Ruby - Checking if one array key/value is NOT present in another one

Question

With ruby, I am trying to look from the first array key[:nb].value, if there is NOT one similar pair in the second one.

Considerate below arrays contain thousands of elements:

arr1 = [{"nb"=>"5df54g54df", "active"=>true, "brand"=>"aisle"},{"nb"=>"5jghfj264", "active"=>false, "brand"=>"leg"},{"nb"=>"5qwercv546", "active"=>true, "brand"=>"gem"}]

arr2 = [{"nb"=>"5df54g54df", "active"=>false, "brand"=>"aisle"},{"nb"=>"5jghfj264", "active"=>false, "brand"=>"gem"}]

So far I was thinking something like that:

p (arr1.map(&:nb).find do |nb, val| arr2.map(&:nb)).?Include?(nb && val)

Would you have a suggestion, please?

After finding those who are not present, for those with similar nb.value, how to highlight the difference they have individually? Tks!

Answer 1

My understanding of the question is as follows: "Find the first element h of arr1 (a hash), such that there is no element g of arr2 (a hash) for which h["nb"] == g["nb"] is true".

arr1 = [
  {"nb"=>"5df54g54df", "active"=>true, "brand"=>"aisle"},
  {"nb"=>"5jghfj264", "active"=>false, "brand"=>"leg"},
  {"nb"=>"5qwercv546", "active"=>true, "brand"=>"gem"}
]

arr2 = [
  {"nb"=>"5df54g54df", "active"=>false, "brand"=>"aisle"},
  {"nb"=>"5jghfj264", "active"=>false, "brand"=>"gem"}
]

require 'set'

nbs2 = arr2.each_with_object(Set.new) { |h,st| st << h["nb"] }
  #=> #<Set: {"5df54g54df", "5jghfj264"}>

arr1.find { |h| !nbs2.include?(h["nb"]) }​
  #=> {"nb"=>"5df54g54df", "active"=>true, "brand"=>"aisle"}

One could omit the construction of the set nbs2 and compute

arr1.find { |h| !arr2.include?(h["nb"]) }

but that requires a linear search through arr2 for each element h of arr1 that is examined. By contrast, determining whether a set contains a specific element is much faster, with the time required to do so almost independent of the size of the set.

Answer 2

Try this

arr1 = [
  {"nb"=>"5df54g54df", "active"=>true, "brand"=>"aisle"},
  {"nb"=>"5jghfj264", "active"=>false, "brand"=>"leg"},
  {"nb"=>"5qwercv546", "active"=>true, "brand"=>"gem"}
]

arr2 = [
  {"nb"=>"5df54g54df", "active"=>false, "brand"=>"aisle"},
  {"nb"=>"5jghfj264", "active"=>false, "brand"=>"gem"}
]

# Just create a simple lambda for extracting nb values
 
extract_nb = ->(h) { h['nb'] }

# Using map just apply array intersection operation  
# for finding common key of 'nb'

p arr1.map(&extract_nb) & arr2.map(&extract_nb))

optput

["5df54g54df", "5jghfj264"]