From: Nathan Broadbent <nathan.f77@...>
Date: 2012-11-11T18:42:17+09:00
Subject: [ruby-core:49218] Re: [ruby-trunk - Feature #7241] Enumerable#to_h proposal

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>
> Clojure has a function (({into})) that might fit the bill.
>>
>
> This indeed looks very promising.


I like the sound of 'into', but am not sure about appending results with
the '<<' operator. If Hash had '<<' and '+' aliases for 'update' and
'merge' (respectively), we might as well give 'map' an optional argument,
and call:

    [1,2,3].map({}) {|i| { i => i ** 2 } }

And if Hash#update accepted a two-element array, we could do:

    [1,2,3].map({}) {|i| [i, i ** 2] }

So I like the 'into' name, but I think it would be more useful as an alias
for 'each_with_object', instead of just 'map' with an argument for the base
object.



> I often want a "collect" method where I'm not forced to collect exactly
> one item per item of the original collection. If collect weren't an alias
> to map, I think it would even make a lot of sense to use the word "collect"
> for this (map: one-to-one, collect: one-to-many).
>

Ruby has a 'flat_map' method (aliased as 'collect_concat') that flattens
the first level of a returned array, so you can append multiple results,
and don't need to use compact. See
http://ruby-doc.org/core-1.9.3/Enumerable.html#method-i-flat_map

    [1,nil,2].flat_map {|i| i ? [i] : [] }    #=> [1, 2]


Best,
Nathan

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<div class=3D"gmail_quote"><blockquote class=3D"gmail_quote" style=3D"margi=
n:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class=3D"im"=
><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1=
px #ccc solid;padding-left:1ex">

Clojure has a function (({into})) that might fit the bill.<br>
</blockquote>
<br></div>
This indeed looks very promising.</blockquote><div><br></div><div>I like th=
e sound of &#39;into&#39;, but am not sure about appending results with the=
 &#39;&lt;&lt;&#39; operator. If Hash had &#39;&lt;&lt;&#39; and &#39;+&#39=
;=A0aliases for=A0&#39;update&#39; and &#39;merge&#39; (respectively), we m=
ight as well give &#39;map&#39; an optional argument, and call:</div>

<div><br></div><div>=A0 =A0 [1,2,3].map({}) {|i|=A0{ i =3D&gt; i ** 2 } }</=
div><div><br></div><div>And if Hash#update accepted a two-element array, we=
 could do:</div><div><br></div><div>=A0 =A0 [1,2,3].map({}) {|i| [i, i ** 2=
] }</div>

<div><br></div><div>So I like the &#39;into&#39; name, but I think it would=
 be more useful as an alias for &#39;each_with_object&#39;, instead of just=
 &#39;map&#39; with an argument for the base object.</div><div><br></div>

<div><div>=A0</div></div><blockquote class=3D"gmail_quote" style=3D"margin:=
0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
I often want a &quot;collect&quot; method where I&#39;m not forced to colle=
ct exactly one item per item of the original collection. If collect weren&#=
39;t an alias to map, I think it would even make a lot of sense to use the =
word &quot;collect&quot; for this (map: one-to-one, collect: one-to-many).<=
br>

</blockquote><div><br></div><div>Ruby has a &#39;flat_map&#39; method (alia=
sed as &#39;collect_concat&#39;) that flattens the first level of a returne=
d array, so you can append multiple results, and don&#39;t need to use comp=
act. See=A0<a href=3D"http://ruby-doc.org/core-1.9.3/Enumerable.html#method=
-i-flat_map">http://ruby-doc.org/core-1.9.3/Enumerable.html#method-i-flat_m=
ap</a></div>

<div><br></div><div>=A0 =A0 [1,nil,2].flat_map {|i| i ? [i] : [] } =A0 =A0#=
=3D&gt; [1, 2]</div><div><br></div><div><br></div><div>Best,<br>Nathan</div=
></div>

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