| basic array-structure understanding question [message #63682] |
Wed, 19 November 2008 06:21  |
julia.walterspiel
Messages: 35
Registered: July 2008
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Member |
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hi everybody
This is what does not get into my head:
I have one array containing my data.
I have a second array containing the times when the data was
collected.
They have the same lenght.
I put them into one structure because we all like structures and I
learned about their advantages.
now:
IN SHORT are those arrays linked somehow? in other words: when working
with a structure, does IDL know which value matches the corresponding
date, given the data and the date array have the same length. Are
those arrays somehow connected or are they completely independent from
each other?
IN LONG: if I want to get e.g. all the data from all Januarys from
2000 to 2007, can I do it somehow like
all_jan = structure.data (where(structure.time EQ 200?01??????) )..
then it would automatically "select" only the right values. (and then
I would have to make a separate array of the corresponding dates, make
those two new arrays a structure so that I can plot data vs. date all
in one?)
or do I have to do it via some indexing, like:
all_jan = where (structure.time EQ 200?01??????) )
and then apply the index to my array of data?
jeez, i'm real slow on the uptake here.. sorry for bothering you with
such simple questions, but can anybody help me undo this big knot in
my brain?
cheers,
juls
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| Re: basic array-structure understanding question [message #63799 is a reply to message #63682] |
Wed, 19 November 2008 07:10  |
Kenneth P. Bowman
Messages: 585
Registered: May 2000
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Senior Member |
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In article
<68a3f7b5-1c15-4dbb-bf83-b019eb7dd204@g17g2000prg.googlegroups.com>,
julia.walterspiel@gmail.com wrote:
> hi everybody
>
> This is what does not get into my head:
>
> I have one array containing my data.
> I have a second array containing the times when the data was
> collected.
> They have the same lenght.
>
> I put them into one structure because we all like structures and I
> learned about their advantages.
>
> now:
>
> IN SHORT are those arrays linked somehow? in other words: when working
> with a structure, does IDL know which value matches the corresponding
> date, given the data and the date array have the same length. Are
> those arrays somehow connected or are they completely independent from
> each other?
>
>
> IN LONG: if I want to get e.g. all the data from all Januarys from
> 2000 to 2007, can I do it somehow like
>
> all_jan = structure.data (where(structure.time EQ 200?01??????) )..
> then it would automatically "select" only the right values. (and then
> I would have to make a separate array of the corresponding dates, make
> those two new arrays a structure so that I can plot data vs. date all
> in one?)
>
> or do I have to do it via some indexing, like:
> all_jan = where (structure.time EQ 200?01??????) )
>
> and then apply the index to my array of data?
>
>
> jeez, i'm real slow on the uptake here.. sorry for bothering you with
> such simple questions, but can anybody help me undo this big knot in
> my brain?
> cheers,
> juls
An IDL structure is just a container, into which you can put a
collection of (related) variables. Then you can pass the
structure around, instead of having to pass all of the variables
individually.
IDL> x = findgen(10)^3
IDL> i = lindgen(10)
IDL> str = {x:x, i:i}
IDL> help, str, /str
** Structure <1db1314>, 2 tags, length=80, data length=80, refs=1:
X FLOAT Array[10]
I LONG Array[10]
IDL> help, str.x
<Expression> FLOAT = Array[10]
IDL> help, str.i
<Expression> LONG = Array[10]
IDL> plot, str.i, str.x
IDL> even = where((str.i MOD 2) eq 0) ;Find even indices
IDL> print, even
0 2 4 6 8
IDL> oplot, str.i[even], str.x[even], psym = -1 ;Plot even indices only
Ken Bowman
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| Re: basic array-structure understanding question [message #63863 is a reply to message #63778] |
Thu, 20 November 2008 06:43 |
pgrigis
Messages: 436
Registered: September 2007
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Senior Member |
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julia.waltersp...@gmail.com wrote:
>>
>> eth?
>
>
> war an der ETH/Uni ZH, jetzt an der MeteoSchweiz (Pendant zum DWD),
> und die arbeiten "leider" nicht mit Matlab sondern IDL.. back to
> square one
Ich wusste gar nicht, dass Meteosuisse IDL benutzt...
Mein Vertrauen in Wetterprognoses ist jetezt
ein bisschen gesunken ;-)
Liebe Gruesse aus Boston
Paolo Grigis (ehemalig doktorand an der ETH)
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