assigning a variable through an if elseif statement

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Mon, 10/17/2016 - 02:18 pm

I'll start to say that I'm new to Igor but this forum has helped me to an amazing amount of stuff so far, but I've run into something I'm not sure how to handle. I have a wave (harmonic) that consists of ~7000 entries of value 1, ~7000 of value 3, etc. to value 11. I'd like to split this wave into several waves by value 1, 3, 5, 7, 9, and 11. The difficult part is that the original wave may not have all values present. I'm using the following code to do this where I search the wave for transitions from one value to another and assign that point as the variable (end1st) that I'll use later to duplicate just the portion of the original wave I want. Here's the code I'm using:

    Make seq1st3rd={1,3,3},seq1st5th={1,5,5},seq1st7th={1,7,7},seq1st9th={1,9,9},seq1st11th={1,11,11}//Waves to find end of 1st harmonic
    FindSequence /V=seq1st3rd Harmonic
    Variable/G/C trans1st3rd=V_Value
    FindSequence /V=seq1st5th Harmonic
    Variable/G/C trans1st5th=V_Value
    FindSequence /V=seq1st7th Harmonic
    Variable/G/C trans1st7th=V_Value
    FindSequence /V=seq1st9th Harmonic
    Variable/G/C trans1st9th=V_Value
    FindSequence /V=seq1st11th Harmonic
    Variable/G/C trans1st11th=V_Value
    if (trans1st3rd!=-1)
        Variable/G/C end1st=trans1st3rd
    elseif (trans1st5th!=-1)
        Variable/G/C end1st=trans1st5th
    elseif (trans1st7th!=-1)
        Variable/G/C end1st=trans1st7th
    elseif (trans1st9th!=-1)
        Variable/G/C end1st=trans1st9th
    elseif (trans1st11th!=-1)
        Variable/G/C end1st=trans1st11th
    else
        Variable/G end1st=DimSize(Harmonic,0)
    endif


This code compiles fine if I omit the last portion:

    else
        Variable/G end1st=DimSize(Harmonic,0)


That part is there to basically say if you don't find any transitions from value 1 to another value, then the original wave must only have values of 1, so just assign the variable end1st to whatever the dimension size of that wave is. Without this last piece, the procedure won't work for waves that only have values of 1. The error that I get is that it says that the variable end1st already exists. So I'm confused as to why all the previous elseif statements work properly (no variable seems to be assigned unless one of the if statements is true) but I get the compile error when I try to use that last bit. Not sure if it matters but I've also tried the following to replace the last else statement but have the same problem with the variable already being in use.

elseif (trans1st3rd==-1)&&(trans1st5th==-1)&&(trans1st7th==-1)&&(trans1st9th==-1)&&(trans1st11th==-1)
        Variable/G end1st=DimSize(Harmonic,0)


Thanks in advance for any help!
There's a couple simpler ways to get to your goal instead of fussing around with FindSequence indexes and Duplicate. Here I'll presume you're trying to pull out the 5's.

You might be happy with the Extract command, which doesn't preserve the original wave dimension but at least counts the number of values for you?
Extract Harmonic, HarmonicFives, Harmonic==5

The /INDX flag may also be useful so that you know where those occurred in the original sequence.

The command "SelectNumber" could also work...for example:
Duplicate Harmonic HarmonicFives
HarmonicFives=SelectNumber(Harmonic[p]==5,NaN,Harmonic[p])

This will result in a wave filled with 5's where the original wave had 5's but NaN everywhere else.

Another option is MatrixOp with the "equal" command, but it fills the output wave non-matching values with 0's instead of NaN's in the above example, and its output wave type may not be what you need.
MatrixOP HarmonicFives = 5*equal(Harmonic,5)


If you need to reduce the size of the waves output (e.g. to get rid of the 0's or NaN's), you could follow up with a Sort and Redimension.

October 17, 2016 at 03:34 pm - Permalink

Just some comments regarding the problem of variable declaration:
- First, I don't know why you use the /C flag (complex variable), as the output is clearly not complex. Ist there some reason to use complex values later in the procedure?
- Also, there is no /C flag on your last statement, which should rather give you an "inconsistent type" compile error. Maybe you use an older Igor version ... (which one?)
- I would recommend to avoid using global variables in general until you are really really sure you need them. Just declare a normal variable once and assign the values in your if statement (you could also first assign a normal variable and then save the result in a global variable in a separate step later if needed).
Hope that helps a bit with future coding endeavors.

October 17, 2016 at 11:06 pm - Permalink

Thanks ajleenheer! The extract function with /INDX flag was exactly what I needed, it works perfectly for this. And to chozo, I originally thought I would have complex numbers in some data, but I definitely wouldn't have here so I wouldn't need the flag. As for the /G flag, I understand why it's better to not use that now. I had a couple procedure windows open where I would test parts of the code, so adding the /G flag helped with that but from what I've read since your comment sounds like that's not very good practice.

October 18, 2016 at 06:45 am - Permalink

You may streamline the code also with either of these approaches ...

do
    FindSequence/V=seq1st3rd Harmonic
    if (V_value!=-1)
        end1ist = v_value
        break
    endif
    FindSequence/V=seq1st5th Harmonic
    if (V_value!=-1)
        end1st = v_value
        break
    endif
    ...
while(1)


OR

make/N=3/FREE seqwave
for (ic=0;ic<5;ic+=1)
    seqwave = seqmatrix[ic][p]
    FindSequence/V=seqwave Harmonic
    if (v_value!=-1)
        end1ist = v_value
        break
    endif
endfor


The first uses the seq waves as you have. The second collapses the seq waves in to a matrix (that you have to set up) and then iterates using the matrix.

Caveat: These still have to be tested (they are "off the top of my head" if you will).

--
J. J. Weimer
Chemistry / Chemical & Materials Engineering, UAH

October 18, 2016 at 09:58 am - Permalink

For good practices of global variables you may want to take a look here: http://www.igorexchange.com/node/7118
To debug your code you rather should use the build-in debugger, which gives you insight into the values of variables while the function is running (and all kinds of other information) instead of just the last (global) value after everything is done. Execute the following line in the Igor command window to learn more about the debugger:
DisplayHelpTopic "The Debugger"

October 19, 2016 at 09:19 pm - Permalink