Re: plotting limitted range still going though all data

[<pl...@pi...>]

On 09/30/11 23:06, Ethan Merritt wrote:
> 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?
>
clearly it has to read the data lines but what needs evaluating, then 
range is a given constant.

It seems it is evaluation the using clause , yet this is not what the 
range applies to , it applies to $1.

Am I mistaken?

>> 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?
>