Am 09.05.2020 um 13:59 schrieb Costello, Roger L. costello(_at_)mitre(_dot_)org:
Hi Folks,
I need a super-efficient way to compute the sum of A[i] * B[i] for i=1 to n.
For example, suppose A is this:
<row>
<col>0.9</col>
<col>0.3</col>
</row>
and B is this:
<row>
<col>0.2</col>
<col>0.8</col>
</row>
I want to compute:
(0.9 * 0.2) + (0.3 * 0.8)
Here's one way to do it:
sum(for $i in 1 to count($A/col) return number($A/col[$i]) * number($B/col[$i]))
I suspect that is not the most efficient approach.
What is the most efficient approach? I will be doing hundreds of thousands of
these computations, so I want to use the most efficient approach.
You can express it a bit more nicely in XPath 3 with higher-order
functions as
sum(for-each-pair($A/col, $B/col, function($a, $b) { $a * $b}))
but whether that performs better or worse is something you can only measure.
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