merge.rb

a = { foo: 'foo', bar: 'bar' }
b = { foo: 'fooo' }

# Reconcile duplicate keys
a.merge(b) {|k, old_v, new_v| [old_v, new_v].min}
# => { foo: 'foo', bar: 'bar' }

# Ever wanted Hash#map to return a hash? This is a workaround
a.merge(a) {|k, v| v.upcase}
# => { foo: "FOO", bar: "BAR" }