How to build hash from array

Question

This is a rock paper scissors game. From irb, game.class says it's an array. I hope to find the name of the person who won the game (in this case Player2).

game = [["Player1", "P"], ["Player2", "S"]]

The approach that comes to mind is to return a Hash with the name values split up. Then search that hash via the value to get the player name.

h = Hash.new(0)
game.collect do |f|
  h[f] = f[1]
end
h
#=> {["Player1", "P"]=>"P", ["Player2", "S"]=>"S"}

This is close but no cigar. I want

{"Player1" => "P", "Player2" => "S"}

I tried again with inject method:

game.flatten.inject({}) do |player, tactic| 
  player[tactic] = tactic  
  player 
end
#=> {"Player1"=>"Player1", "P"=>"P", "Player2"=>"Player2", "S"=>"S"}

This did not work:

Hash[game.map {|i| [i(0), i(1)] }]
#=> NoMethodError: undefined method `i' for main:Object

I would appreciate some pointers to something that will help me understand.

related: bugs.ruby-lang.org/issues/666

tokland
– tokland

2012-10-20 11:10:27 +00:00
Commented Oct 20, 2012 at 11:10 — tokland
– tokland, Commented Oct 20, 2012 at 11:10

Benoît · Accepted Answer · 2012-10-20 10:36:21Z

3

You can simply do this too.

game = [["Player1", "P"], ["Player2", "S"]]
#=> [["Player1", "P"], ["Player2", "S"]]
Hash[game]
#=> {"Player1"=>"P", "Player2"=>"S"}

answered Oct 20, 2012 at 10:36

Benoît

14.5k7 gold badges65 silver badges88 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

sf2k Over a year ago

holy cow! can you explain what happened there?

sf2k Over a year ago

I'll play around with this more later. Thank you

sf2k Over a year ago

Thanks that really simplifies the thinking.

sf2k Over a year ago

I think I would have ended up in daisy chain hell even though inject is perfectly fine below. I'll select this as the answer as it got me thinking straight about hashes, although both are right

xdazz · Accepted Answer · 2012-10-20 10:31:45Z

2

Use:

game.inject({}){ |h, k| h[k[0]] = k[1]; h }

answered Oct 20, 2012 at 10:31

xdazz

161k38 gold badges255 silver badges278 bronze badges

3 Comments

sf2k Over a year ago

that works too! I have to figure out what that h[k[0]] is doing.

sf2k Over a year ago

I think I see, it's actually a nested element call to the first pair item then link to the second item of the same pair. Is that a fair translation?

sf2k Over a year ago

Hmm....Oh for each element in game it builds the next section. Man I'm glad I got to sleep. Thank you

Andrew Grimm · Accepted Answer · 2012-10-21 21:51:07Z

2

Using each_with_object means you don't need to have two statements in the block, like in xdazz's answer

game.each_with_object({}){ |h, k| h[k[0]] = k[1] }

You can make this even more readable by destructuring the second block parameter

game.each_with_object({}){ |hash, (name, tactic)| hash[name] = tactic }

answered Oct 21, 2012 at 21:51

Andrew Grimm

82.3k58 gold badges210 silver badges355 bronze badges

1 Comment

sf2k Over a year ago

That's pretty interesting, thank you. It has a nice readability to it

Drenmi · Accepted Answer · 2015-10-13 05:47:38Z

0

You can use Ruby's built in Array#to_h method for this:

game.to_h
#=> {"Player1"=>"P", "Player2"=>"S"}

edited Oct 13, 2015 at 5:47

Drenmi

8,8064 gold badges46 silver badges52 bronze badges

answered Oct 12, 2015 at 13:06

lalit.sethi143

1461 silver badge5 bronze badges

Collectives™ on Stack Overflow

How to build hash from array

4 Answers 4

4 Comments

3 Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

4 Comments

3 Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related