Quick channel group history clear?

[kedi]

Have channel group T. Want to clear the history of the whole group. Is there a one step command? Or do I need to loop?

[AzeoTech]

You would need a loop.  Use channel.listall() to get a list of all the channels in the group, then loop through them, using execute() to call clearHistory() on each one.

[kedi]

private string clist = channel.listAll("T1")
for (private i = 0, i < numrows(clist), i++)
   execute("ClearHistory" + clist + )
endfor

This throws an error.

C1070 Not enough parameters for the given operator: Discharge Line 3 - Uncaught error in sequence Discharge

I missed something here. Is is because it is a channel group? I need to use a different command parameter?

[AzeoTech]

When using execute() or evaluate() and things don't go as planned, I recommend adding a ? statement before it so you can see what the string you are building becomes.  In your case, you have to fix a more fundamental error first, the trailing + sign.  Then it would read:

? "ClearHistory" + clist
execute("ClearHistory" + clist)

The next problem is that clist is an array, and you aren't subsetting.  Since string concatenation with + only supports scalars, DAQFactory will ignore the array and just use the first element ([0]).  Well, that isn't what you want.   You need to add after clist to get each channel in the list as you iterate.

Finally, once you fix all the syntax errors:

? "ClearHistory" + clist
execute("ClearHistory" + clist)

You'll see that the string you are building makes no sense.  ClearHistory is a function of individual channels.  So, to clear the history of myChannel you would do:

myChannel.clearHistory()

In your case, if clist has "myChannel", you'd get:

ClearHistoryMyChannel

which will do nothing but probably generate another error.  The ? statement would show you this problem.  So, you need to modify your string build up to create the correct string.