Argthtjtr

I'm trying to modify an array by deleting values that match a unique ID, but then stop once the first 5 values of the array are valid (i.e. their IDs do not match the undesired ones). If the array has a count <= 5, then this suffices:

all_items = [{"id" => "id01"},{"id" => "id02"},{"id" => "id03"},{"id" => "id04"}]

exclude_ids = ["id01","id02"]

all_items.delete_if { |item| exclude_ids.include?(item["id"])}

and the desired output is [{"id" => "id03"},{"id" => "id04"}].

But in the case where the total count of the array is >= 5, I want to delete only as many of the first items as necessary until the first 5 elements (all_items[0..4]) are all valid within the set criterion, and then stop iterating. If I were to do this:

all_items = [{"id" => "id01"},{"id" => "id02"},{"id" => "id03"},{"id" => "id04"},{"id" => "id05"},{"id" => "id06"},{"id" => "id07"},{"id" => "id08"},{"id" => "id09"},{"id" => "id10"}]

exclude_ids = ["id01","id02","id07"]

all_items.delete_if { |item| exclude_ids.include?(item["id"])}

return all_items[0..4]

I do get the desired output, [{"id" => "id03"},{"id" => "id04"},{"id" => "id05"},{"id" => "id06"},{"id" => "id08"}]. But I want the delete_if to completely stop once it reaches the point where all_items[0..4] already contains 5 valid elements. In this instance, I would want it to break after {"id" => "id08"}, and not even check the remaining values. (If, however, while the delete_if is running, the total count dips below 5, then it should continue iterating over all remaining elements, as it would fall into the category of the first piece of code I posted above, where the count <= 5.)

I know there is a delete_if.with_index, but I'm not sure if it's appropriate in this context, especially since the index would be shifting as items are deleted.

To summarize my question: is there a way to delete as many first items from an array as is required until array[0..x] is populated by desired values, and then stop checking/deleting any remaining items once that count of x is reached?

termination_threshold = 5

all_items = (1..20).to_a

  #=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]

exclusions = [1,2,7]



all_items.reject! do |n|

  break if termination_threshold.zero?

  exclude = exclusions.include? n

  termination_threshold -= 1 if exclude

  exclude

end

  #=> [3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]



all_items

  #=> [3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]

The following could be used if only an array containing the first termination_threshold valid elements of all_items were desired:

all_items.each_with_object() do |e,arr|

  arr << e unless exclusions.include?(e)

  break arr if arr.size == termination_threshold

end

  #=> [3, 4, 5, 6, 8]

If you delete from the original object you end up with all the items that had not been deleted. So, I gues it is better to move just the desired items to a new object:

all_items.each_with_object() { |item, ary| ary << item if !exclude_ids.include?(item["id"]) and ary.size < 5 }



#=> [{"id"=>"id03"}, {"id"=>"id04"}, {"id"=>"id05"}, {"id"=>"id06"}, {"id"=>"id08"}]

You can use Enumerator::Lazy to achieve what you want:

all_items = [{"id" => "id01"},{"id" => "id02"},{"id" => "id03"},{"id" => "id04"},{"id" => "id05"},{"id" => "id06"},{"id" => "id07"},{"id" => "id08"},{"id" => "id09"},{"id" => "id10"}]

exclude_ids = ["id01","id02","id07"]

all_items.lazy.reject {|item| exclude_ids.include?(item['id']) }.first(5)