Ton, Rob -
Not exactly.
Last post on this, I promise, but the details can be important in other
situations where AFL cannot make this transparent.
Ton, let's expand your example slightly -
// This is an array ...
myString = Close;
_TRACE("myString1 "+myString);
_TRACE("myString2 "+Ref(myString,-1));
_TRACE("myString3 "+Ref(myString,-2));
// This still is an array ...
mySuperStr = StrToNum(NumToStr(Close));
_TRACE("mySuperString1 "+ ( mss = mySuperStr) );
_TRACE("mySuperString2 "+ ( mss1 = Ref(mySuperStr,-1)) );
_TRACE("mySuperString3 "+ ( mss2 = Ref(mySuperStr,-2)) );
_TRACE( "TYPES - " + typeof( mss ) + " , " +
typeof( mss2 ) + " , " +
typeof( mss2 ) );
Buy = Sell = Short = Cover = 0;
All that I've done is made it a Scan and assigned three variables ( mss, mss1,
mss2) to the values that you are tracing. Note that the output in debug that
I've added is -
TYPES - number , array , array
The variable mySuperStr is a SCALAR NUMBER. What happens when you reference
previous values is that it is PROMOTED to an array of ALL THE SAME VALUE (the
last range value of Close). So, mss1 and mss2 are arrays.
This promotion is probably what seems confusing. It is NOT that AFL recognizes
all the same value and treats it as a scalar. It is that AFL recognizes when
it wants an array, and promotes a scalar to an array.
Rob, if you want to prove this, consider the following -
test = C - C + 5;
parm = Param( "parm", test, 1, 10, 1 );
Buy = Sell = Short = Cover = 0;
In this case, the variable "test" is an array of all 5's. You can't use it in
the Param() statement where it wants a scalar for the default value.
Hope that this explains it fully.
-- Bruce
P.S. BTW, one example of why this distinction is important relates to the CBT.
When you run a normal AFL, it makes a syntax pass and can detect where
parameter types are not correct - as in the Param() example above. If there is
a type problem in the CBT, it doesn't show an error. This is because the CBT
code is usually wrapped in a statement like -
if ( status( "actionex" ) == actionportfolio )
{...}
So, they syntax checking pass can't "get into" that code block to do checking.
--- In [email protected], "Rob" <sidharth...@...> wrote:
>
> Ton,
>
> As I have alluded to several times, AFL can spot an array with the same value
> all the way through it and in such a case can treat it like a scalar... which
> is what it does here.
>
> Think about it... if an array has exactly the same value all the way through,
> and you know it, why would you give an error when accessing the array as a
> scalar...?? You'd have to be very pedantic. Luckily AFL isn't so pedantic!
>
> --- In [email protected], "Ton Sieverding" <ton.sieverding@> wrote:
> >
> > Hi Bruce,
> >
> > What I did is the following :
> > // This is an array ...
> >
> > myString = Close;
> >
> > _TRACE("myString1 "+myString);
> >
> > _TRACE("myString2 "+Ref(myString,-1));
> >
> > _TRACE("myString3 "+Ref(myString,-2));
> >
> > // This still is an array ...
> >
> > mySuperStr = StrToNum(NumToStr(Close));
> >
> > _TRACE("mySuperString1 "+mySuperStr);
> >
> > _TRACE("mySuperString2 "+Ref(mySuperStr,-1));
> >
> > _TRACE("mySuperString3 "+Ref(mySuperStr,-2));
> >
> > Putting Close in myString makes myString an array. Therefore I can access
> > all the historical elements in myString. Now we do the String Trick. This
> > gives me mySuperString. The fact that all elements are the same does not
> > mean that mySuperString no longer is an array. mySuperString is an array
> > because I can access all elements ...
> >
> >
> >
> > So my question is, mySuperString being an array, how than is it possible
> > that I can handle this array with a simple IF. Why doesn't AmiBroker give
> > me an error ? Saying that I should use the complex IIF ...
> >
> > Regards, Ton.
> >
> >
> >
> > ----- Original Message -----
> >
> > From: Bruce
> > To: [email protected]
> > Sent: Monday, June 14, 2010 2:29 PM
> > Subject: [amibroker] Re: impenetrable AFL
> >
> >
> >
> > Yuki, Ton,
> >
> > Let me make what is hopefully a constructive suggestion.
