Ruby each_with_index offset

Question

Can I define the offset of the index in the each_with_index loop iterator? My straight forward attempt failed:

some_array.each_with_index{|item, index = 1| s         


        

Answer 1

1) The simplest is to substitute index+1 instead of index to the function:

some_array.each_with_index{|item, index| some_func(item, index+1)}

but probably that is not what you want.

2) The next thing you can do is to define a different index j within the block and use it instead of the original index:

some_array.each_with_index{|item, i| j = i + 1; some_func(item, j)}

3) If you want to use index in this way often, then define another method:

module Enumerable
  def each_with_index_from_one *args, &pr
    each_with_index(*args){|obj, i| pr.call(obj, i+1)}
  end
end

%w(one two three).each_with_index_from_one{|w, i| puts "#{i}. #{w}"}
# =>
1. one
2. two
3. three

---

Update

This answer, which was answered a few years ago, is now obsolete. For modern Rubies, Zack Xu's answer will work better.

Answer 2

Yes, you can

some_array[offset..-1].each_with_index{|item, index| some_func(item, index) }
some_array[offset..-1].each_with_index{|item, index| some_func(item, index+offset) }
some_array[offset..-1].each_with_index{|item, index| index+=offset; some_func(item, index) }

UPD

Also I should notice that if offset is more than your Array size it will though an error. Because:

some_array[1000,-1] => nil
nil.each_with_index => Error 'undefined method `each_with_index' for nil:NilClass'

What can we do here:

 (some_array[offset..-1]||[]).each_with_index{|item, index| some_func(item, index) }

Or to prevalidate offset:

 offset = 1000
 some_array[offset..-1].each_with_index{|item, index| some_func(item, index) } if offset <= some_array.size

This is little hacky

UPD 2

As far as you updated your question and now you need not Array offset, but index offset so @sawa solution will works fine for you

Answer 3

Another approach is to use map

some_array = [:foo, :bar, :baz]
some_array_plus_offset_index = some_array.each_with_index.map {|item, i| [item, i + 1]}
some_array_plus_offset_index.each{|item, offset_index| some_func(item, offset_index) }

Answer 4

If some_index is somehow meaningful, then consider using a hash, rather than an array.