| Re: How to read file to fill an array "partially" ? [message #56185] |
Tue, 16 October 2007 18:25  |
ben.bighair
Messages: 221
Registered: April 2007
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Senior Member |
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On Oct 16, 5:19 pm, mystea <idllear...@gmail.com> wrote:
> 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.
Hi,
Yes, you are right that IDL needs to read into a variable and not into
an expression. David Fanning has a very good article on this -
see ...
http://dfanning.com/tips/read_subscripted_array.html
But while you are at it, you mention that you have a lot of these.
This might be a great chance to store each array as an object, and
then store the collection of these array objects in an container. I
have pasted below code that will do just that plus it will read in
your file automatically.
Here's what a session in IDL might look like using these objects which
i call "Bucket" which will hold an array and "MyBigBucket" will will
hold a bunch of the little buckets.
IDL> o = obj_new("mybigbucket", "myarray.txt")
% Compiled module: MYBIGBUCKET__DEFINE.
Reading a 5 element array
0=7.7
1=8.1
2=9.0
3=1.1
4=3.0
Reading a 3 element array
0=2.2
1=1.0
2=2.2
IDL> x = o->Get(1)
IDL> help, x
X OBJREF = <ObjHeapVar62(BUCKET)>
IDL> print, x->get()
2.20000 1.00000 2.20000
IDL> print, x->get(2)
2.20000
And here's the code which you mst save in your search path as
"mybigbucket__define.pro"
**BEGIN
;******
; BUCKET is simply a pointer manager - acts as a bucket to place
anything
;******
; returns the number of elements in data
FUNCTION Bucket::Count
return, self->Size(/N_ELEMENTS)
END
;returns results of SIZE call on data
FUNCTION Bucket::Size, $
_EXTRA = extra
IF PTR_VALID(self.pData) Then $
RETURN, SIZE(*self.pData, _EXTRA = extra) Else $
RETURN, SIZE(dummy, _EXTRA = extra)
END
;gets the pointer to the data (be careful)
FUNCTION Bucket::GetPointer
Return, self.pData
END;GetPointer
;returns the data or the ith elements of data
FUNCTION Bucket::Get, i, COUNT = count
count = PTR_VALID(self.pData)
if count EQ 0 then Return, -1
count = n_elements(*self.pData)
if count EQ 0 then return, -1
if n_elements(i) NE 0 then Begin
d = (*Self.pData)[i]
count = n_elements(d)
return, d
EndIf Else Begin
return, *self.pData
EndElse
END ;get
;sets the data
PRO Bucket::Set, data
if PTR_VALID(self.Pdata) EQ 0 then $
self.pData = PTR_NEW(data) Else $
*self.pData = data
END
;init
FUNCTION Bucket::Init, data
if n_elements(data) NE 0 then self->Set, data
Return, 1
END
;cleanup
PRO Bucket::Cleanup
PTR_FREE, self.pData
END
;definition
PRO Bucket__Define, struct
struct = {Bucket, $
pData: PTR_NEW()}
END
;*****************
; MyBigBucket - a container for the smallerbuckets
;*****************
PRO MyBigBucket::ReadFile, file
if n_elements(file) EQ 0 then file = self.file
testfile = FILE_SEARCH(file[0], COUNT = nFile)
if nFile EQ 0 then message, 'File not found: ' + file[0]
lines = (FILE_LINES(testFile[0]))[0]
OPENR, LUN, testFile[0], /GET_LUN
N = '0'
DUMMY = ''
Repeat Begin
ReadF, LUN, N, format = '(A1)'
READF, LUN, dummy, format = '(A1)' ;this is blank line
PRINT, 'Reading a ' + N + ' element array'
arr = FLTARR(LONG(N))
for i = 0, LONG(n)-1 do begin
READF, LUN, dummy
print, STRTRIM(i,2) + "="+dummy
arr[i] = FLOAT(dummy)
endfor
self->Add, OBJ_NEW('Bucket', arr)
if(eof(LUN) EQ 0) then $
READF, LUN, dummy, format = '(A1)' else $ ;this is blank line
BREAK
EndRep Until (eof(LUN) EQ 1)
FREE_LUN, LUN
self.file = testFile[0]
END ;ReadFile
FUNCTION MyBigBucket::Get, pos, _REF_EXTRA = extra
return, self->IDL_CONTAINER::Get(position = pos, _EXTRA = extra)
END
FUNCTION MyBigBucket::Init, file
if self->IDL_Container::Init() EQ 0 then return, 0
if n_elements(file) NE 0 then self->ReadFile, file
return, 1
END
PRO MyBigBucket::Cleanup
self->IDL_CONTAINER::Cleanup
END
PRO MyBigBucket__Define, struct
struct = {MyBigBucket, $
INHERITS IDL_CONTAINER, $
FILE: ""}
END
**END
Cheers,
Ben
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| Re: How to read file to fill an array "partially" ? [message #56375 is a reply to message #56185] |
Wed, 17 October 2007 11:26  |
mystea
Messages: 16
Registered: October 2007
|
Junior Member |
|
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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
On Oct 16, 6:25 pm, "ben.bighair" <ben.bigh...@gmail.com> wrote:
> On Oct 16, 5:19 pm, mystea <idllear...@gmail.com> wrote:
>
>
>
>> 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.
