| How to read file to fill an array "partially" ? [message #56187] |
Tue, 16 October 2007 14:19  |
mystea
Messages: 16
Registered: October 2007
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Junior Member |
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Hello All,
I am trying to read data from an ASCII file. The format of the file is
as follows.
"mydata.txt":
5
7.7
8.1
9.0
1.1
3.0
3
2.2
1.0
2.2
Namely, the first line tells you how many entries are there, and the
data follows. I plan to save them in a 2*5 array "myarray." So the
following is what I am doing:
openr, lun, 'mydata.txt', /get_lun ;open file
myarray=dblarr(2,5) ;declare array to
store data
n_entries=0S ;declare variable
to store number of entries
for i=0, 1 do begin ;try to fill
"myarray" by a for loop
readf, lun, n_entries ;read in # of
entries
n_entries=fix(n_entries-1S) ;the final index of
valid entry is # of entries minus one.
readf, lun, myarray[i,0:n_entries] ;read data into
myarray[i,0:# of entries -1]
endfor
However, it does not work! All I get is 0.00000 for all the entries I
have. (data does not seem to be read)
I tried to use format code, it doesn't help either. However, the
terminal replies:
% Attempt to store into an expression: <DOUBLE Array[5]>.
so I guess IDL does not allow data to be read to stuff like
myarray[0,0:4] because it is an "expression" instead of a real array.
I have three simple questions:
1. How to read data and stored partially to an array?
2. Why the response "% Attempt to store into an expression" does not
show up when I wasn't offering formats?
3. (might be the answer to the first question) How can I find the
reference address of a certain portion of an array?
P.S.Of course my data is much larger, I modified them to 2*5 in order
to make the case clearer.
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| Re: How to read file to fill an array "partially" ? [message #56368 is a reply to message #56187] |
Wed, 17 October 2007 17:13  |
ben.bighair
Messages: 221
Registered: April 2007
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Senior Member |
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On Oct 17, 2:26 pm, mystea <idllear...@gmail.com> wrote:
> Hi Ben,
>
> Thanks a lot for providing the link and your code.
> I have two observations when I tried out David's ASCII reading tips.
>
> 1. the format code '(I0)' means integer of any length while '(A0)'
> literally means string of length zero.
> 2. A string can't start with a number. for example, if you type
> junk="3", IDL returns syntax error. The best one can do seems to be
> junk=" 3".
>
> Although I can swallow it and take them as simple facts, I don't feel
> very comfortable about it. Why is there such inconsistency in the
> design of format codes? And what can you do if you really want your
> string starts with a number?
>
> As to your bucket code, I need a little more time to digest. Do you
> recommend any reference in IDL object programming?
>
> Sincerely,
>
> Gene
Hi Gene,
The best place to research is this newsgroup! You did search here
first, right? I tried searching this group via groups.google for
"objects" and this http://tinyurl.com/3bvg7d looks promising to me.
If you plan on writing a lot of IDL code then I can assure you that
your time will be well spent learning IDL's OO stuff. Having
subsequently worked with other OO languages I can only now begin to
see the strengths and weaknesses of IDL's OO implementation. I would
say the 95% of my IDL code is now OO. I especially like it for working
with complex files (headers as well as data), widgets (I can't even
remember how to do it without objects), and command line interaction
(which is paradoxical in a way.)
What jumped out to me about your problem was that you indicated your
data lumps might be different sizes. To keep all those lumps
associated together you just have to use IDL heap variable pointers -
other wise it is a mess. Now I can never remember when to use *data vs
*(data) vs ... So, long ago I simply squished all that stuff into an
object and wrote something like the BUCKET object with GET and SET
methods. Write once - use over and over and over again. That is
pretty darned handy.
MyBigBucket is simply to contain all the little buckets. Maybe I
should have called it "dumptruck" or or "wheelbarrow" or something
like that. You don't have to use that as you could use an object
array instead.
So you should definitely wade into OO. You won't regret it.
Cheers,
Ben
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| Re: How to read file to fill an array "partially" ? [message #56374 is a reply to message #56187] |
Wed, 17 October 2007 11:31 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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mystea writes:
> 2. A string can't start with a number. for example, if you type
> junk="3", IDL returns syntax error. The best one can do seems to be
> junk=" 3".
>
> Although I can swallow it and take them as simple facts, I don't feel
> very comfortable about it. Why is there such inconsistency in the
> design of format codes? And what can you do if you really want your
> string starts with a number?
You will have to use single quotes for your numbers:
s = '3'
Variables that start with a double quote (var = "3) are
taken to be octal values.
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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