Odd wave indexing behavior

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Tue, 02/14/2017 - 11:53 am

Hi all,

Here's some simple code that feels like it should work, but doesn't, and I'm wondering what's going on. I'm trying to populate a 2x6 matrix with two pre-existing 1x6 waves. I've tried this in multiple ways, and it never works the way I expect it to.

The following properly inserts wave0 into the first row of Matrix and wave1 into the second row.
Function ConcatenateWaves()
Variable Number=CountObjects("",1)
wave wave0
wave wave1
Wavestats/Q wave0
Variable Length=v_npnts
Make/O/N=(Number,Length) Matrix
Matrix[0]=wave0[q]
Matrix[1]=wave1[q]
End


If I try to automate that so I don't have to predefine wave0 and wave1 (there will ultimately be many more of these waves), strange things occur.
Function ConcatenateWaves()
Variable Number=CountObjects("",1)
Wave wave0
Wavestats/Q wave0
Variable Length=v_npnts
Make/O/N=(Number,Length) Matrix
Variable ni=0
String Name
    Do
    Name=GetIndexedObjName("",1,ni)
    Wave w=$Name
    Matrix[ni]=w[q]
    ni+=1
    While(ni<Number)
End

Here, I'm referencing wave0 and wave1 through GetIndexedObjName. When I do it this way, only the first column of Matrix populates - all other columns are zero. WaveRefIndexed behaves similarly. Clearly I'm missing something here, probably something obvious. What is it?
Well, how about this:
Function ConcatenateWaves(WAVE col0, WAVE col1)

    Make/O/N=(2,numpnts(col0)) Matrix
    Matrix[0][] = col0[q]
    Matrix[1][] = col1[q]
End

You need the empty brackets on the left side; then you can use q on the right.

But really, you want the Concatenate operation.

John Weeks
WaveMetrics, Inc.
support@wavemetrics.com

February 14, 2017 at 12:20 pm - Permalink

First, you're making the wave Matrix which then gets counted within "GetIndexedObjName" and messes up your loop.

Second, your second function wouldn't even compile for me in Igor 7. You have to be a bit more explicit in your wave assignment; use Matrix[ni][]=w[q]:
Function ConcatenateWaves()
Variable Number=CountObjects("",1)
String WavesToConcatenate=WaveList("*",";","") //new
Wave wave0
Wavestats/Q wave0
Variable Length=v_npnts
Make/O/N=(Number,Length) Matrix
Variable ni=0
String Name
    Do
    Name=StringFromList(ni,WavesToConcatenate) //new
    print name
    Wave w=$Name
    Matrix[ni][]=w[q] //new
    ni+=1
    While(ni<Number)
End

Last, you might explore MatrixOp or Concatenate as alternative ways to do what you want.

February 14, 2017 at 12:27 pm - Permalink

johnweeks wrote:
Well, how about this:
Function ConcatenateWaves(WAVE col0, WAVE col1)

    Make/O/N=(2,numpnts(col0)) Matrix
    Matrix[0][] = col0[q]
    Matrix[1][] = col1[q]
End

You need the empty brackets on the left side; then you can use q on the right.

But really, you want the Concatenate operation.

John Weeks
WaveMetrics, Inc.
support@wavemetrics.com


Thanks John. That fixes it. I tried Concatenate and ended up w/ a 1x12 rather than a 2x6 - probably had syntax problems there as well.

February 14, 2017 at 12:46 pm - Permalink

Concatenate/O/NP=1 {wave0,wave1}, Matrix forces appending columns, but without /NP flag it should just promote correctly if the waves are the same length.

February 14, 2017 at 02:02 pm - Permalink