From: seebs@... (Peter Seebach)
Date: 2007-05-04T02:00:11+09:00
Subject: Re: Array to Hash

In message <20070503164957.06CAC41A5C@guild.seebs.net>, Peter Seebach writes:
>In message <463a10df$0$27400$ba4acef3@news.orange.fr>, Josselin writes:
>>is it possible to convert easily an Array like this one :
>>[ nil, "b", nil, nil, nil , "f", "g", nil, nil, "j"]
>>to an Hash like this one
>>{ 1 => "b", 5 => "f", 6 => "g", 9 => "j"  }
>>where the key is the position of  a value if not nil .. ?

>Yes.

I thought about this more.  I'd like to explain WHY there's no code
in the above:

Because this is not just easy, but bloody obvious.  What do you want
to do?  You want to, for each index in the array, record its value
in a hash if it has a value.  (Congrats!  You've just reinvented sparse
arrays!  Please put your hand in the cookie jar to see whether there's
a cookie.)

So, what do you need?  You need to do something for each index in the
array.  If ONLY the Array class provided an each_index method... Oh, but
it does.

So, given an index, can you imagine a way to write code to extract the
member of an array at that index?  You'd need some kind of operator to
extract a member of an array.  And a way to check whether a value is nil.
All of these are not merely available, but easy.  Even if you don't
know that there's an each_index method, it's not hard to maintain a count
and do 'count = count + 1; b[count] = x' or something similar.

I guess this strikes me as a question that would have benefitted a lot from
some explanation of why you weren't just looking at the Array documentation
and trying a few things.

-s