Convert array to array-of-arrays?

ruby-talk
1

have a look at enum.partition (http://ruby-doc.org/core/classes/
Enumerable.html#M003161)

cheers

···

On Feb 4, 10:45 am, Phlip <phlip2...@gmail.com> wrote:

Rubies:

Given [1, 2, 3, 4], what's the most Rubiesque way to get [[1, 2], [3, 4]]?

I had figured a variation on Array#transpose would be available, but I can't
find one!

--
   Phlip

2

Not sure what the OP wants, but AFAIK #partition only ever returns two
partitions. If the task is to combine consecutive elements
#each_slice works well:

$ irb -r enumerator
irb(main):001:0> [1, 2, 3, 4].to_enum(:each_slice, 2).to_a
=> [[1, 2], [3, 4]]
irb(main):002:0>

Kind regards

robert

···

2008/2/4, Chris Hulan <chris.hulan@gmail.com>:

On Feb 4, 10:45 am, Phlip <phlip2...@gmail.com> wrote:

> Given [1, 2, 3, 4], what's the most Rubiesque way to get [[1, 2], [3, 4]]?
>
> I had figured a variation on Array#transpose would be available, but I can't
> find one!

have a look at enum.partition (http://ruby-doc.org/core/classes/
Enumerable.html#M003161)

--
use.inject do |as, often| as.you_can - without end

3

Chris Hulan wrote:
>> Given [1, 2, 3, 4], what's the most Rubiesque way to get [[1, 2], [3, 4]]?
> have a look at enum.partition (http://ruby-doc.org/core/classes/
> Enumerable.html#M003161)

I can't partition by value, so the closest conceptual match would be something like:

assert do
   \[1, 2, 3, 7\]\.partition\_with\_index\{|p,i| i\.odd? \}\.transpose ==
        \[\[1, 2\], \[3, 7\]\]
end

And that's a heckuva lot of typing, even if partition_with_index existed!

--
Phlip

Roll your own?

class Array
  def regroup(count)
    # do some Ruby awesomeness*
  end
end

a = [1, 2, 3, 4]

[1, 2, 3, 4]

a.regroup(2)

[[1, 2], [3, 4]]

* - exercise left up to the reader

···

On Feb 4, 10:00 am, Phlip <phlip2...@gmail.com> wrote:

4

Have a look at Facets.Enumerable.group_by (http://facets.rubyforge.org/
quick/rdoc/core/classes/Enumerable.html#M000423)
Lots of other neat stuff there...

Cheers

···

On Feb 4, 11:00 am, Phlip <phlip2...@gmail.com> wrote:

Chris Hulan wrote:
>> Given [1, 2, 3, 4], what's the most Rubiesque way to get [[1, 2], [3, 4]]?
> have a look at enum.partition (http://ruby-doc.org/core/classes/
> Enumerable.html#M003161)

I can't partition by value, so the closest conceptual match would be something like:

    assert do
       [1, 2, 3, 7].partition_with_index{|p,i| i.odd? }.transpose ==
            [[1, 2], [3, 7]]
    end

And that's a heckuva lot of typing, even if partition_with_index existed!

--
   Phlip

5

Ruby-docs.org indicates Object.to_enum exists in latest 1.8.6, can you
upgrade?

···

On Feb 4, 11:32 am, Phlip <phlip2...@gmail.com> wrote:

Robert Klemme wrote:
> irb(main):001:0> [1, 2, 3, 4].to_enum(:each_slice, 2).to_a

Thanks! Now, for those of us mired in the doldrums of Ruby 1.8.x, how to write
to_enum in Ruby? I found each_slice, and I know C and ruby.h, but my Ruby
internals are rusty...

--
   Phlip

6

AFAIK it is in *all* Ruby 1.8.* versions. You just need an extra "require" (see my first posting in this thread).

Cheers

  robert

···

On 04.02.2008 17:32, Phlip wrote:

Robert Klemme wrote:

irb(main):001:0> [1, 2, 3, 4].to_enum(:each_slice, 2).to_a

Thanks! Now, for those of us mired in the doldrums of Ruby 1.8.x, how to write to_enum in Ruby? I found each_slice, and I know C and ruby.h, but my Ruby internals are rusty...

7

"Excessive moduli"?

irb(main):003:0> %w{foo bar}.each_with_index {|e,i| puts "key #{e}" if i % 2 == 0}
key foo
=> ["foo", "bar"]
irb(main):004:0> %w{foo bar}.each_with_index {|e,i| puts "key #{e}" if i & 1 == 0}
key foo
=> ["foo", "bar"]

Cheers

  robert

···

On 04.02.2008 17:46, Phlip wrote:

The winner is ActiveSupport's Array#in_groups_of (calling each_slice).

Thanks y'all!

But it only won for one reason - I need the array-of-twos so I can then immediately call .each on it. in_groups_of already requires a block (and does not return the twizzled array!), so I can just use it without the each. So I would have called it each_group, but that didn't seem to catch on...

Here's why I need it. Ruby's opcodes express Hashes as strictly even-lengthed arrays, going [key1, value1, key2, value2, etc]. So I just needed to iterate those things in pairs, without excessive moduli to detect if the current item is a key or a value.

8

PS: In case you wondered: it's pretty easy:

$ irb
irb(main):001:0> EnumProxy = Struct.new :obj, :args do
irb(main):002:1* include Enumerable
irb(main):003:1> def each(&b)
irb(main):004:2> obj.send(*args,&b)
irb(main):005:2> self
irb(main):006:2> end
irb(main):007:1> end
=> EnumProxy
irb(main):008:0> class Object
irb(main):009:1> def to_enum(*a)
irb(main):010:2> EnumProxy.new self, a
irb(main):011:2> end
irb(main):012:1> end
=> nil
irb(main):013:0> %w{foo bar}.to_enum(:each_with_index).each {|*a| p a}
["foo", 0]
["bar", 1]
=> #<struct EnumProxy obj=["foo", "bar"], args=[:each_with_index]>
irb(main):014:0> %w{foo bar}.to_enum(:each_with_index).find {|a,b| b==1}
=> ["bar", 1]

Kind regards

  robert

···

On 04.02.2008 19:22, Robert Klemme wrote:

On 04.02.2008 17:32, Phlip wrote:

Robert Klemme wrote:

irb(main):001:0> [1, 2, 3, 4].to_enum(:each_slice, 2).to_a

Thanks! Now, for those of us mired in the doldrums of Ruby 1.8.x, how to write to_enum in Ruby? I found each_slice, and I know C and ruby.h, but my Ruby internals are rusty...