From: Robert Klemme <bob.news@...>
Date: 2004-12-14T05:37:18+09:00
Subject: Re: [Nuby] Sorting a Hash and keepint it as a Hash?

>
> "Williams, Chris" <Chris.Williams@xeroxlabs.com> schrieb im Newsbeitrag 
> news:A0AC2703C633EB48B5DFEF66D6EBF7120E49DD@wcxlms02.wcrt.xeroxlabs.com...
> Another nuby question:
>
> I have a Hash of objects which I want to sort by the values. Afterwards
> I want to pull out the keys as one array and the values as another. So I
> have code like so:

You want sort with a block:

>> h={1=>"a",2=>"b"}
=> {1=>"a", 2=>"b"}
>> h.sort {|(k1,v1),(k2,v2)| v1 <=> v2}
=> [[1, "a"], [2, "b"]]

If you use inject you can get your two arrays in one go:

>> h.sort {|(k1,v1),(k2,v2)| v1 <=> v2}.inject([[],[]]) {|(ks,vs),(k,v)| ks 
>> << k; vs << v; [ks,vs]}
=> [[1, 2], ["a", "b"]]
>> keys, values = h.sort {|(k1,v1),(k2,v2)| v1 <=> v2}.inject([[],[]]) 
>> {|(ks,vs),(k,v)| ks << k; vs << v; [ks,vs]}
=> [[1, 2], ["a", "b"]]
>> keys
=> [1, 2]
>> values
=> ["a", "b"]

> # sort by frequency ascending
> @fault_sums = @fault_sums.sort {|a,b| a[1] <=> b[1]}
> # Only keep top N
> @fault_sums.slice!(0...-@number) if @number <= @fault_sums.size
>
> fields = @fault_sums.keys
> data = @fault_sums.values
>
> But when I get to calling keys and values on the Hash I realized, sort
> actually returns back a 2D array and those methods aren't defined on an
> Array. Is there a way to make the 2D Array returned by the sort back
> into a Hash?

This won't help as the hash you get then is unsorted again.  If you need a 
copy, Hash#dup or Marshal.load(Marshal.dump(hash)) is a better choice.

Kind regards

    robert