>
> Hi,
>
> Yes, you are right that IDL needs to read into a variable and not into
> an expression. David Fanning has a very good article on this -
> see ...
>
> http://dfanning.com/tips/read_subscripted_array.html
>
> But while you are at it, you mention that you have a lot of these.
> This might be a great chance to store each array as an object, and
> then store the collection of these array objects in an container. I
> have pasted below code that will do just that plus it will read in
> your file automatically.
>
> Here's what a session in IDL might look like using these objects which
> i call "Bucket" which will hold an array and "MyBigBucket" will will
> hold a bunch of the little buckets.
>
> IDL> o = obj_new("mybigbucket", "myarray.txt")
> % Compiled module: MYBIGBUCKET__DEFINE.
> Reading a 5 element array
> 0=7.7
> 1=8.1
> 2=9.0
> 3=1.1
> 4=3.0
> Reading a 3 element array
> 0=2.2
> 1=1.0
> 2=2.2
> IDL> x = o->Get(1)
> IDL> help, x
> X OBJREF = <ObjHeapVar62(BUCKET)>
> IDL> print, x->get()
> 2.20000 1.00000 2.20000
> IDL> print, x->get(2)
> 2.20000
>
> And here's the code which you mst save in your search path as
> "mybigbucket__define.pro"
>
> **BEGIN
>
> ;******
> ; BUCKET is simply a pointer manager - acts as a bucket to place
> anything
> ;******
> ; returns the number of elements in data
> FUNCTION Bucket::Count
> return, self->Size(/N_ELEMENTS)
> END
> ;returns results of SIZE call on data
> FUNCTION Bucket::Size, $
> _EXTRA = extra
> IF PTR_VALID(self.pData) Then $
> RETURN, SIZE(*self.pData, _EXTRA = extra) Else $
> RETURN, SIZE(dummy, _EXTRA = extra)
> END
> ;gets the pointer to the data (be careful)
> FUNCTION Bucket::GetPointer
> Return, self.pData
> END;GetPointer
> ;returns the data or the ith elements of data
> FUNCTION Bucket::Get, i, COUNT = count
> count = PTR_VALID(self.pData)
> if count EQ 0 then Return, -1
> count = n_elements(*self.pData)
> if count EQ 0 then return, -1
> if n_elements(i) NE 0 then Begin
> d = (*Self.pData)[i]
> count = n_elements(d)
> return, d
> EndIf Else Begin
> return, *self.pData
> EndElse
> END ;get
> ;sets the data
> PRO Bucket::Set, data
> if PTR_VALID(self.Pdata) EQ 0 then $
> self.pData = PTR_NEW(data) Else $
> *self.pData = data
> END
> ;init
> FUNCTION Bucket::Init, data
> if n_elements(data) NE 0 then self->Set, data
> Return, 1
> END
> ;cleanup
> PRO Bucket::Cleanup
> PTR_FREE, self.pData
> END
> ;definition
> PRO Bucket__Define, struct
> struct = {Bucket, $
> pData: PTR_NEW()}
> END
>
> ;*****************
> ; MyBigBucket - a container for the smallerbuckets
> ;*****************
>
> PRO MyBigBucket::ReadFile, file
>
> if n_elements(file) EQ 0 then file = self.file
>
> testfile = FILE_SEARCH(file[0], COUNT = nFile)
> if nFile EQ 0 then message, 'File not found: ' + file[0]
> lines = (FILE_LINES(testFile[0]))[0]
> OPENR, LUN, testFile[0], /GET_LUN
> N = '0'
> DUMMY = ''
> Repeat Begin
> ReadF, LUN, N, format = '(A1)'
> READF, LUN, dummy, format = '(A1)' ;this is blank line
> PRINT, 'Reading a ' + N + ' element array'
> arr = FLTARR(LONG(N))
> for i = 0, LONG(n)-1 do begin
> READF, LUN, dummy
> print, STRTRIM(i,2) + "="+dummy
> arr[i] = FLOAT(dummy)
> endfor
> self->Add, OBJ_NEW('Bucket', arr)
> if(eof(LUN) EQ 0) then $
> READF, LUN, dummy, format = '(A1)' else $ ;this is blank line
> BREAK
> EndRep Until (eof(LUN) EQ 1)
>
> FREE_LUN, LUN
> self.file = testFile[0]
> END ;ReadFile
>
> FUNCTION MyBigBucket::Get, pos, _REF_EXTRA = extra
> return, self->IDL_CONTAINER::Get(position = pos, _EXTRA = extra)
> END
> FUNCTION MyBigBucket::Init, file
> if self->IDL_Container::Init() EQ 0 then return, 0
> if n_elements(file) NE 0 then self->ReadFile, file
> return, 1
> END
>
> PRO MyBigBucket::Cleanup
> self->IDL_CONTAINER::Cleanup
> END
>
> PRO MyBigBucket__Define, struct
> struct = {MyBigBucket, $
> INHERITS IDL_CONTAINER, $
> FILE: ""}
> END
>
> **END
>
> Cheers,
> Ben
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