// ĠBuild Ġa Ġmap Ġthat Ġstores Ġthe Ġcustomers Ġliving Ġin Ġa Ġgiven Ġcity Ċ fun ĠShop . group Customers By City ( city Ġ: ĠCity ): ĠMap < City , ĠList < Customer >> Ġ= ĊĠĠĠĠĠĠĠ Ġcustomers . groupBy Ġ{ Ġit . city Ġ} Ċ