Masking data points for display

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Thu, 10/14/2010 - 05:16 pm

I am finding it hard to understand the logic behind the syntax of the mask command in Igor. Virtually 100% of references on the web to using the mask functionality in Igor are in regards to masking for curve fitting purposes. I want to mask the display of data points. I have waves with dummy values so that the number of points match x waves. I do not want these dummy values displayed. I do not understand this syntax:

modifygraph mask(wavename)={maskwavename,0,0}

where maskwavename is 0 for masked points and 1 for unmasked. Can anyone explain the logic here? Why can't I just say use this maskwavename for this wavename? What is the purpose of those zeroes? One I could understand, but two is beyond me. I think this is something that could be better explained in the help reference, i.e. an example would be incredibly useful.
You can achieve some very sophisticated effects with the rather complicated command in Igor. For instance, you might have a mask wave with numbers that correspond to different researchers, and you can use the various modes and values to select subsets of the different researchers. The problem with such sophistication is that it makes it harder to use in simple cases!

In the use you describe, another way to go would be to use wave subranges. If you have a Y wave that has fewer points than the X wave, you can add it to a graph with a command like this:
AppendToGraph shortYWave vs longXWave[0, numpnts(shortYWave)-1]

If you don't have a graph yet, you can use "Display" instead of "AppendToGraph".

This doesn't require padding the Y wave as you describe. If you have other reasons for adding the extra points to the Y wave, you can apply a subrange to both X and Y:
AppendToGraph paddedYWave[0, lastGoodPoint] vs longXWave[0, lastGoodPoint]


John Weeks
WaveMetrics, Inc.
support@wavemetrics.com

October 15, 2010 at 11:59 am - Permalink