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up vote 0 down vote favorite

i have an array with sorted integers

array = [1,4,10,14,22]

i would like to create from array before an

array_with_ranges = [[0..1],[2..4],[5..10],[11..14],[15..22]]

i cant create a right iterator, i'm newbie in rails. In every ranges i have end_range value, but don't know how to set a start_range value? in most ranges in array_with_ranges the start_range is a end_range before +1 (except [0..1])

any solutions or ideas?

thank you for answers.

p.s.: happy new 2015 year

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3 Answers 3

up vote 2 down vote accepted

Add a helper value of -1, later on remove it.

array = [1,4,10,14,22]
array.unshift(-1)
ranges = array.each_cons(2).map{|a,b| a+1..b} #=>[0..1, 2..4, 5..10, 11..14, 15..22]

array.shift
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thank you! brilliant solution) –  anndrew78 Jan 13 at 19:51
up vote 0 down vote

Just keeping track of the previous value takes care of it:

2.1.5 :001 > array = [1,4,10,14,22]
 => [1, 4, 10, 14, 22] 
2.1.5 :002 > previous = 0
 => 0 
2.1.5 :003 > array.map { |i| rng = previous..i; previous = i + 1; rng }
 => [0..1, 2..4, 5..10, 11..14, 15..22]

I imagine there's a slicker way to do it though.

edit: Of course there is, building on @steenslag's answer:

2.1.5 :001 > array = [1, 4, 10, 14, 22]
 => [1, 4, 10, 14, 22] 
2.1.5 :002 > ([-1] + array).each_cons(2).map { |a,b| (a + 1)..b }
 => [0..1, 2..4, 5..10, 11..14, 15..22]
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up vote 1 down vote

You can iterate on all elements of the array and save the previous value in the external variable, like this:

last = -1 
array.collect {|x| prev = last; last = x; (prev+1..x)}
share|improve this answer
    
excellent!it's a good method to do it. –  user3673267 Jan 12 at 3:20

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