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

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.

CodePudding user response：

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);

CodePudding user response：

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 );