Adding a tr function to Groovy Lists

tr.groovy

def tr = { inputs, outputs ->
  (inputs,outputs) = [inputs,outputs].collect { it instanceof List ? it : [ it ] }
  assert inputs.size() == outputs.size(), 'tr: Inputs and outputs must be the same size'
  delegate.collect { item ->
    inputs.indexOf( item ).with { idx ->
      idx == -1 ? item : outputs[ idx ]
    }
  }
}

List.metaClass.tr = tr

def names = ['A','B','C','A','D']

assert ['X','B','C','X','D'] == names.tr( 'A', 'X' )
assert ['X','B','Y','X','D'] == names.tr( ['A','C'], ['X','Y'] )