Best way to iterate over multiple arrays?

Question

What's is the best (beauty and efficient in terms of performance) way to iterate over multiple arrays in Ruby? Let's say we have an arrays:

a=[x,y,z]
b=['a','b','c']

and I want this:

x a
y b
z c

Thanks.

possible duplicate of [What's the 'Ruby way' to iterate over two arrays at once](http://stackoverflow.com/questions/3580049/whats-the-ruby-way-to-iterate-over-two-arrays-at-once) — dee-see, Sep 09 '14 at 21:05

score 6 · Answer 1 · answered Jan 27 '11 at 14:52

An alternative is using each_with_index. A quick benchmark shows that this is slightly faster than using zip.

a.each_with_index do |item, index|
  puts item, b[index]
end

Benchmark:

a = ["x","y","z"]
b = ["a","b","c"]

Benchmark.bm do |bm|
  bm.report("ewi") do
    10_000_000.times do
      a.each_with_index do |item, index|
        item_a = item
        item_b = b[index]
      end
    end
  end
  bm.report("zip") do
    10_000_000.times do
      a.zip(b) do |items|
        item_a = items[0]
        item_b = items[1]
      end
    end
  end
end

Results:

      user     system      total        real
ewi  7.890000   0.000000   7.890000 (  7.887574)
zip 10.920000   0.010000  10.930000 ( 10.918568)

ruby 1.9.2p136 (2010-12-25 revision 30365) [x86_64-darwin10.6.0] — Dylan Markow, Jan 27 '11 at 22:27

score 4 · Accepted Answer · answered Jan 27 '11 at 13:35

4

The zip method on array objects:

a.zip b do |items|
    puts items[0], items[1]
end

answered Jan 27 '11 at 13:35

kelloti

8,705
5
46
82

3

You could also so something like `a.zip(b) { |first, second| p [first, second] }` instead of indexing `items`. – Michael Kohl Jan 27 '11 at 13:47

score 2 · Answer 3 · answered Jan 27 '11 at 13:36

2

>> a=["x","y","z"]
=> ["x", "y", "z"]
>> b=["a","b","c"]
=> ["a", "b", "c"]
>> a.zip(b)
=> [["x", "a"], ["y", "b"], ["z", "c"]]
>>

answered Jan 27 '11 at 13:36

kurumi

25,121
5
44
52

score 1 · Answer 4 · answered Oct 23 '15 at 15:11

I like to use transpose when iterating through multiple arrays using Ruby. Hope this helps.

bigarray = []
bigarray << array_1
bigarray << array_2
bigarray << array_3
variableName = bigarray.transpose

variableName.each do |item1,item2,item3|

# do stuff per item
# eg 
puts "item1"
puts "item2"
puts "item3"

end

score 1 · Answer 5 · edited May 23 '17 at 10:33

1

See What is a Ruby equivalent for Python's "zip" builtin?

edited May 23 '17 at 10:33

Community

1
1

answered Jan 27 '11 at 13:35

Björn Lindqvist

19,221
20
87
122

Best way to iterate over multiple arrays?

5 Answers5

Linked