Ruby index of array elements

my_array.index.with_index{|value,index| my_array[index,6].uniq.size==1} 

This is a kind of tweak, if you mean "optimised" just in the way code looks like.If you mean optimised performance. it does not fit.

In first iteration, I am getting array of repeating elements sequence and then I proceed further with logic,

groups = my_array[1..-1].inject([[my_array[0]]]) { |m, n| m.last[0] == n ? m.last << n : m << [n]; m } # => [[100], [101], [100], [102], [100, 100], [101], [100], [250], [251], [253], [260], [250], [200], [100, 100, 100, 100, 100, 100, 100, 100, 100], [120]] groups[0,groups.index(groups.sort { |a,b| a.count <=> b.count }.last)].flatten.count # => 14 

Using regex, it can be precise and simple.

I assume the objective is to find the index of the first element of the longest sequence of equal elements in the given array.

my_array = [100, 101, 100, 102, 100, 100, 101, 100, 250, 251, 253, 260, 250, 200, 100, 100, 100, 100, 100, 100, 100, 100, 100, 120] 

Here that would be 14, the index of 100 that is followed by 8 more 100's.

We can do that as follows.

my_array.each_index.chunk { |i| my_array[i] }. max_by { |_,a| a.size }. last. first #=> 14 

The steps are as follows.

enum0 = my_array.each_index #=> #<Enumerator: [100, 101, 100,..., 100, 120]:each_index> 

We can see the elements that will be generated by this enumerator by converting it to an array.

enum0.to_a #=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, # 17, 18, 19, 20, 21, 22, 23] 

Continuing,

enum1 = enum0.chunk { |i| my_array[i] } #=> #<Enumerator: #<Enumerator::Generator:0x000058d8d09ec8a0>:each> 

In view of the above expression's return value, enum1 could be thought of as a compound enumerator, though Ruby has no such concept. Let's see the values enum1 will generate.

enum1.to_a #=> [[100, [0]], [101, [1]], [100, [2]], [102, [3]], [100, [4, 5]], # [101, [6]], [100, [7]], [250, [8]], [251, [9]], [253, [10]], # [260, [11]], [250, [12]], [200, [13]], # [100, [14, 15, 16, 17, 18, 19, 20, 21, 22]], # [120, [23]]] 

Continuing,

a = enum1.max_by { |v,a| a.size } #=> [100, [14, 15, 16, 17, 18, 19, 20, 21, 22]] 

As v is not used in the block, this expression would customarily be written:

a = enum1.max_by { |_,a| a.size } 

The presence of the underscore (a valid local variable) signals to the reader that that block variable is not used in the block calculation. The last two steps are as follows.

b = a.last #=> [14, 15, 16, 17, 18, 19, 20, 21, 22] b.first #=> 14 

See Enumerable#chunk and Enumerable#max_by.

my_array = [100, 101, 100, 102, 100, 100, 101, 100, 250, 251, 253, 260, 250, 200, 100, 100, 100, 100, 100, 100, 100, 100, 100, 120] index_and_repetitions = lambda { |my_array| stk = {} previous = my_array[0] last_index = 0 stk[last_index] = 1 my_array.drop(0).each_with_index{|item, index| if item == previous stk[last_index] += 1 else last_index = index stk[last_index] = 1 previous = item end } stk } stk = index_and_repetitions.call(my_array) puts stk.key(stk.values.max) 

you can find benchmark results(compared to others answers) from here.