Collections conversion in Groovy can be achieved with some of collect* features. One of them, collectEntries(), iterates through given collection and returns a key-value pair. This pair is after stored in associated Map.
@Test void "should convert List to Map"() { List<String> clubs = ["Arsenal", "Bastia", "Wolfsburg"] Map<String, String> clubsMap = clubs.collectEntries { entry -> return [entry.charAt(0).toString(), entry] } assertThat(clubsMap['A']).isEqualTo('Arsenal') assertThat(clubsMap['B']).isEqualTo('Bastia') assertThat(clubsMap['W']).isEqualTo('Wolfsburg') }