Correct Way to Populate an Array with a Range in Ruby

Correct way to populate an Array with a Range in Ruby

You can create an array with a range using splat,

>> a=*(1..10)
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

using Kernel Array method,

Array (1..10)
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

or using to_a

(1..10).to_a
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Create array in Ruby with begin value, end value and step for float values

For floats with custom stepping you can use Numeric#step like so:

-1.25.step(by: 0.5, to: 1.25).to_a
# => [-1.25, -0.75, -0.25, 0.25, 0.75, 1.25] 

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If you are looking on how to do this with integer values only, see this post or that post on how to create ranges and simply call .to_a at the end. Example:

(-1..1).step(0.5).to_a
# => [-1.0, -0.5, 0.0, 0.5, 1.0] 

Create array of n items based on integer value

You can just splat a range:

[*1..10]
#=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Ruby 1.9 allows multiple splats, which is rather handy:

[*1..3, *?a..?c]
#=> [1, 2, 3, "a", "b", "c"]

how to create an array with ranges using an array with integer in ruby(rails)?

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

How fast is Ruby's method for converting a range to an array?

The method is actually slightly worse than O(n). Not only does it do a naive iteration, but it doesn't check ahead of time what the size will be, so it has to repeatedly allocate more memory as it iterates. I've opened an issue for that aspect and it's been discussed a few times on the mailing list (and briefly added to ruby-core). The problem is that, like almost anything in Ruby, Range can be opened up and messed with, so Ruby can't really optimize the method. It can't even count on Range#size returning the correct result. Worse, some enumerables even have their size method delegate to to_a.

In general, it shouldn't be necessary to make this conversion, but if you really need array methods, you might be able to use Array#fill instead, which lets you populate a (potentially pre-allocated) array using values derived from its indices.

How to select array elements in a given range in Ruby?

You can use ranges in the array subscript:

arr[100..200]

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