Building a hash in a conditional way

Question

I am using Ruby on Rails 3.0.10 and I would like to build an hash key\\value pairs in a conditional way. That is, I would like to add a key and its related value if a condition

Answer 1

In case you want to add few keys under single condition, you can use merge:

hash = {
  :key1 => value1,
  :key2 => value2,
  :key3 => value3
}

if condition
  hash.merge!(
    :key5 => value4,
    :key5 => value5,
    :key6 => value6
  )
end

hash

Answer 2

Keep it simple:

hash = {
  key1: value1,
  key3: value3,
}

hash[:key2] = value2 if condition

This way you also visually separate your special case, which might get unnoticed if it is buried within hash literal assignment.

Answer 3

I use merge and the ternary operator for that situation,

hash = {
  :key1 => value1,
  :key3 => value3,
  ...
}.merge(condition ? {:key2 => value2} : {})

Answer 4

Simple as this:

hash = {
  :key1 => value1,
  **(condition ? {key2: value2} : {})
}

Hope it helps!

Answer 5

First build your hash thusly:

hash = {
  :key1 => value1,
  :key2 => condition ? value2 : :delete_me,
  :key3 => value3
}

Then do this after building your hash:

hash.delete_if {|_, v| v == :delete_me}

Unless your hash is frozen or otherwise immutable, this would effectively only keep values that are present.