| Re: Dynamically resizing arrays [message #42422 is a reply to message #42408] |
Sat, 05 February 2005 20:08   |
netnews.comcast.net
Messages: 10
Registered: October 2004
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Junior Member |
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Adding data row by row like this can be a little inefficient as you are
forcing IDL to allocate RAM for every iteration. I have found it to be
a bit quicker to grow the array in chunks appropriate for your application.
Taking Andrew's example:
array_init=INTARR(100,100) ; allocate 100 rows initially
nrows = 0
totrows = 100
while (have_new_data = 1) do begin
array_init[*,nrows] = your_row_of_data
++nrows
; grow array if needed - adding 100 rows at a time
if (nrows eq totrows - 1) then begin
array_init = [[array_init],[INTARR(100,100)]]
totrows = totrows + 100
endif
endwhile
; trim array when done adding data
array_init = array_init[*,nrows - 1]
You have a little more to keep track of but for larger arrays it will be
worth the hassle.
-Rick
Andrew wrote:
> Hi Jonathan,
>
> Assume you have declared your initial array, lets call it array_init
>
> array_init=INTARR(100) ;for arguments sake
>
> if we now assume that you are in the loop and want to append the new
> data, which we also assume is 100 columns long (i.e fixed length)
>
> new_row=intarr(100) ;the array of new data
> FOR i=0,99 DO BEGIN
> ;some operation or whatever you do here
> ;to place the data in new_row
>
> array_init=[[array_init],[new_row]] ;appened it to the original data
> ENDFOR
>
> your array_init will now grow one row at a time with each loop. You
> might want to consider using a WHILE statement though to avoid the FOR
> loop. I hope this helps, and is correct. Try it with some dummy arrays
> (I did).
>
> Cheers
> Andrew
>
> Jonathan Greenberg wrote:
>
>> I was hoping to get some feedback on the best way of creating a
>
> "database"
>
>> -- an array of fixed columns but unknown number of rows which will be
>> appended to within some sort of loop. What is the best way of doing
>
> this?
>
>> --j
>
>
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