How do I access a specific value from a wave and take this one to appear in the legend?

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I have a probably really easy-to-answer question, but I couldn't find an answer by myself (hard to get good keywords so a search gives the desired answer).

I have series of data files where one is varied as a function of the other and a second one is kept fixed fro one measurement (one file). This second parameter varies only from one file to the next. All three values are written in a tab-separated text-file

eg.
A B C
-3.151500E-9 -2.574253E-8 -1.000000E-1
-2.913400E-9 -2.241544E-8 -1.000000E-1
-2.703300E-9 -1.972218E-8 -1.000000E-1

So I measure B with respect to A, and C is the same for this file but will be different for the next file.

In the graph I want now to have the value of C to appear as the legend. So fare I tried to define the wave accordingly by naming the string strIsd accordingly 
sprintf strIsd "V\Bg\M =%.0W1PV"+strIsd ,wave2[0]

I don't know if this is the right way to access a number of a wave. But my procedure seemed to work fine first, but now I get an error in the line 
 	duplicate /O wave1, $strIsd
saying "expected wave name".
So I suppose my way of doing it is already not so nice and it then works only in some cases.
I don't see any specific differences in the files which would indicate any reason that the error occurs on these files but not on other.

Thanks for any help



macro loadVsd_varied()
	string /G path 
	string /G head

	variable	num
	string	fname
	string	strVg
	string	strIsd
	string	strVsd
	string 	nummer
	variable 	strlength
	
	display 
	LoadWave/G/D/W/A/C
	fname=RemoveEnding(S_fileName,".txt")
	strlength = strlen(fname)
	num=str2num(fname[strlength-4,strlength])
	head=fname[0,strlength-5]
	path=S_path


	do
		sprintf  nummer "%*.*d" 1, 4, num
		fname = path + head + nummer + ".txt"

		strVg = "wv"+head+"Vg" + nummer
		strIleak = "wv"+head+"Ileak" + nummer
		strVsd = "wv"+head+"Vsd" + nummer

		strIsd = " "+head+ nummer
		sprintf strIsd "V\Bg\M =%.0W1PV"+strIsd ,wave2[0]

		duplicate /O wave0, $strVg
		duplicate /O wave1, $strIsd
		duplicate /O wave2, $strVsd
		killwaves wave0, wave1, wave2
			
		append $strIsd vs $strVg

		num += 1

		LoadWave/G/D/W/A/C fname
	while(V_flag>0)
	Legend
end
It came to my mind that the name just became too long. Does somebody know what the maximum allowed length is?

August 17, 2010 at 07:00 am - Permalink
tatj wrote: It came to my mind that the name just became too long. Does somebody know what the maximum allowed length is?

Wave names, as well as other Igor object names, can be up to 31 characters in length. But I think your problem is (also?) that your wave name contains characters such as a space and equals sign that require you to use liberal names, and to use liberal names you have to enclose the name in single quotes.

Execute the following commands on Igor's command line for more information:

DisplayHelpTopic "Liberal Object Names"
DisplayHelpTopic "Programming with Liberal Names"


Your life will be much easier if you refrain from ever using liberal wave and object names if that's possible.

August 17, 2010 at 09:17 am - Permalink
The maximum length of a name is 31 characters.

Keep in mind that the error sometimes occurs in the line preceding the line that is highlighted when Igor reports the error.

By writing macros instead of functions, you are limiting what you can do in Igor programming, limiting execution speed, and not benefitting from compile-time checking of syntax. You can't use structures, switch statements, pass-by-reference parameters, for loops, free waves, data folder references and many other features. Also, all new features will be added to functions so the list of what you can not use will grow. So I recommend that you use functions instead of macros. Below is your macro rewritten as a function with comments indicating what I changed.

Also, it is better to pass parameters to a procedure rather than relying on global variables. I would pass the pre-existing waves (wave0, wave1, wave2) as parameters and also the strleak string variable which appears to be a global string variable. Or perhaps strleak does not need to be a global at all and should be a local variable.

To learn about functions, execute:

DisplayHelpTopic "User-Defined Functions"




Function loadVsd_varied()
	string /G path 
	string /G head
 
	variable	num
	string	fname
	string	strVg
	string	strIsd
	string	strVsd
	string 	nummer
	variable 	strlength
 
	display 
	LoadWave/G/D/W/A/C
	fname=RemoveEnding(S_fileName,".txt")
	strlength = strlen(fname)
	num=str2num(fname[strlength-4,strlength])
	head=fname[0,strlength-5]
	path=S_path
 
 	Wave wave0, wave1, wave2		// *** Added this - declare waves
 	
	do
		sprintf  nummer "%*.*d" 1, 4, num
		fname = path + head + nummer + ".txt"
 
		strVg = "wv"+head+"Vg" + nummer
		
		SVAR strIleak	// *** Added this - declare global string variable
		strIleak = "wv"+head+"Ileak" + nummer
		
		strVsd = "wv"+head+"Vsd" + nummer
 
		strIsd = " "+head+ nummer
		sprintf strIsd "V\Bg\M =%.0W1PV"+strIsd ,wave2[0]
 
		duplicate /O wave0, $strVg
		duplicate /O wave1, $strIsd
		duplicate /O wave2, $strVsd
		killwaves wave0, wave1, wave2
 
		AppendToGraph $strIsd vs $strVg	// *** Changed append to AppendToGraph
 
		num += 1
 
		LoadWave/G/D/W/A/C fname
	while(V_flag>0)
	Legend
end

August 17, 2010 at 09:21 am - Permalink
Thanks for the answers.
Would there also be another/easier way to define the legend, then by using the wave names?

August 18, 2010 at 12:14 am - Permalink
hrodstein wrote:
By writing macros instead of functions, you are limiting what you can do in Igor programming, limiting execution speed, and not benefitting from compile-time checking of syntax.


What is then the actual difference between macros and functions? If you say I would better use functions, what are then macros for?

August 24, 2010 at 01:05 am - Permalink
tatj wrote:
hrodstein wrote:
By writing macros instead of functions, you are limiting what you can do in Igor programming, limiting execution speed, and not benefitting from compile-time checking of syntax.


What is then the actual difference between macros and functions? If you say I would better use functions, what are then macros for?

Execute 
DisplayHelpTopic "Comparing Macros And Functions"
in Igor to bring up the documentation that details the differences. There is a bullet list in that topic. The summary is that in almost every way, functions are superior to macros. Therefore, unless you require a macro (such as a window recreation macro), write the code as a function instead.

Macros existed before functions, so for backwards compatibility they still exist.

August 24, 2010 at 08:34 am - Permalink