array variables availability in ProRealTime – examples and discussions
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“I’m trying to count the increase of A over time”
The code works, but arrays are special variable that are not related to time (barindex)…
If you want this to work, you will have to use an extra normal variable (related to the barindex/time), for example:$Avg[0]=0
x=x+1 //related to the bar index
$Avg[0]=$Avg[0]+x
Return $Avg[0]1 user thanked author for this post.
Hi JS,
Thanks for that. I’ll get back to you shortly and let you know how i how i go with it. Makes sense but, fingers crossed I can make it work for what I need.
Cheers,
Finning
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I might be missing something since the ‘Array Post’ went down.
When I jump in the $Avg[a] = $Avg[a] + 1 appeared not to work in the same way as b=b+1 for a normal variable.
Also I looked at earlier reference, and though I’m not sure I got what the problem was, I found a problem.
When you used only var in a indicator, you get the variable undefined error message.
Defining it with a value ‘var=0’ everything’s ok.
Now defining it to itself, ‘var = var’ avoids error message and value assigned is automagically set to zero, still ok.
With an array, ‘arr[0] = arr[0]’ doesn’t define the array, but it quietly errors, or stays undefined.
Adding the +1, ‘arr[0] = arr[0]+1 ‘ doesn’t make a difference because the array is still undefined.
I suppose you cannot assign an undefined array to an undefined array or, do arithmetic operations on a undefined array either.
Only solution is to defined the array element with a value before use, by using ‘once’ or checking/setting using ‘isset()’.
Then ‘arr[0] = arr[0]+1 ‘ does work.
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All is ambiguous because normal variables are “set” to be 0 when they are assigned a value all right, but later in the program than where they are used. Example (untested) :
12a = a + 1a = 0So yes, this can be the only two lines in a program and they will just work without error.
It is the craziest thing I have ever seen, especially because PRT does it like this on purpose. The reason is even more spooky : “Otherwise users receive too many error messages and they don’t know what to do”. <– official PRT statement.That example will lead to numerous unpredictable errors – or erroneous situations without you knowing.
With this as the context, you may understand that the way normal variables work is totally wrong; how the array variables work is correct; something which was not assigned a value, should also not be able to be referenced to (use).
This way of working with the normal variables was introduced with V11.1 (or was it v11.0 ?) and the logic behind it – apart from avoiding error messages – seems to be situations like this :
123456789if not PriceSet then // This will not error out because the parser detects that somewhere (down the line !) PriceSet will be assigned a value.[...]endifIf c1 thenPriceSet = 1elsePriceSet = 0endifIt is to be noted that these days even I abuse this way of working, because when a program evolves (gets larger), it becomes more and more difficult to have things in the decent sequence.
Decent Sequence : always first “declare” your variables, and only after that (sequentially in the program) use them.Hence, once you understand this way of working, you can happily abuse it.
Of course it is a bit sad that when people get used to this “bad habit”, they can not understand why array elements (-variables) don’t work this way, and can’t work this way. And please notice : they could when each element is assigned an initial value (like 0, or whatever you want), but with a 1 million elements possible in an array, this is not really efficient usage of memory.You might think that the solution is easy : let PRT just assign a 0 value when it runs into a reference to a variable or array element which was not assigned a value yet. But this is not the general principle with PRT, because this is : [and now look at my first little sample code above] – variable a there *is* assigned a 0 value (on the 2nd line). So I bet you that this a = a + 1 on the first line in that program, leads to just the same “undefined” with unpredictable result. But you won’t run into that because 1. PRT just does not show you the error and 2. a few lines later a is assigned the value of 0 and in the next bar call all is fine. It is only that after two bar calls a will be 1 while you’d expect it to be 2.
Only solution is to defined the array element with a value before use, by using ‘once’ or checking/setting using ‘isset()’.
Saying it like that (kind of out of context) it would imply the same “logic mistake” I made at first in that Arrays topic (currently dead);
Possibly I am wrong again, but what works with normal variables, like123Once counter = 0counter = counter + 1 // Count number of bars processed.can not work with Array elements (not how PRT uses them). Or maybe it does ? Someone might test this :
12345Once a = 17Once $var(a) = 0$var(a) = $var(a) + 1a = a + 1 // Comment out this line and it may still go wrong ?Can we even follow the logic in this ? I can not. This is completely out of control and fails for sure with the a = a + 1 in there.
All right, this means we should not write code like that. Right.
But without the a = a + 1 it still may fail because I don’t think anything in there will later (next call of the bar) know that the a value of 17 was “Once” applied to element 17 of $var. So it will assign 0 to element 17 always, or never, or … or maybe it works. Curious …1 user thanked author for this post.
You threw me a bit with the lack of square bracket in example, got me good for a couple of minutes in editor with warnings before I realised. Just got up. Well done!.
I changed example so ‘a=0’ , just so index didn’t change.
With this example array not defined though ‘a’ is.I see what you mean with example, with ‘a = a + 1’ commented out, ‘a’ and ‘$var[a]’ appear to be both defined.
However, image, I was running, commented out version example in 1hr chart, It appeared to work as expected when it built the chart, incrementing the array by 1 every bar, but as time then moved on, each tick of a 1Tick chart, increased array value, not each bar.
Placing the, ‘a = a +1’ prior to array appears to work as expected with the incrementing by 1 of the array.
This appears to mean, apart from weird, that there’s a state where the array is defined and holds values independent of the normal bar end.
Say, to define, normal bar values is barState, this other state appears to be tickState, where the tick is of a 1tick chart tick.
One other thing I noticed is that, if you only use ‘once a = 17’ in a file on its own with return a, it appears defined.
Adding in, ‘once $var[a] = 0, appears to define the array.
Adding in, ‘$var[a] = $var[a] + 1’ seems to be in this barState when chart building, and then, tickState when continuing.
Adding in, ‘a = a + 1’ after array, just undefines the array, and ‘a’ continues as expected.1 user thanked author for this post.
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