> >
> > When in doubt, use AddColumn() for debug. It is your friend. In this
> > case, you might do something like the following Explore -
> >
> > res = StrToNum( NumToStr( C ) );
> > Filter = BarIndex( ) >= BarCount - 10;
> > AddColumn( C, "C", 8.2 );
> > AddColumn( res, "RES", 8.2 );
> > Plot( C, "C", colorred );
> > Title = "" + NumtoStr( C );
> >
> > Here's what happens in the code above. NumtoStr(C) must result in a
> > single string. So, in an Explore it takes the last Range value and converts
> > it to a string. (An indicator is a little different.) Then, the StrtoNum
> > just converts it back to a single scalar number. The easiest way to see
> > this is to "print it out" via AddColumn() statements.
> >
> > The promotion that Rob alluded to is a little different. It is when a
> > single scalar number of "promoted" to an array to carry out a calculation.
> > Consider the following -
> >
> > fact = 1.1;
> > array = Close * fact;
> >
> > The second statement multiples an array (Close) by a scalar number
> > (fact). There are a couple of ways to do this internally, but the easiest
> > way to visualize it is that fact is "promoted" to an array of numbers with
> > a value of 1.1 , and then the two arrays are multiplied.
> >
> > Hope this helps.
> >
> > -- Bruce
> >
> > --- In [email protected], "Rob" <sidhartha70@> wrote:
> > >
> > > It doesn't give you the same array... it gives you a scalar.
> > > (as Bruce mentioned it seems sometimes AFL can see an array has the
> > same value all the way through and treats it as a scalar).
> > >
> > > --- In [email protected], Yuki Taga <yukitaga@> wrote:
> > > >
> > > > That was exactly my take on it. Wonderful that I can use IF, but why
> > > > is it possible?
> > > >
> > > > Tomasz ???? (The layman's interpretation, please.) ^_^
> > > >
> > > > Yuki
> > > >
> > > > Monday, June 14, 2010, 5:11:34 PM, you wrote:
> > > >
> > > > TS> Rick changing a string to a number THAT'S COMING FROM AN ARRAY
> > > > TS> and after that changing a number to a string again, should give
> > > > TS> me the same array with the initial strings. But the fact that I
> > > > TS> can use IF after the string manipulation shows me that I am no
> > > > TS> longer having an array ... I still do not get this. Weird ...
> > > >
> > > > TS> Tomasz ????
> > > >
> > > > TS> Regards, Ton.
> > > >
> > > >
> > > > TS> ----- Original Message -----
> > > > TS> From: Rick Osborn
> > > > TS> To: [email protected]
> > > > TS> Sent: Sunday, June 13, 2010 5:33 PM
> > > > TS> Subject: Re: [amibroker] impenetrable AFL
> > > >
> > > >
> > > > TS>
> > > >
> > > > TS> First off let me repeat - this is not my original code.
> > > > TS> I found it in someone's code for TD Sequential (with apologies
> > > > TS> to the original coder - didn't keep your name)
> > > >
> > > > TS> The Buysignal is a Flip(Buy,Sell) type - or could be a true/false
> > item.
> > > >
> > > > TS> Checking the help file the NunToStr says
> > > > TS> FUNCTION It is used to convert numeric value of NUMBER or ARRAY
> > to string.
> > > > TS> Next the StrToNum function
> > > > TS> FUNCTION It is used to convert numeric value of NUMBER or ARRAY
> > to string.
> > > > TS> So the combination of changing that value of the array from a
> > > > TS> number to a string and then "that string" back to "a number" (not
> > an array)
> > > >
> > > > TS> LastValue works the same but I still don't understand that
> > function well enough.
> > > > TS> From the help file
> > > > TS> FUNCTION Returns last calculated value of the specified
> > > > TS> ARRAY. The result of this function can be used in place of a
> > > > TS> constant (NUMBER) in any function argument.
> > > > TS> If ARRAY is undefined (e.g., only 100-days loaded and
> > > > TS> you request the last value of a 200-day moving average) then the
> > > > TS> lastvalue function returns zero.
> > > > TS> Caveat: since this function fills an entire data array
> > > > TS> with the last value of another array, it allows a formula to look
> > into the future.
> > > > TS> so if there are repeated events (buy signals and sell
> > > > TS> signals), I'm not sure if lastvalue sees any but the last one.
> > Plus I worry about the Caveat!!
