[rules-users] pattern binding and eval()

[Wolfgang Laun]

With those four accumulates to compute the four sums I wouldn't worry
about the eval.

If there are many Position facts in WM and they are all A1 or A2 or B1
or B2 and you want an efficient solution: consider a single-pass
accumulate with custom code to compute the sums, returning a boolean.

-W


On 19 December 2011 11:00, Harris <harrisx at gmx.de> wrote:
> Hi,
>
> I have a question regarding pattern binding and eval().
>
> The following rule calculates 4 different sums from a list of
> "Positions" and determines whether the ratio of the first 2 sums
> is smaller than the ratio of the latter 2 sums.
>
> The first version reads quite intuitively but it uses
> eval() which - as far as I gather from the docs - should
> be avoided whenever possible.
>
> The second version doesn't use eval() since it binds to a
> patten, namely the "Number" that represents the sum A1. But the
> relation cannot be seen as clearly as in version1.
>
> Is there another, more elegant way to write this rule which I miss?
> And does the use of eval() in this case come with any perfomance
> or other drawbacks?
>
> Thanks for your help!
>
> Harris
>
>
> # ---------------------
> rule "Test-version1"
>  when
>
>  Number( $sumA1: doubleValue ) from accumulate( Position( posType == "A1",
> $val : value ),  sum( $val ) )
>  Number( $sumA2: doubleValue ) from accumulate( Position( posType == "A2",
> $val : value ),  sum( $val ) )
>  Number( $sumB1: doubleValue ) from accumulate( Position( posType == "B1",
> $val : value ),  sum( $val ) )
>  Number( $sumB2: doubleValue ) from accumulate( Position( posType == "B2",
> $val : value ),  sum( $val ) )
>
>  eval ( ($sumA1 / $sumA2) <  ($sumB1 / $sumB2));
>
>  then
>
>  System.out.println("Ratio A smaller than ratio B !");
>
> end
> # ---------------------
> rule "Test-version2"
>  when
>
>  Number( $sumA2: doubleValue ) from accumulate( Position( posType == "A2",
> $val : value ),  sum( $val ) )
>  Number( $sumB1: doubleValue ) from accumulate( Position( posType == "B1",
> $val : value ),  sum( $val ) )
>  Number( $sumB2: doubleValue ) from accumulate( Position( posType == "B2",
> $val : value ),  sum( $val ) )
>  Number( doubleValue  < (($sumB1/$sumB2)* $sumA2) ) from accumulate(
> Position( posType == "A1", $val : value ),  sum( $val ) )
>
>  then
>
>  System.out.println("Ratio A smaller than ratio B !");
>
> end
> # ---------------------
>
> --
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