How to use the higher order function sort() on computed value of objects in an array

Question

This is an array of friends... with start and end of the friendship:) I want to sort the array by the computed duration of the friendship (end minus start)

const friends = [
  { name: "Michael", start: 1981, end: 2004 },
  { name: "Joe", start: 1992, end: 2008 },
  { name: "Sara", start: 1999, end: 2007 },
  { name: "Marcel", start: 1989, end: 2010 },
];

I was able to do this by first adding a friendshipDuration value and in a next step be sorting the array.

for (let i=0; i < companies.length; i++ ) {
  // friends[i].friendshipDuration = friends[i].end - friends[i].start;
  friends[i]["friendshipDuration"] = friends[i]["end"] - friends[i]["start"];
}

const sortedfriends = friends.sort(function(c1, c2) {
  if(c1.friendshipDuration > c2.friendshipDuration) {
    return 1;
  } else {
    return -1;
  }
})
console.log(sortedfriends);

Yeah, but I would love to do this in one step... compute the friendshipDuration in the process of the higher order function sort().

const sortedfriends2 = friends.sort(function(c1, c2) {
  const compDuration = friends.end - friends.start;
  if(c1.compDuration > c2.compDuration) {
    return 1;
  } else {
    return -1;
  }
})

console.log(sortedfriends2);

There is this (c1, c1) => c1 - c2) tricky bit I'm reading about but I don't know where to put it. I'm a Javascript beginner and wanted to challenge myself with higher order functions;)

Help is very much appreciated.

Answer 1

You need to calculate the duration for both c1 and c2 and then compare those two calculated values each time the comparison function is called.

const sortedfriends2 = friends.sort(function(c1, c2) {
  const c1FriendshipDuration = c1.end - c1.start;
  const c2FriendshipDuration = c2.end - c2.start;
  if(c1FriendshipDuration > c2FriendshipDuration) {
    return 1;
  } else {
    return -1;
  }
});

console.log(sortedfriends2);

Answer 2

You do not need to compute the friendship duration in advance, unless you need it for later. You can compute it on the fly as follows:

 const friends = [ { name: "Michael", start: 1981, end: 2004 }, { name: "Joe", start: 1992, end: 2008 }, { name: "Sara", start: 1999, end: 2007 }, { name: "Marcel", start: 1989, end: 2010 }, ]; const sortedfriends = friends.sort( (a,b) => (a.end - a.start) - (b.end - b.start) ); console.log( sortedfriends );

Need Duration?

Just in case you need friendshipDuration for later, you can use Array#map to compute it, followed by sorting:

 const friends = [ { name: "Michael", start: 1981, end: 2004 }, { name: "Joe", start: 1992, end: 2008 }, { name: "Sara", start: 1999, end: 2007 }, { name: "Marcel", start: 1989, end: 2010 }, ]; const sortedfriends = friends.map( f => ({...f,friendshipDuration:f.end - f.start}) ).sort( (a,b) => a.friendshipDuration - b.friendshipDuration ); console.log( sortedfriends );