Iterating through multiple values in a hash and returning a value

Question

I have a hash:

  hash_example = {777 =>[dog,brown,3], 123=>[cat,orange,2]}

I want to go through the hash array value and determine based on the third element which pet is the oldest age. I would choose the max for my method, the part where I figure out which value is associated with max and returning it to the screen is the part I am not getting, or am I completly lost? I threw the third value in there for educational purpose on how to compare different elements of the array.

b = hash_example.values.max{|k,b,c| b<=>c } 
print b

Greg Dan · Accepted Answer · 2009-11-14 10:37:57Z

3

In ruby 1.8.7 there is a nice max_by method.

hash_example.values.max_by {|a| a[2]}

answered Nov 14, 2009 at 10:37

Greg Dan

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Simone Carletti · Accepted Answer · 2009-11-14 10:18:19Z

2

max iterates all items returned by values and each item is an array itself. That's the point you are missing.

> hash_example.values
# => [["dog", "brown", 3], ["cat", "orange", 2]]

max doesn't return the value you are comparing against, instead, it returns the item that satisfies the comparison. What does it mean in practice? Here's the "working" version of your script

> hash_example.values.max{|a,b| a[2]<=>b[2] }
# => ["dog", "brown", 3]

As you can see, the returned value is the full item not the element used for the comparison. If you only want the third element you have to use inject.

> hash_example.values.inject(0) {|t,i| i[2] > t ? i[2] : t }
# => 3

answered Nov 14, 2009 at 10:18

Simone Carletti

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2 Comments

Carl Smotricz Over a year ago

Yours is the better analysis and the better solution. I withdraw.

Matt Over a year ago

Thanks for the in depth explination. It makes alot more sense now!

EmFi · Accepted Answer · 2009-11-14 18:05:57Z

1

Similar to Greg Dan's response for earlier versions of Ruby.

hash_example.values.collect{|a|a[2]}.max

answered Nov 14, 2009 at 18:05

EmFi

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1 Comment

Matt Over a year ago

how do I take my value from max and return a different element in the same array? Obviously dog is 3 for .max but how do I puts that becasue the element in that array is .max I want to know print the string Dog? I didn't fully understand the .inject block

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