From: Joel Pearson <lists@...>
Date: 2013-06-18T04:12:41+09:00
Subject: Re: Compare and sort one array according to another.

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.

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