How do I find the value of the key that I set with argument in Ruby?

Question

I am currently working on a project with Ruby. I don't know how to find the set of the value and key that has the same key as I gave with argument.

what I have tried is something like this below. but it doesn't work.

def find_target(type)
    target = type_list.find{|k,v| k == type}
    target
end


def type_list 
  type = {
    a: 1,
    b: 2,
    c: 3,
    d: 4
   }
  type
end

but instead of giving an argument of variable, I gave a string as an argument, and it worked.

def find_target(a)
    target = type_list.find{|k,v| k == a}
    target
end

• Edited What I really want find_target to do is returning a matched value. For example, when an argument is a, then it returns 1.

How can I solve this?

I would love you if you could help me. Thank you.

Answer 1

I think one thing tripping you up is that your type_list hash is keyed with symbols (rather than strings or the value of a variable). The syntax you're using:

{a: 1}

is just shorthand for this:

{:a => 1}

Which means "A Hash with one key: the symbol :a with the value 1 ". That's distinct from:

{'a' => 1} # Keyed with the string 'a'

and this:

a = 'something'
b = {a => 1} # Keyed with value of 'a' at the time of creating, ie: {'something' => 1}. Note that if you change the value of a, the hash key won't change.

What do you expect as your return value from find_target(:a) ? The find method on a Hash will return an Enumerator - mostly equivalent to a two-element Array, with the key and the value: {a: 1}.find{|k,v|k ==:a} will return [:a, 1] . Is that what you want?

If you just want to have the value 1 returned, then you're really doing a hash lookup, and you don't need any extra methods at all. A common way to do this would be to define type_list as a constant, and then just refer to it by key:

TYPE_LIST = {
  a: 1,
  b: 2,
  c: 3,
  d: 4
}

#Then to find the type:
TYPE_LIST[:a] # Returns '1'

You might want to use a find_type method to handle the case where the key doesn't match a type: a plain Hash lookup will return nil , which you might not want.

Hope this helps put you on the right path, but I'm happy to expand this answer if needed!