FAQ: Data Structures - (Re)Introduction to Iteration

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This community-built FAQ covers the “(Re)Introduction to Iteration” exercise from the lesson “Data Structures”.

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[jimike101]

Beginner question.
Could I get a clarification about Hashes and especially placeholder symbol |x, y| in the below example?
Especially this line,
family.each { |x, y| puts “#{x}: #{y}”

I’m very confused about how the placeholder section |x, y| is laid out. I can understand what it means but it seems kind of “wrong”, therefore I think my mental model of it must be wrong too.

I’ve understood the key-value pain to be very, very similar to an index number and a value that number would refer to.
eg. say,
variable = “igloo”, var[1] index location would refer to value “g” (as index starts a 0).

Well I’m extremely confused about why in the placeholder text you’d refer to |x, y|. That’s almost as if you be using |the location of a value, and the value itself|.
Was this just an improvised answer because both the value and location was useful, eg Homer, and Dad, or is the |x, y| format to refer to |hash location, value| something we’ll use again and again. Thanks.
Sorry if I was confusing. I’m an extreme newbie with any coding language and only less than a week into my Ruby study.

friends = [“Milhouse”, “Ralph”, “Nelson”, “Otto”]

family = { “Homer” => “dad”,
“Marge” => “mom”,
“Lisa” => “sister”,
“Maggie” => “sister”,
“Abe” => “grandpa”,
“Santa’s Little Helper” => “dog”
}

friends.each { |x| puts “#{x}” }
family.each { |x, y| puts “#{x}: #{y}” }

[pashmentinstructure]

I also have the same question about "{ |x| puts “#{x}” }
I saw it in the previous exercise and that part was not explained at all.

[midlindner]

When we iterate over an array or hash with .each the index isn’t used. .each just returns each element in an array or each key => value pair in a hash.

friends.each {|x| puts "#{x}"} #iterating over the friends array
#.each returns each element 1 at a time. x is the temporary placeholder for 
#the element. Whatever code is included in the code block can access the element
#referred to by x

family.each { |x, y| puts "#{x}: #{y}" } #iterating over the family hash
#x is the placeholder for the key. y is the placeholder for the value

Hope this helps.

[pashmentinstructure]

@midlindner

{|x| puts “#{x}”}

Yes, it does. Thank you!

[chip9111048520]

I’m fooling around with the code here, and I don’t understand the results of one of my experiments.

friends.each.downcase { |x| puts “#{x}” }

Returns the error “undefined method for downcase”

but

friends.each { |x| puts “#{x}”.downcase }

works as expected.

What gives?