Make plot with markers using every 10th point?

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Sat, 05/30/2015 - 03:08 pm

I have a set of data in which the data are very closely spaced, I think something like 1000 data points. I was wondering if it's possible to plot the data using markers (so I don't have to use colors or dashed lines) but only use every 10th or 15th or 20th point. Is that possible without simply making a new wave? How do I do it?
Hi,

Put the graph into Lines and markers mode and then in modify trace dialog, sparse markers will be an option.

mskip=n Puts a marker on only every nth data point in lines and markers mode (mode=4). Useful for displaying many data points when you want to identify the traces with markers. The maximum value for n is 32767.

If you want to do it in other modes then I think you have to do it manually by creating a new wave.

May 30, 2015 at 03:30 pm - Permalink

That works! I just set the line width to 0 and now it looks like I want!

Oh it IS in the GUI, it's called "sparse markers" I just hadn't tried "Lines and Markers" because I didn't want the line!

May 30, 2015 at 03:32 pm - Permalink

Also have a look at
displayhelptopic "Subrange Display Syntax"

which allows to plot less but evenly spaced data points from a function / the command line.
Make /N=2000 Data=p
Display Data[0,2000;100]
ModifyGraph mode=3

HJ

May 31, 2015 at 02:10 am - Permalink

A great thing about Igor (and this forum for highlighting it) is there are often many ways to do one thing... so I'm always learning. My approach to this is to use a Macro (not written by me) to decimate a wave. It makes a copy, which is not what the OP wants to do, but I thought I'd post this as it might be useful to somebody.
Macro ReduceErrorBars (sourceName, factor)
    String sourceName
    Prompt sourceName, "Source Wave", popup WaveList("*", ";", "")
    Variable factor=10, n=1, count=1, npoints
    Prompt factor, "Keep every nth point"

    npoints=numpnts($sourceName)
    PauseUpdate; Silent 1

    Do
    If (count!=n*factor)
    $sourceName[count]=nan
    else
    n+=1
    endif
    count+=1
    while (count<=npoints)
End

p.s. the name ReduceErrorBars is a bit misleading. It means reduce the number of points (not the size). It's useful for error waves.

May 31, 2015 at 11:49 am - Permalink