A 15 minute tutorial on Ruby iterators like each(), reduce() and map()

1. RUBY ITERATORS
IN 15 MINUTES OR LESS

2. WHAT YOU’LL NEED FROM
PREVIOUS LESSONS
BLOCKS
ARRAYS AND HASHES
RAISE YOUR HAND IF YOU DON’T FEEL
COMFORTABLE WITH ALL OF THESE...

3. THE COMMON ITERATORS
.TIMES()
.EACH()
.COLLECT(), .MAP(), .MAP!()
.REDUCE(), .INJECT()

4. WHAT YOU’LL ITERATE OVER
ARRAYS
HASHES
ANYTHING THAT IMPLEMENTS
“ENUMERABLE”

5. THE SIMPLEST POSSIBLE EXAMPLE
5.times { puts “hello”}

6. THE SIMPLEST POSSIBLE EXAMPLE
5.times { puts “hello”}
AN ITERATOR

7. THE SIMPLEST POSSIBLE EXAMPLE
5.times { puts “hello”}
A BLOCK
AN ITERATOR

8. A MORE USEFUL EXAMPLE
GIVEN:
some_data = [
{name: ”tim c”},
{name: “larry”},
{name: “lindsey”},
{name: “curly”},
{name: “moe”}
]
THEN:
PRINT EVERYONE’S NAME ON THE SCREEN

9. THE SOLUTION (EACH)
some_data.each do |i|
puts i[:name]
end

10. WHY?
ITS EASIER TO READ (ONCE YOU’RE USED TO
IT)
YOU’LL MAKE FEWER DUMB MISTAKES

11. THE NON-ITERATOR WAY
num = some_data.length - 1
for i in 0..num do
puts some_data[i][:name]
end

12. YOU DECIDE
num = some_data.length - 1
for i in 0..num do
puts some_data[i][:name]
end
some_data.each do |i|
puts i[:name]
end
VS.

13. NEXT PROBLEM
GIVEN:
some_data = [
{name: ”tim c”},
{name: “larry”},
{name: “lindsey”},
{name: “curly”},
{name: “moe”}
]
THEN:
GATHER AN ARRAY OF JUST THE NAMES

14. THE SOLUTION (MAP)
names = some_data.map do |i|
i[:name]
end

15. ALSO PERFECTLY GOOD
(COLLECT)
names = some_data.collect do |i|
i[:name]
end

16. LAST, CALCULATE SOMETHING
GIVEN:
some_data = [
{name: ”tim c”},
{name: “larry”},
{name: “lindsey”},
{name: “curly”},
{name: “moe”}
]
THEN:
COUNT HOW MANY NAMES START WITH “L”

17. THE SOLUTION (REDUCE)
count = some_data.reduce(0)
do |so_far, i|
if i[:name].start_with?(“l”)
so_far = so_far + 1
end
so_far
end

18. PULLING BACK THE CURTAIN
THIS IS LITERALLY ALL THE CODE IN THE
RUBY .EACH() ITERATOR
def each
for 0..self.length - 1 do
yield self[i]
end
end

19. ...THERE ARE MORE. BUT YOU’LL
HARDLY EVER USE THEM.
STEP, DOWNTO, UPTO
FIND, FIND_ALL, SELECT, CYCLE
EACH_SLICE
CHUNK, REJECT
EACH_WITH_INDEX
NEARLY EVERYTHING IN ENUMERABLE: HTTP://
WWW.RUBY-DOC.ORG/CORE-2.1.1/ENUMERABLE.HTML

20. SOME REVIEW
WHICH ITERATOR WOULD YOU USE TO....
CALCULATE THE AVERAGE CHARACTER
COUNT IN AN ARRAY OF STRINGS

21. SOME REVIEW
WHICH ITERATOR WOULD YOU USE TO....
SEND AN EMAIL FOR EACH ADDRESS IN AN
ARRAY OF ADDRESSES

22. SOME REVIEW
WHICH ITERATOR WOULD YOU USE TO....
SPLIT AN ARRAY OF FULL NAMES (IE. “TIM
CULL”) INTO AN ARRAY OF FIRST NAME/
LAST NAME TUPLES (IE. [“TIM”,”CULL”])

23. EXERCISE
NOW, LET’S ACTUALLY DO THAT LAST ONE
SPLIT AN ARRAY OF FULL NAMES (IE. “TIM
CULL”) INTO AN ARRAY OF FIRST NAME/
LAST NAME TUPLES (IE. [“TIM”,”CULL”])