Editing Topic: RCR245 Project: RCR | RCRchive home

RCR 245: zip's broken metaphor

submitted by neoneye on Wed Apr 14 2004 03:19:56 AM -0700

Status: pending

Abstract

Enumerable#zip is good at making pairs. In a way that is intuitive and easy to grasp.

#zip is taking a block. Guess what happens.

(1..4).zip(1..4) {|a,b| a*b }

Problem

The problem is that nothing happens, the zip returns nil. It shows up that zip is commonly being used for multiway each! Thats a broken metaphor, which give people bad habits. See [] for discussion.

Proposal

I propose that zip concatenates and returns the result of the supplied block.

(4..6).zip(10..12) {|a,b| a*b } #=> [40, 55, 72]
%w(a b c).zip(1..9) {|i| i.reverse } #=> [[1, 'a'], [2, 'b'], [3, 'c']]

Analysis

incompatibility for people which has used zip for multiway each. However they should use callcc/enumerator instead of this bad habbit.

Implementation

don't know what to write.

----
David Black:

I'm not sure about all this 'bad habit' and 'broken' stuff, but I do find it odd that #zip returns nil with a block.

Just for fun, here's an implementation:

<pre>

module Z
    def Z.included(c)
      c.class_eval {
        alias oldzip zip
        def zip(*others,&block)
          if block
            res = []
            newblock = Proc.new { |*args| res << block.call(*args) }
            oldzip(*others,&newblock)
            return res
          else
            oldzip(*others)
          end
        end
        }
    end
  end

class Array; include Z; end
class Range; include Z; end
  
  # and perhaps track down every Enumerable and do likewise....

</pre>

(BTW, your 'reverse' example doesn't need the square brackets around i.reverse.  Each element will already be an array.)
----
Fixed the <code>reverse</code> example. Thanks David.

I made another implementation (didn't use each). Buts thats
not of interest <b>[</b><a href="http://ruby-talk.org/97006">rubytalk:97006</a><b>]</b>. 
Lacks time to do a nice implementation with enumerator/callcc.. maybe when 
I get really tired I do that ;-)

BTW: I cannot seem to get links working inside this RCR comment.

-- Simon Strandgaard

----

Just looked at the source code and I think your proposal would lead to unnecessary array creation in case you don't need one.

If you need an Array, you can type 4 letters extra:  a.zip(b).map {...} => [...]

It's the same like #each returning self.

Although I'm not a native speaker, I don't think, zip is semantically demanding an array
as return value.

Could you explain, how enumerator can be used, I have no idea ?

-- Matthias Georgi
----
enumerator can be used to convert from one type of each to another.
continuations can be used to restart the program. Together they can
be used for multiway each.

I have made an iterator class, which is useful for multiway each.
See <a href="http://aeditor.rubyforge.org/iterator/">homepage</a>.

<pre>require 'iterator'
data_a = %w(a b c d)
data_b = (0..3)
ia = Iterator::Continuation.new(data_a, :each)
ib = Iterator::Continuation.new(data_b, :each)
result = []
while ia.has_next? and ib.has_next?
    result << ia.current
    result << ib.current
    ia.next
    ib.next
end
ia.close
ib.close
p result   # ["a", 0, "b", 1, "c", 2, "d", 3]</pre>

----

OK, looks like Generator, SyncEnumerator from stdlib.
But I would only use them to pass Iterators around or to avoid recursion in combination with a stack.
For general use it's too javalike, i was so confident not to type these "while next?" thing anymore.
So probably it's personal taste, for me it's a good habit to write

I use this very often and Iteration based on Continuation is also not very performant.

-- Matthias Georgi
----
Yes its java like.. it was just an example of how multiway each, over a one zillion
of elements could be accomplished. People with such needs, should probably use
C rather than using zip for this. Such demands is very specialized.
I think zip rather should be targeted for the most common usage.

Have you ever felt wanting to supply a block to zip itself?

BTW: How do you convince a Perl girl to use Ruby, if you have to explain to her, 
that zip, is not zip in that paticular case, and you have to do a map afterwards!

-- Simon Strandgaard

----

OK, i see the inconsistency.
I'm not sure, what i expect from zip.
open() for example returns also different values, with and without a block.

-- Matthias Georgi
----
Great ;-)

Usually <code>open</code> is some kind of factory method, and factories can build many kinds of products. <code>zip</code> is not really in that category.

For instance <code>map</code> returns the same as if you had
supplied a simple block. The same would be nice with <code>zip</code>.

<pre>server&gt; irb
irb(main):001:0&gt;  a = %w(a b c)
=&gt; ["a", "b", "c"]
irb(main):002:0&gt; a.map
=&gt; ["a", "b", "c"]
irb(main):003:0&gt; a.map{|i| i}
=&gt; ["a", "b", "c"]
irb(main):004:0&gt; a.zip
=&gt; [ ["a"], ["b"], ["c"] ]
irb(main):005:0&gt; a.zip{|i| i}
=&gt; nil        ## [ ["a"], ["b"], ["c"] ] is what this RCR is about.
irb(main):006:0&gt;</pre>

The last line is what this RCR is about.

-- Simon Strandgaard

=== Add comments here

----

Back to RCRchive.

RCR Submission page and RCRchive powered by Ruby, Apache, RuWiki (modified), and RubLog