Ruby on Rails method to calculate percentiles - can it be refactored?
ruby, ruby-on-rails
Solution
Some remarks:
- If a particular index of an `Array` does not exist, `[]` will return `nil`, so your initial check for an empty `Array` is unnecessary.
- You should not `sort!` the `Array` argument, because you are affecting the order of the items in the `Array` in the code that called your method. Use `sort` (without `!`) instead.
- You don't actually use `arr_length` after assignment.
- A `return` statement on the last line is unnecessary in Ruby.
- There is no standard definition for the percentile function (there can be a lot of subtleties with rounding), so I'll just assume that how you implemented it is how you want it to behave. Therefore I can't really comment on the logic.
That said, the function that you wrote can be written much more tersely while still being readable.
def calculate_percentile(array, percentile)
array.sort[(percentile * array.length).ceil - 1]
end
Problem
I have written a method to calculate a given percentile for a set of numbers for use in an application I am building. Typically the user needs to know the 25th percentile of a given set of numbers and the 75th percentile. My method is as follows: ``` def calculate_percentile(array,percentile) #get number of items in array return nil if array.empty? #sort the array array.sort! #get the array length arr_length = array.length #multiply items in the array by the required percentile (e.g. 0.75 for 75th percentile) #round the result up to the next whole number #then subtract one to get the array item we need to return arr_item = ((array.length * percentile).ceil)-1 #return the matching number from the array return array[arr_item] end ``` This looks to provide the results I was expecting but can anybody refactor this or offer an improved method to return specific percentiles for a set of numbers?