Re: Old Timers ??

["J.D. Smith" <jdsmith(at)astro.cornell.edu>]

Paul van Delst wrote:
> O.k., following the advice that "he who asks a question is a fool for 5 minutes, he who
> does not ask a question is a fool forever" I have to ask:
> 
> What is a hash?
> 
> I have seen the term used before regarding string searches but, being a mostly fortran
> number crunchy type programmer, I've never been one for searching through strings and what
> not.

Also known as a "named associative list", or "associative array", hashes
(or "hash tables") are specialized lookup tables.  You can think of them
as arrays indexed, not with numeric indices, but with string values (or
even other data types for some languages).  In the example in this
thread, a hash element would exist for each keyword... e.g.

hash["file ID"]="test"
hash["otherkeyword"]=12.22

etc.  Hashes are like infinitely malleable structures, which is why they
are so nice.  They are somewhat complicated to make (not for us, but for
the language designers), but easy and fast to use.  Here's a link I
found:  http://www.math.utah.edu/~beebe/software/hash/hash.html.

Hashes are built into Perl, which is why they are so popular these days,
I think (no offense to the lisp programmers out there).

JD

 
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