Samples to building an hash key\value pairs in a conditional way.

conditional_hash.rb

# case1
Hash.new.tap do |hash|
  hash[:key1] = value1 if condition_1
  hash[:key2] = value2 if condition_2
end

# case2
hash = {}
hash[:key1] = value1
hash[:key2] = value2 if condition_2
hash[:key3] = value3

# case3
hash = {
  key1: value1,
  key2: (value2 if condition_2),
  key3: value3,
}.compact 

# case4
hash = {
  key1: value1,
  key3: value3,
}
hash[:key2] = value2 if condition_2

# case5
hash = {
  key1: value1,
  key3: value3,
}.merge(condition_2 ? { key2: value2 } : {})

# case6
hash = {
  key1: value1,
  key3: value3,
}.tap { |h| h[:key2] = value2 if condition_2 }