Variable history?

[kedi]

When I created a component to display a variable value, it initially displayed a whole row of the values of that variable incremented as in the sequence code. When specified MyVariable(0) in the component expression window, instead of just MyVariable, I then got just one, current instance of the variable value. Does every variable have a history generated? Can I force it to not have a history in the declaration of the variable?

I ask in relation to the wimpy little laptop that the code is running on. Less overhead would be nice.

[AzeoTech]

First, the correct syntax is MyVariable[0] and this is required if MyVariable is an array, otherwise the variable value control will display the first 20 values.  Variables won't generate history on their own if you use = to give them values.  So:

global x
x = 3
x = 2

does not generate an array with {2,3}.  It creates a variable called x, assigns 3 to it, then assigns 2 to it, overwriting the 3.  To create a history with a variable you have to use myVariable.addValue() on it.  That said, a history is just an array, and there are other ways you can make a variable an array, such as myVariable.append(), etc, along with direct assignment of a specified array (i.e. x = {3,2}), and direct setting of array elements (i.e. x[3] = 2). 

 

And of course if you do myVariable = myChannel and myChannel has a history, then myVariable will have a copy of that history.  A useful thing when you want to capture the current history before new data appears.  It works for subsets too:

myVariable = myChannel[0,99]

or

myVariable = myChannel[systime(), systime() - 60]