getting specific values from objects within arrays

Question

Considering the following array which includes several objects within it, I tried to get specific values in one single array.To put it delicately,I wanted to pull out the name of people who were in the "red" team.

// 
    const array = [
      {
        username: "Mike",
        team: "red",
        score: 20,
     items: ["bat", "book", "gloves"]
  },
  {
    username: "Moe",
    team: "blue",
    score: 30,
    items: ["cellphone", "backpack", "cards"]
  },
  {
    username: "Ellie",
    team: "red",
    score: 15,
    items: ["ball", "canteen", "crayon"]
  },
  {
    username: "little_joe",
    team: "green",
    score: 1,
    items: ["book", "pencil"]
  },

];

//using filter method :

const filterArray=array.filter((num)=>{ if (num.team==="red" ){ return num.username}});
console.log(filterArray);

//result : an array including two objects full of unwanted values.

What should I do to get one single array with only desired value ( not two big objects) ?

I'm trying to get an array like this : (2)►[Mike,Ellie]

Cory Kleiser · Accepted Answer · 2018-05-25 18:02:04Z

1

One way to do this would be to use Array.prototype.filter and Array.prototype.map. However, the preferred way would be to use Array.prototype.reduce as it will be much more efficient.

Like this:

const array = [{
    username: "Mike",
    team: "red",
    score: 20,
    items: ["bat", "book", "gloves"]
  },
  {
    username: "Moe",
    team: "blue",
    score: 30,
    items: ["cellphone", "backpack", "cards"]
  },
  {
    username: "Ellie",
    team: "red",
    score: 15,
    items: ["ball", "canteen", "crayon"]
  },
  {
    username: "little_joe",
    team: "green",
    score: 1,
    items: ["book", "pencil"]
  },

];

const newArray = array.reduce((n, val) => {
  if(val.team == "red") n.push(val.username);
  return n;
}, []);

console.log(newArray);

edited May 25, 2018 at 18:02

answered May 25, 2018 at 17:40

Cory Kleiser

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2 Comments

jedzej Over a year ago

it's fine, but why this gimmick usage of ternary operator val.team == "red" ? n.push(val.username) : null; instead of straightforward if(val.team == "red") n.push(val.username); ?

Cory Kleiser Over a year ago

@jedzej you're right. I shouldn't be using ternary for ternary's sake. Answer updated. Thanks.

Barmar · Accepted Answer · 2018-05-25 17:26:10Z

1

filter doesn't return the values that were returned by the callback, it just checks if it's truthy, and uses that to decide whether to return the array element.

You can do it in two steps. First use filter to get just the elements with team === "red", then use map to extract username:

const filterArray = array.filter(num => num.team === "red").map(num => num.username);

You can also do it in one step using reduce, I'll leave that as an exercise for the reader.

answered May 25, 2018 at 17:26

Barmar

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Comments

Anton Harniakou · Accepted Answer · 2018-05-25 17:40:23Z

1

As suggested by @Barmar, here's a version using reduce:

const redTeamPeople = array.reduce((people, { team, username }) => {
  if (team === "red") {
    people.push(username);
  }

  return people;
}, []);

answered May 25, 2018 at 17:40

Anton Harniakou

8807 silver badges13 bronze badges

1 Comment

Cory Kleiser Over a year ago

This is the preferred method. More concise and much faster given a very large array with a lot of data.

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