Each With Index

each_with_index gives a block both the current value and its position.

index-aware iteration Index-aware iteration is useful when output depends on position as well as value.

                            start_number
                            start_number = 1 (default)start_number = 0start_number = 5
                        

                            each_with_index.rb
                        
Replay: real traced execution (multi-file project)

                            start_number = 1
items = ["red", "blue", "green"]

items.each_with_index do |item, index|
  label = "#{index + start_number}:#{item}"
  puts label
end
start_number = 0
items = ["red", "blue", "green"]

items.each_with_index do |item, index|
  label = "#{index + start_number}:#{item}"
  puts label
end
start_number = 5
items = ["red", "blue", "green"]

items.each_with_index do |item, index|
  label = "#{index + start_number}:#{item}"
  puts label
end

                        
1start_number ← 1, items ← ["red", "blue", "green"]1start_number→ 1 = 1  #@start_number=0, 52items→ ["red", "blue", "green"] = ["red", "blue", "green"]34items["red", "blue", "green"].each_with_index do |item, index|5  label = "#{index + start_number}:#{item}"6  puts label7end⋯
2label ← 1:redpass 1 of 3⋯4items.each_with_index do |itemred, index0|5  label→ 1:red = "#{index0 + start_number1}:#{itemred}"6  puts label1:red7end⋯output1:redAll 3 passes — pass 1 is the card abovepassitemindexitemslabel
1red0—1:red
2blue1—2:blue
3green2["red", "blue", "green"]3:green
1start_number ← 0, items ← ["red", "blue", "green"]1start_number→ 0 = 02items→ ["red", "blue", "green"] = ["red", "blue", "green"]34items["red", "blue", "green"].each_with_index do |item, index|5  label = "#{index + start_number}:#{item}"6  puts label7end⋯
2label ← 0:redpass 1 of 3⋯4items.each_with_index do |itemred, index0|5  label→ 0:red = "#{index0 + start_number0}:#{itemred}"6  puts label0:red7end⋯output0:redAll 3 passes — pass 1 is the card abovepassitemindexitemslabel
1red0—0:red
2blue1—1:blue
3green2["red", "blue", "green"]2:green
1start_number ← 5, items ← ["red", "blue", "green"]1start_number→ 5 = 52items→ ["red", "blue", "green"] = ["red", "blue", "green"]34items["red", "blue", "green"].each_with_index do |item, index|5  label = "#{index + start_number}:#{item}"6  puts label7end⋯
2label ← 5:redpass 1 of 3⋯4items.each_with_index do |itemred, index0|5  label→ 5:red = "#{index0 + start_number5}:#{itemred}"6  puts label5:red7end⋯output5:redAll 3 passes — pass 1 is the card abovepassitemindexitemslabel
1red0—5:red
2blue1—6:blue
3green2["red", "blue", "green"]7:green

pass	`item`	`index`	`items`	`label`
1	red	0	—	1:red
2	blue	1	—	2:blue
3	green	2	["red", "blue", "green"]	3:green

pass	`item`	`index`	`items`	`label`
1	red	0	—	0:red
2	blue	1	—	1:blue
3	green	2	["red", "blue", "green"]	2:green

pass	`item`	`index`	`items`	`label`
1	red	0	—	5:red
2	blue	1	—	6:blue
3	green	2	["red", "blue", "green"]	7:green