pattern for maps that take n-dimensional inputs and yield m-dimensional inputs

day_labels.rb

      # Draw day labels, e.g. "Mon 1/30", "Tue 1/31", "Wed 2/1" etc.
      day_labels = (0...DAYS_PER_WEEK).map {|d| (start_date + d).strftime("%a   %-m/%-d")}

      # HEY GISTERS LOOK HERE: Okay, I have a loop that iterates 0 to
      # 6, and I need this for the day_label in question, but I *also*
      # need to know the x-coordinate at which to draw the label. What
      # I would like in this SPECIFIC case, is a loop construct that
      # somehow yields the day_label and x-coordinate, perhaps as a
      # pair, which I guess I could do with a map. But in general I'm
      # looking for a loop construct that accepts n-dimensional inputs
      # (e.g. arrays of 1-element) and emits m-dimensional outputs
      # (e.g. arrays of 3-elements).
      (0...DAYS_PER_WEEK).each do |i|
        x = (TODO_COLUMNS+i) * COLUMN_WIDTH
        text_box day_labels[i], at: [x,PAGE_HEIGHT], height: HEADER_HEIGHT, width: COLUMN_WIDTH, align: :center, valign: :center, style: :bold
      end

But in general I'm looking for a loop construct that accepts n-dimensional inputs (e.g. arrays of 1-element) and emits m-dimensional outputs (e.g. arrays of 3-elements).

Array#zip might be convinced to do your bidding here.

a = [1, 2, 3]
b = [:a, :b, :c]

a.zip(b)
# => [[1, :a], [2, :b], [3, :c]]

a.zip(b).each { |foo, bar| puts "#{foo} - #{bar}" }
#1 - a
#2 - b
#3 - c
# => [[1, :a], [2, :b], [3, :c]]

So this is the answer I was looking for but I don't know if it's really any better:

  day_labels.map.with_index {|label, i| [label, (TODO_COLUMNS+i)*COLUMN_WIDTH]}.each do |label, x|
    text_box label, at: [x,PAGE_HEIGHT], height: HEADER_HEIGHT, width: COLUMN_WIDTH, align: :center, valign: :center, style: :bold
  end

Yeah, not too much difference — Array#zip probably wins in my book since it lets you collect and validate your inputs separately.

day_labels = (0...DAYS_PER_WEEK).map { |d| (start_date + d).strftime("%a   %-m/%-d") }
x_offsets  = (0...DAYS_PER_WEEK).map { |d| (TODO_COLUMNS+d)*COLUMN_WIDTH }

day_labels.zip(x_offsets).each do |label, x|
  text_box_with_label_at(label, x)
end

Plus another sneaky refactoring. Because I have a problem.