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Re^2: Array vs. Hash for sparsely integer-indexed data

by BrowserUk (Pope)
on Jan 25, 2013 at 21:48 UTC ( #1015415=note: print w/ replies, xml ) Need Help??

in reply to Re: Array vs. Hash for sparsely integer-indexed data
in thread Array vs. Hash for sparsely integer-indexed data

Also not to be excluded entirely is ... uhh ... an array of integers that is searched sequentially each time.

That is a surprise winner for my 'Worst Advice of the Month (January, 2013)' prize.

... set up a few short test-runs ...

I'd suggest you take your own advice before doling it out to others.

NB: The following uses 1/10 the number of values and 1/10 the number of lookups than the tests above for arrays, hashes and bit vectors, because it takes so long to complete.:

@a = map $_*20, 1 .. 1e4;; say total_size \@a;; 320176 $found=0; say time; for my $tgt ( 1 .. 20e4 ) { $tgt == $_ and ++$foun +d and last for @a; }; say time; say $found;; 1359149323.02034 1359149541.80419 10000

Using that as the basis for estimation, the total size will be 3.2MB -- 12 times that required by the bitvector solution.

And the lookups that took hashes 1 second; arrays 2/5ths of a second and bitvectors 1/3rd of a second; would take: 25 days!

It is really hard to see any circumstance when this would be a viable solution.

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

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