Rails - Jan 2008 - nice way to split an array into 3 equally sized pieces

before i start writing my own sophisticated small algorithm i thought i
ask you guys how to do this in a rails way ..

given array:
a = [1, 2, 3, 4, 5, 6, 7]

out of this array i need an array b holding three elements where each of
them holds the same size of elements ... if not possible then the last
one should hold less .. so for the above it would be

b = [[1, 2, 3], [4, 5, 6], [7]]

another example:
a = [1, 2] => b = [[1], [2], []]

thanks for the simplest way
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On 7 Jan 2008, at 13:18, Michal Gabrukiewicz wrote:
>
> before i start writing my own sophisticated small algorithm i  
> thought i
> ask you guys how to do this in a rails way ..
>
> given array:
> a = [1, 2, 3, 4, 5, 6, 7]
>
> out of this array i need an array b holding three elements where  
> each of
> them holds the same size of elements ... if not possible then the last
> one should hold less .. so for the above it would be
>
> b = [[1, 2, 3], [4, 5, 6], [7]]
>
> another example:
> a = [1, 2] => b = [[1], [2], []]
>
Well not massively nice but

def split(array)
   length = (array.length / 3.0).ceil
   [array[0, length], array[length, 2*length], array[2*length,  
3*length]]
end


Fred

On Jan 7, 2008, at 7:18 AM, Michal Gabrukiewicz wrote:
>
> before i start writing my own sophisticated small algorithm i  
> thought i
> ask you guys how to do this in a rails way ..
>
> given array:
> a = [1, 2, 3, 4, 5, 6, 7]
>
> out of this array i need an array b holding three elements where  
> each of
> them holds the same size of elements ... if not possible then the last
> one should hold less .. so for the above it would be
>
> b = [[1, 2, 3], [4, 5, 6], [7]]
>
> another example:
> a = [1, 2] => b = [[1], [2], []]
>
> thanks for the simplest way
>
in_groups_of

a = [1,2,3,4,5,6,7]

a.in_groups_of(3)

[[1,2,3], [4,5,6], [7,nil,nil]]

or

a.in_groups_of(3, false)

[[1,2,3], [4,5,6], [7]]

Peace,
Phillip


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Phillip Koebbe wrote:
> On Jan 7, 2008, at 7:18 AM, Michal Gabrukiewicz wrote:
> 
>> them holds the same size of elements ... if not possible then the last
>> one should hold less .. so for the above it would be
>>
>> b = [[1, 2, 3], [4, 5, 6], [7]]
>>
>> another example:
>> a = [1, 2] => b = [[1], [2], []]
>>
>> thanks for the simplest way
>>
> 
> in_groups_of
> 
thanks philip but this does it exactly the other way round .. fred''s 
version is fine but it was a bit buggy .. this works fine

  #splits an array into 3 equal parts
  def split_array(array)
    length = (array.length / 3.0).ceil
    [array[0, length], array[length, length], array[2 * length, length]]
  end
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Michal Gabrukiewicz wrote:
> thanks philip but this does it exactly the other way round ..
fred''s
> version is fine but it was a bit buggy .. this works fine
> 
>   #splits an array into 3 equal parts
>   def split_array(array)
>     length = (array.length / 3.0).ceil
>     [array[0, length], array[length, length], array[2 * length, length]]
>   end
You know, if I had been paying attention, I would have done two things 
differently:

1) ran your second example
2) noticed that Fred did *not* suggest in_groups_of

Either one of those would have been sufficient to tell me that my idea 
was not correct.

<crawling back into his cave>

Peace,
Phillip
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On 7 Jan 2008, at 15:42, Michal Gabrukiewicz wrote:
>
> Phillip Koebbe wrote:
>> On Jan 7, 2008, at 7:18 AM, Michal Gabrukiewicz wrote:
>>
>>> them holds the same size of elements ... if not possible then the  
>>> last
>>> one should hold less .. so for the above it would be
>>>
>>> b = [[1, 2, 3], [4, 5, 6], [7]]
>>>
>>> another example:
>>> a = [1, 2] => b = [[1], [2], []]
>>>
>>> thanks for the simplest way
>>>
>>
>> in_groups_of
>>
>
> thanks philip but this does it exactly the other way round ..
fred''s
> version is fine but it was a bit buggy .. this works fine
>
>  #splits an array into 3 equal parts
>  def split_array(array)
>    length = (array.length / 3.0).ceil
>    [array[0, length], array[length, length], array[2 * length,  
> length]]
>  end
Oops, I obviously went on crack when I typed it into my mail client :-)

Fred


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>> [1, 2, 3, 4, 5, 6, 7].in_groups(3)
=> [[1, 2, 3], [4, 5, nil], [6, 7, nil]]

Note that the in_groups takes 1 from each of the last 2 columns instead 
of 2 from the last.
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2009/10/3 Morgan Christiansson
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>:
>
>>> [1, 2, 3, 4, 5, 6, 7].in_groups(3)
> => [[1, 2, 3], [4, 5, nil], [6, 7, nil]]
>
> Note that the in_groups takes 1 from each of the last 2 columns instead
> of 2 from the last.
That is as documented, you want in_groups_of

Colin