One can calculate the standard deviation with just one pass over the data set by iterating once over the numbers, calculating both the sum and the sum of squares in one go.

In the case of only 7 numbers to sum over that doesn't make much of a difference (0.57s vs. 0.48s on my machine), The difference becomes more pronounced when there are more numbers in one set, when the whole array doesn't fit into the cache anymore (2.94s vs. 4.04s for 1k lists with 7k items each).

But when such micro optimizations become important, it's worth pointing out that writing things in C (via XS or Inline::C) might be much faster.

Perl 6 - links to (nearly) everything that is Perl 6.

In reply to Re^2: Poor performances with threads by moritz
in thread Poor performances with threads by olafmar

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