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