How, with Ruby, can I access and compare these nested array values?

Question

I have this nested array:

[[1, 2, 3],                                                                   
 [1, 3, 6],                                                                   
 [1, 4, 12],                                                                  
 [1, 5, 5],                                                                   
 [1, 2, 3],                                                                   
 [1, 8, 7],                                                                   
 [2, 3, 3],                                      
 [2, 4, 9],                                      
 [2, 5, 2],                                      
 [2, 8, 4],                                      
 [3, 4, 6],                                      
 [3, 8, 1],                                      
 [5, 8, 2],                                      
 [2, 8, 4],                                      
 [7, 8, 9]]

and I am trying to find a succinct but readable way of:

comparing and finding the maximum value from those values in index position[2] (i.e. 3rd element in each nested array) within each of the nested arrays.
Returning the neighbouring values at index[0] and [1] from the same nested array containing the maximum value from point 1.

I've unsuccessfully played around with various methods such as #max, #max_by, #group_by, #with_index but I'm now at the stage where I could just do with some enlightenment from a more capable brain and programmer then me.

spickermann · Accepted Answer · 2023-03-07 14:41:58Z

6

Finding the nested array with the max value on the last element:

input = [[1, 2, 3], [1, 3, 6], [1, 4, 12], [1, 5, 5], [1, 2, 3], [1, 8, 7], [2, 3, 3], [2, 4, 9], [2, 5, 2], [2, 8, 4], [3, 4, 6], [3, 8, 1], [5, 8, 2], [2, 8, 4], [7, 8, 9]]
input.max_by(&:last)
#=> [1, 4, 12]

And to only return its first two values:

input.max_by(&:last).take(2)
#=> [1, 4]

answered Mar 7, 2023 at 14:41

spickermann

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4 Comments

jbk Over a year ago

Ha ha, amazing, so simple when you know how!!!! Thanks @spickermann.

engineersmnky Over a year ago

@jbk please note max_by will return the first object in the event of a tie, meaning if input << [10,11,12] the result of this post would be the same.

Cary Swoveland Over a year ago

A slight variant is input.max_by(&:last).values_at(0, 1), which is perhaps slightly more descriptive. Alternatively, *v01, _v2 = input.max_by(&:last), where the desired result is v01 #=> [1, 4] and, while not needed (as signalled to the reader by the variable name beginning with an underscore), having the maximum value _v2 #=> 12 might be helpful in testing.

engineersmnky Over a year ago

@CarySwoveland it's a shame we can't use the trailing comma parallel assignment syntax with the splat syntax.

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