检查哈希映射数组中是否存在某些值

Question

I have an array of hash map. It looks like this:

params = []
CSV.foreach(......) do
  one_line_item = {}
  one_line_item[:sku] = "Hello"
  one_line_item[:value] = "20000"
  params << one_line_item
end

I want to check if :sku is in this array of hash or not. I am doing it like this:

# Reading new line of csv in a hash and saving it in a temporary variable (Say Y)
params.each do |p|
  if p[:sku] == Y[:sku]
    next
  end
end

I am iterating through the complete list for every value of sku, and thus time complexity is going for a toss [O(n^2)], need less to say it is useless.

Is there a way I can use include? ?

If I can get an array of values corresponding to the key :sku from the whole array in one shot, it would solve my problem. (I know I can maintain another array for these values but I want to avoid that)

One example of params

params = [{:sku=>"hello", :value=>"5000"}, {:sku=>"world", :value=>"6000"}, {:sku=>"Hi", :value=>"7000"}]

Answer 1

The any? and include? methods sound like what you need.

Example:

params.any? { |param| param.include?(:sku) }

This is an efficient way to do it, as it "short circuits", stopping as soon as a match is found.

Answer 2

So what you want is to collect a list of all SKUs. Are you looking to key sku => value?

Hash[*params.map { |p| [p[:sku], p[:value]] }.flatten]

That will give you a map of each sku to the value, which you can then do quick key lookups with sku_hash.key?(tester)

Answer 3

You may use rails_param gem for doing the same. I find it a very useful utility for validation request params in controller:

https://github.com/nicolasblanco/rails_param

# primitive datatype syntax
param! :integer_array, Array do |array,index|
  array.param! index, Integer, required: true
end

# complex array
param! :books_array, Array, required: true  do |b|
  b.param! :title, String, blank: false
  b.param! :author, Hash, required: true do |a|
    a.param! :first_name, String
    a.param! :last_name, String, required: true
  end
  b.param! :subjects, Array do |s,i|
    s.param! i, String, blank: false
  end
end