Ruby: inject_with_index

Here’s a useful extension:

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module Enumerable
  def inject_with_index(injected)
    each_with_index{ |obj, index| injected = yield(injected, obj, index) }
    injected
  end
end

Example usage

This is useful for a number of reasons, one being when you have two separate arrays of related data that you’d like to combine into a single array. For example, I’m pulling in my public github projects in the about section by scraping GitHub’s HTML (using Hpricot).

I’m using inject_with_index to organize the parsed response into a single array, which I can then iterate through and easily output.

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def github_projects
  # ...

  titles = html / 'div.title b a'
  descriptions = html / 'div.description'

  titles.inject_with_index([]) do |projects, title, index|
    projects << [title, descriptions[index]]
  end
end

And it’s also less worry to cache that single array than trying to keep track of titles and descriptions separately later on. A win-win.

Now, hopefully this doesn’t already exist. I couldn’t find it, but that doesn’t mean I didn’t reinvent the wheel.