[proFit-list] Finding the min or max of data
Chris Lee
laserboy at fusemail.com
Fri May 10 11:45:42 CDT 2013
If you are comparing exact values then the equality should always work. I agree that if you were to compute two values using different function calls then comparing for equality is a bad idea, but, if a function reads the same value from a table twice and an equality test fails, I would be worried.
I don't think that the pro fit compiler optimizes all that well, so I would expect that internal code that loops is faster than compiled pascal that loops. Likewise, the numpy.argmax() function must loop internally, but it is amazingly fast, and no matter how long an array is, I've never observed a delay in the function call.
Cheers
Chris
On 10 May 2013 (W: 19), at 16:40, Davide Guarisco <guarisco at sbcglobal.net> wrote:
>
> On May 10, 2013, at 1:41 AM, Chris Lee wrote:
>
>> Why not call the statistics function first to determine the min and max. Then, in the loop, check for equality?
>
>
> Two reasons:
> 1. With floating point numbers, equality check is always tricky
> 2. The Statistics function also will have to loop through the data to find min and max. It should be more efficient to loop through the data once. This assumes that the compiled proFit programs and "native" Statistics functions run equally fast. That may not be the case.
>
> Davide
>
>
>
>
>
>>
>> I am responsible for the concept of this message. Autocorrect is responsible for the contents.
>>
>> On 10/05/2013, at 5:15 AM, Davide Guarisco <guarisco at sbcglobal.net> wrote:
>>
>>> Then you have never dealt with large amount of data. I do, and I can assure you that pro Fit takes an awfully long time to sort a substantial data file (when it doesn't hang).
>>>
>>> But I happen to have a fondness for good and efficient programming, and sorting really isn't the way to solve this problem. The best sorting algorithms behave as O(n log n), whereas this problem can be solved in O(n).
>>>
>>>
>>> Consider this simple code:
>>>
>>> procedure findminmax(var xmin,xmax: extended;var imin,imax: integer);
>>> {Finds the minimum (xmin), maximum (xmax) values and their indices of the Y column of the current data window}
>>> var ymin,ymax,yx: extended;
>>> i: integer;
>>>
>>> begin
>>> ymin:=InvalidNum;
>>> ymax:=InvalidNum;
>>> imin:=InvalidNum;
>>> imax:=InvalidNum;
>>> {Find first valid data}
>>> for i:=1 to NrRows do
>>> if not(invalid(data[i,YColumn])) then
>>> begin
>>> ymin:=data[i,YColumn];
>>> ymax:=ymin;
>>> imin:=i;
>>> imax:=imin;
>>> Leave;
>>> end;
>>> for i:=i+1 to NrRows do
>>> begin
>>> if not(invalid(data[i,YColumn])) then
>>> begin
>>> yx:=data[i,YColumn];
>>> if yx>ymax then
>>> begin
>>> ymax:=yx;
>>> imax:=i
>>> end
>>> else
>>> if yx<ymin then
>>> begin
>>> ymin:=yx;
>>> imin:=i
>>> end;
>>> end;
>>> end;
>>> xmin:=ymin;
>>> xmax:=ymax
>>> end; {findminmax}
>>>
>>> I think this does what the OP asked for.
>>>
>>> Davide
>>>
>>>
>>>
>>>
>>> On May 9, 2013, at 8:19 AM, Camaioni, Donald M wrote:
>>>
>>>> Hi Davide,
>>>>
>>>> It can be programmed via a single command using pro Fit's built in sort routine, e.g., in pro Fit's Pascal programming language:
>>>>
>>>> Sort(window , referenceCol , order , selectionOnly );
>>>>
>>>> Efficiency of this routine has never been an issue for me.
>>>>
>>>> Don
>>>>
>>>> On May 9, 2013, at 7:44 AM, Davide Guarisco wrote:
>>>>
>>>> I would advise against doing that. Sorting is extremely inefficient.
>>>>
>>>> Davide
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On May 8, 2013, at 7:15 AM, Camaioni, Donald M wrote:
>>>>
>>>> I am thinking you would just sort the data and read values from either the resulting first or last row. -Don
>>>>
>>>> On May 8, 2013, at 6:54 AM, Dave wrote:
>>>>
>>>> Hi folks,
>>>>
>>>> While I am anxiously awaiting the Cocoa based, Retina- ready version of pro Fit, a question:
>>>>
>>>> Is there an easy way to find the local minima/ maxima of a set of data or selection of data, and report that point? I mean finding the max or min y value and reporting the x,y coördinate.
>>>>
>>>> Thanks,
>>>> Dave
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>>>>
>>>> ––––––––––––––––––––––––––––––––
>>>> Donald Camaioni, PhD
>>>> Staff Scientist
>>>> Catalysis Science Group
>>>> PHYSICAL SCIENCES DIVISION
>>>>
>>>> Pacific Northwest National Laboratory
>>>> 902 Battelle Boulevard
>>>> P.O. Box 999, MSIN K2-57
>>>> Richland, WA 99352 USA
>>>>
>>>> Tel: (509) 375-2739
>>>> donald.camaioni at pnnl.gov<mailto:donald.camaioni at pnnl.gov>
>>>> www.pnl.gov<http://www.pnl.gov/>
>>>
>>> Davide
>>> --
>>> Davide Guarisco
>>> 5143 Halifax Dr.
>>> San José, CA 95130
>>> Home: (408) 376-0898
>>>
>>>
>>>
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>>
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>
> Davide
> --
> Davide Guarisco
> 5143 Halifax Dr.
> San José, CA 95130
> Home: (408) 376-0898
>
>
>
>
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