reverse order of Array in Ruby with index counter

Question

I have an array @dates, that are UTC dates, and in increasing order. I want to flip the indices of the array so that the dates are in descending order. I am familiar with JS an Java, and don't know how to either use a pointer/index counter in ruby.

@dates = [//dates are in here already]

@reverseDates = []
@dates.each do |d|
  @reverseDates << @dates.last
end

@dates = @reverseDates

Part of the issue as well is that I think it is duplicating the last index of @dates, not moving it to the other array when it pushes.

So I got it it working by prepending the array, but how do you include index counters in Ruby to accomplish this?

@reverseDates = []
@dates.each do |d|
  @reverseDates.unshift(d)
end

@dates = @reverseDates

In the first example @dates.last never changes in the each because @dates never changes in the each. See Enumerable#each_with_index for how to iterate with an index; however, this is not the real problem, nor the real solution. — user166390
– user166390, Commented Dec 24, 2012 at 3:45
I recommend reading the full API of the Enumerable module from A to Z, each one of these methods is so powerful! — akuhn
– akuhn, Commented Dec 24, 2012 at 4:40

Jeff Peterson · Accepted Answer · 2012-12-24 03:37:41Z

6

Ruby has reversing an array built in:

@dates.reverse!

From http://ruby-doc.org/core-1.8.7/Array.html#method-i-reverse-21

answered Dec 24, 2012 at 3:37

Jeff Peterson

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1 Comment

user166390 Over a year ago

I would recommend using reverse as I find that reducing side-effects creates easier-to-follow code and reduces surprises.

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