ValueWhen X Null values

[andwilson]

Not sure where to post this!

From AB Help

SYNTAX ValueWhen(EXPRESSION, ARRAY, n = 1)
RETURNS ARRAY
FUNCTION Returns the value of the ARRAY when the EXPRESSION was true on the n -th most recent occurrence.
Note: this function allows also 0 and negative values for n - this enables referencing future

It says "Returns the value of the ARRAY when the EXPRESSION was true"
but when array has NULL values, valuewhen will never return NULL value after first time EXPRESSION is true

The code below demonstrate that


Plot( C, "Close", ParamColor("Color", colorBlack ), styleNoTitle | ParamStyle("Style") | GetPriceStyle() );

bi = BarIndex();

XLong = (bi % 200) == 0;
XShort = ((bi+100) % 200) == 0;

Plot(XLong, "XLong", colorGreen, styleHistogram | styleOwnScale);
Plot(XShort, "XShort", colorRed, styleHistogram | styleOwnScale);

// else zero
zLongEntry = IIf(XLong, C, 0);
zShortEntry = IIf(XShort, C, 0);
// else NULL
nLongEntry = IIf(XLong, C, Null);
nShortEntry = IIf(XShort, C, Null);

zL = ValueWhen( zLongEntry > 0 || zShortEntry > 0, zLongEntry);
zS = ValueWhen( zLongEntry > 0 || zShortEntry > 0, zShortEntry);
nL = ValueWhen( !IsNull(nShortEntry) || !IsNull(nLongEntry), nLongEntry);
nS = ValueWhen( !IsNull(nShortEntry) || !IsNull(nLongEntry), nShortEntry);

Plot(nL, "\nnullLong", colorGreen, styleNoLine | styleOwnScale | styleNoLabel);
Plot(nS, "nullShort", colorRed, styleNoLine | styleOwnScale | styleNoLabel);
Plot(zL, "\nzeroLong", colorGreen, styleNoLine | styleOwnScale | styleNoLabel);
Plot(zS, "zeroShort", colorRed, styleNoLine | styleOwnScale | styleNoLabel);

if select bar is placed after a green vertical line (XLong is true) I expect to see

nullShort == NULL and zeroShort == 0

but instead I get

nullShort == (number) and zeroShort == 0

_

Did I miss somethig ?

[andwilson]

[fxshrat]

If you write this

zS = ValueWhen( zShortEntry > 0, zShortEntry);
nS = ValueWhen( !IsNull(nShortEntry), nShortEntry);

Then both return value.



If you write this

zS = ValueWhen( zLongEntry > 0, zShortEntry);
nS = ValueWhen( !IsNull(nLongEntry), nShortEntry);

then 1st one returns zero, 2nd one returns empty.


if you write this
zS = ValueWhen( zLongEntry > 0 OR zShortEntry > 0, zShortEntry);
nS = ValueWhen( !IsNull(nLongEntry) OR !IsNull(nShortEntry), nShortEntry);

Then first returns zero, 2nd one returns value.


If you write this

zS = ValueWhen( zLongEntry > 0 OR zShortEntry > 0, zShortEntry);
nS = ValueWhen( !(IsNull(nLongEntry) OR IsNull(nShortEntry)), nShortEntry);

Then 1st returns zero, 2nd one returns empty.

[fxshrat]

In the third one I actually expect both returning a value since 1st example (short check only) returns value for both (ValueWhen keeps true occurrence). But instead in the third one 1st line returns zero.

I'm a bit puzzled myself.

[andwilson]

Thank you , I complete miss the NOT OR NOT in expression
but still do not get what I expect

[andwilson]

I still does not understand

SetBarsRequired(sbrAll);
Plot( C, "Close", ParamColor("Color", colorBlack ), styleNoTitle | ParamStyle("Style") | GetPriceStyle() );

bi = BarIndex();

XLong = (bi % 100) == 0;
XShort = ((bi+50) % 100) == 0;

Plot(XLong, "XLong", colorGreen, styleHistogram | styleOwnScale);
Plot(XShort, "XShort", colorRed, styleHistogram | styleOwnScale);

// else zero
zLongEntry = IIf(XLong, C, 0);
zShortEntry = IIf(XShort, C, 0);
// else NULL
nLongEntry = IIf(XLong, C, Null);
nShortEntry = IIf(XShort, C, Null);

ncond = (NOT IsNull(nShortEntry)) OR (NOT IsNull(nLongEntry));
zcond = zLongEntry > 0 || zShortEntry > 0;

zL = ValueWhen( zcond, zLongEntry);
zS = ValueWhen( zcond, zShortEntry);
nL = ValueWhen( ncond, nLongEntry);
nS = ValueWhen( ncond, nShortEntry);

