From: Josselin <josselin@...>
Date: 2007-03-26T00:50:10+09:00
Subject: splitting an array into sub_arrays ...need advice

I have an array similar to this example  (after sorting it on a[i][1] 
and a[i][2])

start_array = [ [1, 1, 1, 0], [2, 1, 1, 0], [3, 1, 1, 0], [4, 1, 2, 0], 
[5, 1, 2, 0], [6, 2, 1, 0], [7, 2, 1, 0], [8, 2, 2, 0], [9, 2, 2, 0], 
[10, 2, 3, 0] ]

I am trying to split it, into sub_arrays according to similarelements  
a[i][1] and a[i][2] ,
to get another array like this one :

resulting_array = [  [[1, 1, 1, 0], [2, 1, 1, 0], [3, 1, 1, 0]]  ,   
[[4, 1, 2, 0], [5, 1, 2, 0]]  ,  [[6, 2, 1, 0], [7, 2, 1, 0]]  , [[8, 
2, 2, 1], [9, 2, 2, 0]]  , [[10, 2, 3, 0]]   ]

-----
herafter is how I proceed..  but I am not sure where I go.. is it not 
too complicated (not even saying DRY..)

I am using a[i][3] as a counter, so I can change its value, before 
executing the splitting

0.step(start_array.nitems-1, 1) do |i|
start_array[i][3] = 0
end

then, I wrote this method

def count_markers(a)
	n = 0
	0.step(a.nitems-2, 1) do |i|
	if (a[i][1] == a[i+1][1]) && (a[i][2] == a[i+1][2])
		n = n+1
		a[i][3] = n
	else
		a[i][3] = n +1
		n = 0
	end
	end
a[a.nitems-1][3] = 1 if a[a.nitems-1][3] == 0
end

 so I get  a count of the number of elements to put in each sub-array

counted_array = count_markers(start_array)
which gives me :
counted_array => [ [1, 1, 1, 1], [2, 1, 1, 2], [3, 1, 1, 3], [4, 1, 2, 
1], [5, 1, 2, 2], [6, 2, 1, 1], [7, 2, 1, 2], [8, 2, 2, 1], [9, 2, 2, 
2], [10, 2, 3, 1] ]

now I don't see how to split it to get the resulting array

resulting_array = [  [[1, 1, 1, 0], [2, 1, 1, 0], [3, 1, 1, 0]]  ,   
[[4, 1, 2, 0], [5, 1, 2, 0]]  ,  [[6, 2, 1, 0], [7, 2, 1, 0]]  , [[8, 
2, 2, 1], [9, 2, 2, 0]]  , [[10, 2, 3, 0]]   ]
where resulting_array.nitems = 5

resulting_array[0] = [[1, 1, 1, 0], [2, 1, 1, 0], [3, 1, 1, 0]] ... and so on