My problem is that I need to do efficient lookups of if a 2 element array and their corresponding value is nil. So if I have the following arrays:
arr1 = [
[1, 2, 100],
[3, 4, nil],
[5, 6, 101]
]
I want something like
h = {
[1, 2] => 100,
[3, 4] => nil,
[5, 6] => 101
}
So I can do something like:
error = []
arr2 = [
[1,2],
[3,4],
[7,8]
]
arr2.each do |val|
if h.include?(val)
if h[val] == nil
error << "Value is nil"
else
# Do something
end
else
error << "Key doesn't exist"
end
end
Given that overwriting or ignoring duplicates is acceptable per your comment.
You can use Enumerable#each_with_object to iterate the Array and create a Hash like so
arr1 = [
[1, 2, 100],
[3, 4, nil],
[5, 6, 101],
[1, 2, nil],
]
arr1.each_with_object({}) do |(*first_two,last),obj|
obj[first_two] = last
end
#=> {[1, 2]=>nil, [3, 4]=>nil, [5, 6]=>101}
You can ignore duplicates in a similar fashion
arr1.each_with_object({}) do |(*first_two,last),obj|
obj[first_two] = last unless obj.key?(first_two)
end
#=> {[1, 2]=>100, [3, 4]=>nil, [5, 6]=>101}
Explanation:
each_with_object({}) will pass each element of of arr1 to the block along with an object (a Hash in this case)
(*first_two,last),obj - *first_two will collect everything up to last and obj is our Hash
obj[first_two] = last simple Hash key assignment
each_with_object returns the object (obj Hash in this case)
Update as recommended by @Stefan in ruby >= 2.7 you could also use
arr1.to_h {|*first_two,last| [first_two, last] }
This version will overwrite keys
arr1 = [
[1, 2, 100],
[3, 4, nil],
[5, 6, 101]
]
result = {}
arr1.each { |i| result[i.first(2)] = i.last }
=> {[1, 2]=>100, [3, 4]=>nil, [5, 6]=>101}
You can destructure every subarray during mapping and then convert result to hash with Array#to_h method
arr1 = [
[1, 2, 100],
[3, 4, nil],
[5, 6, 101],
[1, 2, nil],
]
arr1.map { |*first_two, last| [first_two, last] }.to_h
# => {[1, 2]=>nil, [3, 4]=>nil, [5, 6]=>101}
Duplicates will be overwritten