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Another way of looking at the problem:

When you convert the array to a hash with keys as the array's values, and values as the array's indices, you pay the price for conversion once. Your subsequent lookups will be quite fast. But you do pay for it; the overhead of the hashing algorithm, combined with the O(n) time complexity of converting the entire array to a hash.

On the other hand, if all you're interested in is an occasional search that yields an index, you could use List::MoreUtils first_index function:

use List::MoreUtils 'first_index'; my @array = qw( a b c d e f g h ); my $found_ix = first_index{ $_ eq 'd' } @array; print "Found 'd' at $found_ix.\n"; __END__ output: Found 'd' at 3.

This avoids the one-time overhead of generating hash keys for the entire structure, and the per-search overhead of hash lookups. But now every lookup will be an O(n) operation. If you're doing a lot of lookups this is a net loss. If you're doing few lookups, it could be a win, which would have to be verified via benchmarking.

One nice thing about the first_index method is that its semantics are pretty clear. But if you're doing frequent lookups your original idea of using a hash lookup is good.


Dave


In reply to Re: better array to hash conversion by davido
in thread better array to hash conversion by perltux

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    [davido]: hm, that seems to also survive $< manipulations @corion so good call.
    [Corion]: tye: I also more randomly stumbled over it, as "who am i" unix implementation didn't really provide much help. But Wikipedia linked me to the List of Unix Programs (or something like it), and from there ...
    [talexb]: Wasn't Brexit the name of the first Santana album?
    [tye]: That's funny, saying getlogin() is less secure. For some uses, it is far superior to getpwuid(), precisely for reasons of security.
    [LanX]: search strategy => Perl Functions by Category
    [Corion]: ... I found discussion of the who utility and that it uses the POSIX 2008 getlogin function (but that function was available much earlier and thus even exists in Perl, as a search for getlogin on CPAN brought up Perl 5.26 as first hit
    [tye]: oh, LanX, but I was thinking that it was not a function that Perl provided.
    [Corion]: Yeah, I also went a more roundabout way, just to find that the solution had been with Perl all along! ;)
    [tye]: perhaps the "less secure" comment was motivated by old versions of getlogin() and trolled through the 'last' log trying to match your TTY. On modern Unix, I believe getlogin() just returns a fundamental bit of identity from your process.
    [tye]: (Because every thing you do has that tag available for auditd.)

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