From: Phrogz <phrogz@...>
Date: 2007-12-19T11:50:01+09:00
Subject: Re: Hash#collate

On Dec 18, 6:29 pm, Trans <transf...@gmail.com> wrote:
> On Dec 18, 7:05 pm, Phrogz <phr...@mac.com> wrote:
>
> > I wanted a method like Hash#update, but that preserved the values from
> > both the original and argument Hash. A little searching failed to find
> > it. (I did find that someone somewhere wrote a Hash#collate that's in
> > my ri docs, but who knows where it came from. Its description appears
> > not to do at all what I wanted, anyhow.)
>
> That's from Facets, probably. But the latest version of Facets renamed
> it to #mash, for "map hash", which is more descriptive of what it
> does. (#collate remains an alias for the time being).
>
> I like your definition --actually I'm surprised I haven't worked this
> functionality into Facets yet. I guess I thought #weave took care of
> it, but that's slightly different b/c it only combines arrays if the
> value is already an array. So I'm going to add this to Facets. A
> couple thoughts though...
>
> The options don't feel quite right. Maybe it would more versatile to
> define #uniq on Hash? So then
>
>   { :a=>1, :b=>2 }.collate( { :a=>1, :b=>3 } ).uniq
>   #=> { :a=>[1], :b=>[2,3] }

That's an excellent point. I needed this functionality today and so I
included it in the script; however, since it's a simple one-line (as
seen in the implementation) post-process step, perhaps it's
appropriate to keep it out of this method.


> As for preserving the arrays, I'm not sure. Is that really all that
> useful? Well, if it is it seems like a better definition for Hash#zip.

The reason I made the arrays not be preserved by default is to enable
chained collation of 3 or more hashes. (test5_multicollate in the unit
tests.) I was actually collating hundreds today. However, I put in the
'preserve arrays' because it seemed almost arbitrary to treat them
differently from every other type of value. I don't personally have a
use case that needs it now, but I know from experience (like #flatten
versus #flatten_once) how sometimes arrays of arrays can suddenly crop
up and need to be preserved.

I would dearly love to get rid of the options hash altogether,
though. :)