Re: plotting limitted range still going though all data

[Ethan M. <merritt@u.washington.edu>]

On Friday, September 30, 2011 12:20:57 pm pl...@pi... wrote:
> Hi,
> 
> I am calling a simple function max() to detect the two largest peaks in 
> the data.
> 
> 
> #function to do sample/hold
> max(x,y)=(ymax<y) ? ( xmax=x, ymax=y) :ymax ;
> 
> # dummy plot to scan data for biggest peak
> set term unknown
> plot ymax=xmax=0,  datafile using 1:( max(($1),($2)) );
> pk0=xmax; ymax=xmax=0;
> plot  [pk0+100:]  datafile using 1:( max(($1),($2)) );
> pk1=xmax;

> It's hitting the first one both times.

> Now unless I'm getting sleepy, this seems to show that the second call 
> to plot with a specified limited range is still going through the 
> motions. and evaluating the using clause for all data points in the 
> file. Thus all the mechanics are still being gone through only to have 
> null output created.

How would it know if $1 and/or $2 are out of range without
evaluating them first?

> Is this :
> 
> ?
> a) correctly what's happening
> b) necessary
> c) desirable.
> 
> ?
> 
> If I have a huge data file (that I do sometimes.) it would seem 
> advantageous if setting a range pre-empted the rest of plot activity 
> until the range condition is true.
> 
> Best regards. Peter.

If the values in column(1) are monotonic increasing in your data file,
then you can skip the leading N records via the "plot ... using every ..." 
option.  Otherwise each line will be processed and stored with flag 
INRANGE/OUTRANGE/UNDEFINED as appropriate.  After all the data records
are read in, the INRANGE points are plotted.  
Does that answer the question?

-- 
Ethan A Merritt
Biomolecular Structure Center,  K-428 Health Sciences Bldg
University of Washington, Seattle 98195-7742