how to find best matching element in array of numbers?

Question

I need help with something that seems simple but confuses me. Trying to write some fuzzy matching method that copes with differences in format between what value is computed as needed, and which are actually available from a selection list.

The value (option strike price) is always a computed Float like 85.0 or Int.

The array contains numbers in string form, unpredictable in either increment or whether they will be shown rounded to some decimal (including extra zeros like 5.50) or no decimal (like 85), eg.:

select_list = ["77.5", "80", "82.5", "85", "87.5", "90", "95", "100", "105"]

I am unsure how to write a simple line or two of code that will return the closest matching element (by number value) as it appears in the array. For example, if select_list.contains? 85.0 returned "85"

Actually, the selection choices come from a Watir::Webdriver browser.select_list(:id, "lstStrike0_1") HTML object whose visible text (not HTML value) are those numbers; maybe there is a more direct way to just call browser.select_list(:id, "lstStrike0_1").select X without having to figure out in Watir how to convert all those choices into a Ruby array?

Adley

Another question https://mcmap.net/q/904399/-turning-a-select_list-options-into-a-string-array-in-watir-webdriver/1069375 illuminated me how to easily convert the Watir select_list into the needed array: selectContent = browser.select_list(:id, "lstStrike0_1").options.map(&:text) – Adley

Answer 1

xs = ["77.5", "80", "82.5", "85", "87.5", "90", "95", "100", "105"]
xs.min_by { |x| (x.to_f - 82.4).abs } 
#=> "82.5"

Bib

Most concise way I see. For my purposes the complete solution combined into one line was $browser.select_list(:id, "lstStrike0_0").select ( strikelist = $browser.select_list(:id, "lstStrike0_0").options.map(&:text) ).min_by { |x| (x.to_f - sigitem[:strikel]).abs } – Adley

Answer 2

I'm not a ruby coder so this might not be the best way to do it

def select_closest(list, target)                               
    return (list.map {|x| [(x.to_f - target).abs, x]}).min[1]  
end                                                            

select_list = ["77.5", "80", "82.5", "85", "87.5", "90", "95", "100", "105"] 

puts select_closest(select_list, 81)  # yields 80

Silden

I esp. like that you considered inexact number values (81 vs closest 80) even though I didn't explicitely mention that, but is liable to occur. Thanks! – Adley