You have two choices:
The first and most performant is to use associateBy
function that takes two lambdas for generating the key and value, and inlines the creation of the map:
val map = friends.associateBy({it.facebookId}, {it.points})
The second, less performant, is to use the standard map
function to create a list of Pair
which can be used by toMap
to generate the final map:
val map = friends.map { it.facebookId to it.points }.toMap()