| Re: Plotting one point per loop [message #91397 is a reply to message #91393] |
Wed, 08 July 2015 11:33   |
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Paul Van Delst[1]
Messages: 1157
Registered: April 2002
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Senior Member |
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On 07/08/15 13:52, wdolan@oxy.edu wrote:
> Hi Paul,
>
> It is set to plot to a postscript file. That seems like a good idea,
> but I am not sure how to store those values until the end. Because if
> I did an array, I would have to specify a size, and each run has a
> different number of scans.
Fair enough.
Craig answered your actual question (thank goodness! :o). I went off on
a tangent about efficient ways to increase array sizes when you don't
know the final size, so that you can then plot (mostly because you said
you were a new user :o)
Keep reading only for sh*ts and giggles.
As an exercise (my actual work today is a bit repetitive) I came up with
the code way down below. When I run it I get the following:
IDL> .run blah.pro
% Compiled module: $MAIN$.
% Time elapsed: 16.238165 seconds.
X FLOAT = Array[300000]
% Time elapsed: 0.20202398 seconds.
X FLOAT = Array[300000]
The doubling method is pretty efficient. Way better than simple
concatenation. If you increase the number of scans to 1000000 then the
first method will be done sometime tomorrow....
; The (generally unknown) number of scans for this example
n_scans = 300000L
; METHOD #1: CONTINUALLY CONCATENATE ONTO ARRAY
; Specify an empty array
x = []
; Loop over your (unknown) number of scans
scan_count = 0
tic
repeat begin
; Keep track of the scan count
scan_count++
; Accumulate an array of numbers to plot
x = [x,randomn(seed,1)]
endrep until scan_count eq n_scans
toc
help, x
; METHOD #2: DOUBLE SIZE OF ARRAY AS NEEDED
; (HAM FISTED CODE, BUT YOU GET THE IDEA)
; Specify an empty array and initial size
n_size = 10000L
x = fltarr(1000)
; Loop over your (unknown) number of scans
scan_count = 0
tic
repeat begin
; Keep track of the scan count
scan_count++
; Double array size if necessary
if ( n_elements(x) lt scan_count ) then begin
n = n_elements(x)
x = [temporary(x),fltarr(n)]
endif
; Insert value into array
x[scan_count-1] = randomn(seed,1)
endrep until scan_count eq n_scans
; Truncate array as necessary
x = x[0:scan_count-1]
toc
help, x
end
cheers,
paulv
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