From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2013-06-18T05:47:53+09:00
Subject: Re: Compare and sort one array according to another.

On Mon, Jun 17, 2013 at 9:56 PM, masta Blasta <lists@ruby-forum.com> wrote:
> Joel Pearson wrote in post #1112686:
>> masta Blasta wrote in post #1112677:
>>> Joel Pearson wrote in post #1112665:
>>>> If the items within each array belong to each other, how about a
>>>> multidimensional array?
>>>>
>>>> arr = [
>>>> [ Obj1(prop1, prop2, id), OthrObj1(prop1, prop2, ref_id) ],
>>>> [ Obj2(prop1, prop2, id), OthrObj2(prop1, prop2, ref_id) ],
>>>> [ Obj3(prop1, prop2, id), OthrObj3(prop1, prop2, ref_id) ]
>>>> ]
>>>>
>>>>
>>>> All the sorting is dealt with together then:
>>>>
>>>> sorted_arr = arr.sort_by { |obj1, obj2| obj1.id }
>>>
>>> I don't quite understand everything that's happening here. Can you
>>> elaborate a bit more on your solution.
>>
>> I'm going by your comment here:
>> "The objects in arr2 have a 1-1 relationship with the objects in arr1"
>>
>> If the objects are interlinked, rather than trying to keep two separate
>> arrays and sorting them side-by-side (which can easily go wrong), you
>> could simply connect the pairs into their own arrays all inside another
>> array.
>>
>> This has the benefit that once you put the pair into their own array,
>> they are connected without you having to worry about having to do
>> everything the same with array1 and array2.
>>
>> Then you can iterate through the large array like this:
>>
>> arr.each { |subarray| some_method( subarray[0], subarray[1] ) }
>>
>> In this example you can access each of the smaller arrays inside your
>> array. [0] is each object and [1] is each otherobject
>>
>> Or like this:
>>
>> arr.each { |object, otherobject| some_method( object, otherobject ) }
>>
>> This example is functionally the same as the previous one, but you're
>> using parallel assignment to place each object from the array into its
>> own variable so it's easier to read.
>>
>> Using this approach, you can sort the larger array containing objects
>> and otherobjects by whatever criteria you want, and they'll stay
>> together as a pair within the larger array.
>>
>> This will sort each array within the parent by the first object's id:
>>
>> arr = arr.sort_by { |object, otherobject| object.id }
>>
>> This does the same thing, but with the second object's id:
>>
>> arr = arr.sort_by { |object, otherobject| otherobject.id }
>>
>> The best way to grasp how this is works is to do it in IRB and play
>> around with the results.
>
> I just learned something new about ordering arrays! However this doesn't
> actually solve the original problem. Your solution expects both arrays
> to be properly sorted, and then keeps them together if one or the other
> is re-ordered.
>
> Originally only one of the arrays was properly sorted, and the other had
> then to be ordered to match.
>
> Here is some better sample data:
> terms = [
>     {:id=>3, :name=>"term1", :version=>2},
>     {:id=>4, :name=>"term2", :version=>2},
>     {:id=>8, :name=>"term3", :version=>1}
> ]
>
> arr2 = [
>     {:term_id=>4, :name=>"assoc1"},
>     {:term_id=>8, :name=>"assoc2"},
>     {:term_id=>3, :name=>"assoc3"}
> ]
>
> so 'terms' is properly sorted, and now we want arr2 to follow that
> order. So after our operation arr2 should look like:
>
> arr2 = [
>     {:term_id=>3, :name=>"assoc3"},
>     {:term_id=>4, :name=>"assoc1"},
>     {:term_id=>8, :name=>"assoc2"}
>
> ]
>
> These are ActiveRecord objects. A SQL solution is possible but the query
> is painfully long due to complex associations. Since the arrays are
> usually small 3-5 records, i was hoping i could just sort them
> programmatically.

Did you try Robert Klemme's solution? Translated to this new example:

arr2.sort_by {|o| arr1.find_index {|a| o[:term_id] == a[:id]}}

=> [{:term_id=>3, :name=>"assoc3"}, {:term_id=>4, :name=>"assoc1"},
{:term_id=>8, :name=>"assoc2"}]

Jesus.