Plot(nL, "\nnullLong", colorGreen, styleNoLine | styleOwnScale | styleNoLabel);
Plot(nS, "nullShort", colorRed, styleNoLine | styleOwnScale | styleNoLabel);
Plot(zL, "\nzeroLong", colorGreen, styleNoLine | styleOwnScale | styleNoLabel);
Plot(zS, "zeroShort", colorRed, styleNoLine | styleOwnScale | styleNoLabel);

Plot(ncond, "\nncond", colorGreen, styleNoLine | styleOwnScale | styleNoLabel);
Plot(zcond, "zcond", colorRed, styleNoLine | styleOwnScale | styleNoLabel);



[fxshrat]

Anderson,

I'm puzzled too.
Try AB support.

For this one

zcond = zLongEntry > 0 || zShortEntry > 0;

I actually expected value output larger than zero since it is "OR" and zShortEntry > 0 being true if you apply it alone without the other condition. So I don't understand the zero output if ValueWhen is used.

[fxshrat]

AndWilson, why do you expect Null for nS = ValueWhen( ncond, nShortEntry) ?

The logical link is OR not AND.

Since nS = ValueWhen( !IsNull(nShortEntry), nShortEntry) returns true and nS = ValueWhen( !IsNull(nLongEntry), nShortEntry) returns false
So it is ... = true OR false. So it returns value.


On the other hand the actual result I do not understand is why does

zS = ValueWhen( zLongEntry > 0 OR zShortEntry > 0, zShortEntry) return zero?
Since ValueWhen( zShortEntry > 0, zShortEntry) returns true and as such returns value so the former one (zLongEntry > 0 OR zShortEntry > 0) should return value also since the linking is OR and one condition returning true.

So that's the actual one I do not understand.

[andwilson]

fxshrat

zS = ValueWhen( zLongEntry > 0 OR zShortEntry > 0, zShortEntry) return zero?

returns zero because whenever zLongEntry > 0 , zShortEntry will be zero
and when zShortEntry > 0 , zLongEntry will be zero

[andwilson]

Using NULL values I expected the chart at the bottom, but what I get is the top one, continuous lines

SetBarsRequired(sbrAll);
Plot( C, "Close", ParamColor("Color", colorBlack ), styleNoTitle | ParamStyle("Style") | GetPriceStyle() );

bi = BarIndex();

XLong = (bi % 100) == 0;
XShort = ((bi+50) % 100) == 0;

Plot(XLong, "XLong", colorGreen, styleHistogram | styleOwnScale);
Plot(XShort, "XShort", colorRed, styleHistogram | styleOwnScale);

// else NULL
nLongEntry = IIf(XLong, C, Null);
nShortEntry = IIf(XShort, C, Null);

ncond = NOT (IsNull(nShortEntry) AND IsNull(nLongEntry));

nL = ValueWhen( ncond, nLongEntry);
nS = ValueWhen( ncond, nShortEntry);

Plot(nL, "\nnullLong", colorGreen, styleDashed | styleThick);
Plot(nS, "nullShort", colorRed, styleDashed | styleThick);




SetBarsRequired(sbrAll);
Plot( C, "Close", ParamColor("Color", colorBlack ), styleNoTitle | ParamStyle("Style") | GetPriceStyle() );

bi = BarIndex();

XLong = (bi % 100) == 0;
XShort = ((bi+50) % 100) == 0;

Plot(XLong, "XLong", colorGreen, styleHistogram | styleOwnScale);
Plot(XShort, "XShort", colorRed, styleHistogram | styleOwnScale);

// else zero
zLongEntry = IIf(XLong, C, 0);
zShortEntry = IIf(XShort, C, 0);

zcond = zLongEntry > 0 OR zShortEntry > 0;

zL = ValueWhen( zcond, zLongEntry);
zS = ValueWhen( zcond, zShortEntry);

zL = IIf(zL > 0, zL, Null);
zS = IIf(zS > 0, zS, Null);

Plot(zL, "\nzeroLong", colorGreen, styleDashed | styleThick);
Plot(zS, "zeroShort", colorRed, styleDashed | styleThick);