Re: Array or Hash

At doing what?

Both scale the same for insertions (amortised O(1)).
Both scale the same for fetches (amortised O(1)).
A fetch should take a little longer with a hash, but I suspect this wouldn't be the deciding factor in most cases.
You can really only delete from the start and from the end of an array — anything else can be expensive since it requires shifting the elements — but deleting from a hash should be cheap. For tiny hashes or arrays, this shouldn't be significant.
You can really only insert at the start and the end of an array — anything else can be expensive since it requires shifting the elements — but inserting into a hash should be cheap. For tiny hashes or arrays, this shouldn't be significant.

In short, I doubt you'll notice a difference.

Comment on Re: Array or Hash

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Re^2: Array or Hash by BrowserUk (Patriarch) on Jan 21, 2011 at 17:26 UTC
Both scale the same for insertions (amortised O(1)) Care to demonstrate how insertions into an array amortise to O(1)? Both scale the same for fetches (amortised O(1)). A fetch should take a little longer with a hash, but I suspect this wouldn't be the deciding factor in most cases. You wouldn't notice if your programs ran 5 times slower? `perl -MTime::HiRes=time -E"@a=1..1e6;$t=time; ++$a[$_] for 1..1e6; printf qq[%f\n], time()-$t" 0.146912 perl -MTime::HiRes=time -E"%h=map{($_)x2}1..1e6;$t=time; ++$h{$_} for 1..1e6; printf qq[%f\n], + time()-$t" 0.525000` [download] Or an order of magnitude more slowly? `perl -MTime::HiRes=time -E"$t=time;my @a; $a[$_]=1 for 1..1e6; printf qq[%f\n], time()-$t" 0.220181 perl -MTime::HiRes=time -E"$t=time;my %h; $h{$_}=1 for 1..1e6; printf qq[%f\n], time()-$t" 1.805000` [download] Concealing reality behind grand sounding theoretical BS is all the worse as you obviously know better. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l] [select]
Re^3: Array or Hash by ikegami (Patriarch) on Jan 21, 2011 at 18:35 UTC
Care to demonstrate how insertions into an array amortise to O(1)? Oops, that's limited to insertions at the start or end. Concealing reality behind grand sounding theoretical BS is all the worse as you obviously know better. You have it backwards. I avoided the theoretical BS, sticking to real world cases. You wouldn't notice if your programs ran 5 times slower? Some yes, some no, but what's that got to do with my comment? You didn't demonstrate any correlation between data structure access time and run time of my programs, much less 1:1. as you obviously know better. Enough with the lies and personal attacks.	[reply]
Re^4: Array or Hash by BrowserUk (Patriarch) on Jan 21, 2011 at 18:51 UTC
Oops, that's limited to insertions at the start or end. Still wrong: `C:\test>perl -MTime::HiRes=time -E"$t=time; my @a; push @a, 1 for 1 .. 219; say (time()-$t)/219" 0.123739004135132 C:\test>perl -MTime::HiRes=time -E"$t=time; my @a; push @a, 1 for 1 .. 220; say (time()-$t)/220" 0.226538896560669 C:\test>perl -MTime::HiRes=time -E"$t=time; my @a; push @a, 1 for 1 .. 221; say (time()-$t)/221" 0.46043586730957` [download] I avoided the theoretical BS, sticking to real world cases. You get worse. 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.	[reply] [d/l]
Re^5: Array or Hash by ikegami (Patriarch) on Jan 21, 2011 at 19:24 UTC
Re^6: Array or Hash by BrowserUk (Patriarch) on Jan 21, 2011 at 19:41 UTC
Re^6: Array or Hash by BrowserUk (Patriarch) on Jan 21, 2011 at 22:02 UTC