> > > >
> > > >
> > > > TS> Best Regards
> > > > TS> Rick Osborn
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > TS> ----------------------------------------------------------
> > > > TS> From: Ton Sieverding <ton.sieverding@>
> > > > TS> To: [email protected]
> > > > TS> Sent: Sun, June 13, 2010 2:55:32 AM
> > > > TS> Subject: Re: [amibroker] impenetrable AFL
> > > >
> > > > TS>
> > > > TS> 
> > > >
> > > > TS> That's interesting code, Rick. Can you explain me why this works ?
> > > >
> > > > TS> 1. First I assume BuySignal to be BUY. Therefore being an
> > > > TS> array. So IF should not work. Should be IIF. But even when I put
> > > > TS> there BUY to be sure it's an array, it does work. Why ?
> > > >
> > > > TS> 2. What's the difference between StrToNum(NumtoStr( BUY)) and
> > > > TS> BUY ? Should give me the same result. But is does not. Without
> > > > TS> this trick I cannot use IF. What's going on here ????
> > > >
> > > > TS> Regards, Ton.
> > > >
> > > >
> > > > TS> ----- Original Message -----
> > > > TS> From: Rick Osborn
> > > > TS> To: amibro...@yahoogrou ps.com
> > > > TS> Sent: Saturday, June 12, 2010 10:52 PM
> > > > TS> Subject: Re: [amibroker] impenetrable AFL
> > > >
> > > >
> > > > TS>
> > > >
> > > > TS> Yuki
> > > >
> > > > TS> I have the following code which changes the background
> > > > TS> gradient color depending on whether a buy or sell signal is given.
> > > >
> > > > TS> if(StrToNum(NumToStr(BuySignal)) )
> > > > TS> bgColor = ColorRGB(0,66, 2);
> > > > TS> else
> > > > TS> bgColor = ColorRGB(66,2, 0);
> > > > TS> SetChartBkGradientF ill( colorBlack, bgColor);
> > > >
> > > >
> > > > TS> Perhaps you can change this to meet your needs
> > > >
> > > >
> > > > TS> Best Regards
> > > > TS> Rick Osborn
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > TS> ----------------------------------------------------------
> > > > TS> From: Yuki Taga <yukit...@tkh. att.ne.jp>
> > > > TS> To: amibro...@yahoogrou ps.com
> > > > TS> Sent: Sat, June 12, 2010 1:24:58 AM
> > > > TS> Subject: [amibroker] impenetrable AFL
> > > >
> > > > TS>
> > > > TS> Impenetrable! (At least to me.)
> > > >
> > > > TS> xcolor = IIf(TSI >= SigLine, SetChartBkGradientF ill(
> > > > TS> ParamColor(" BgTop", ColorRGB( 172,172,172 )),
> > > > TS> ParamColor(" BgBottom" , ColorRGB( 172,172,172 ))),
> > > > TS> SetChartBkGradientF ill( ParamColor(" BgTop", ColorRGB(140,
> > 140,140)) ,
> > > > TS> ParamColor(" BgBottom" , ColorRGB(140, 140,140)) ));
> > > >
> > > > TS> SetChartBkColor( SelectedValue( xcolor));
> > > >
> > > > TS> I tried that line above as
> > > > TS> SetChartBkGradientF ill(SelectedValu e(xcolor) ); but that
> > produced a
> > > > TS> syntax error.
> > > >
> > > > TS> I think you can see what I'm trying to do here. The idea is
> > simple:
> > > > TS> change the background gradient depending on a true/false result.
> > The
> > > > TS> gradients in this example are not the gradients I would actually
> > use
> > > > TS> (in fact they are not gradients at all, as your intelligent eyes
> > will
> > > > TS> quickly have seen). They are just test code to see if I can even
> > > > TS> make it work. I cannot.
> > > >
> > > > TS> For one thing, the gradient does not change no matter the selected
> > > > TS> value. It's static. For another thing, the margin background goes
> > > > TS> to black, a hideous (although somewhat foreseen) result.
> > > >
> > > > TS> Okay, what am I doing wrong, and where did I miss this in the
> > docs?
> > > > TS> And what, if anything, can I do about this margin result? The only
> > > > TS> way I can change the *entire* background color is by not using a
> > > > TS> gradient??? (Using SetChartBkColor) How sad that would be! I can
> > > > TS> make that work, at least. But not with a gradient.
> > > >
> > > > TS> Anything is possible in Amibroker, right?
> > > >
> > > > TS> Wrong?
> > > >
> > > > TS> Thanks,
> > > >
> > > > TS> Yuki
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > TS>
> > > >
> > >
> >
>
