Find largest sub array out of ruby multidimensional array

Question

I want to find out the largest sub array out of a multidimensional array in ruby. I have a multidimensional array as follows :

array = [[1,20],[2,40],[5,100],[7,15],[9,22]]

I want the first element of the sub array which second element is largest like in the above example I want the 5 as an output because second element of sub array [5,100] is largest which is 100. The output would be 5.

And if more then one element are maximum than i want all these.

Ex: array = [[1,20],[2,40],[5,100],[7,15],[9,22],[12,100]]

The out put in this case would be [5,12]

Thanks in advance.

Answer 1

You can use the Enumerable#max_by method to select the max element, and then project that element to the result value.

array.max_by{|a| a[1]}[0]

UPDATE:

If you want all the elements with the maximum value, you can first get the max value from the array, and then filter the array with that value.

max_value = array.max_by{|a| a[1]}[1]
results = array.select{|a| a[1] == max_value}.map(&:first)

You may use one line expression, but I think that's less readable

array.group_by{|a| a[1]}.max_by{|k,v| k}[1].map(&:first)