of the structure values in the hash without first pulling
it out. E.g.
IDL> z=hash()
IDL> x={id:123,name:'blue',type:5,flux:3.14e+07}
IDL> z[x.id]=x
IDL> x={id:75,name:'red',type:5,flux:2.7e+07}
IDL> z[x.id]=x
IDL> help, z
Z HASH <ID=8 NELEMENTS=2>
IDL> print, z.keys()
123
75
Let's say I want to change the "type" of the added star with id 75 from 5 to 4, i.e. it is in error
IDL> help, z[75]
** Structure <95dd194>, 4 tags, length=24, data length=24, refs=4:
ID LONG 75
NAME STRING 'red'
TYPE LONG 5
FLUX FLOAT 2.70000e+07
I can't just do:
IDL> z[75].type = 4
% Illegal subscript range: Z.
% Error occurred at: $MAIN$
% Execution halted at: $MAIN$
I would have to extract it, change it, and then put it back:
IDL> a = z[75]
IDL> help, a
** Structure <95dd194>, 4 tags, length=24, data length=24, refs=3:
ID LONG 75
NAME STRING 'red'
TYPE LONG 5
FLUX FLOAT 2.70000e+07
IDL> a.type = 4
IDL> z[a.id] = a
IDL> print, z
123: { 123 blue 5 3.14000e+07}
75: { 75 red 4 2.70000e+07}
Now, while I don't think that's a particularly onerous thing to do, the OP might.
Not being an OOP expert I may be blowing smoke out of my proverbial, but I think the way IDL does this is The Better Way
- encapsulation and information hiding are the two OOP concepts that I find most frequently influence the way I write
code (OO and regular old procedural) such that it is reusable, extendable, and easily maintained.
cheers,
paulv
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