Map data from array within a nested object-CodePudding

My goal is to map the length of the skills array for each user.

I start with this bit of JSON here:

    const txt = `{
    "Alex": {
        "email": "[email protected]",
        "skills": [
            "HTML",
            "CSS",
            "JavaScript"
        ],
        "age": 20,
        "isLoggedIn": false,
        "points": 30
    },
    "Asab": {
        "email": "[email protected]",
        "skills": [
            "HTML",
            "CSS",
            "JavaScript",
            "Redux",
            "MongoDB",
            "Express",
            "React",
            "Node"
        ],
        "age": 25,
        "isLoggedIn": false,
        "points": 50
    },
    "Brook": {
        "email": "[email protected]",
        "skills": [
            "HTML",
            "CSS",
            "JavaScript",
            "React",
            "Redux"
        ],
        "age": 30,
        "isLoggedIn": true,
        "points": 50
    },
    "Daniel": {
        "email": "[email protected]",
        "skills": [
            "HTML",
            "CSS",
            "JavaScript",
            "Python"
        ],
        "age": 20,
        "isLoggedIn": false,
        "points": 40
    },
    "John": {
        "email": "[email protected]",
        "skills": [
            "HTML",
            "CSS",
            "JavaScript",
            "React",
            "Redux",
            "Node.js"
        ],
        "age": 20,
        "isLoggedIn": true,
        "points": 50
    },
    "Thomas": {
        "email": "[email protected]",
        "skills": [
            "HTML",
            "CSS",
            "JavaScript",
            "React"
        ],
        "age": 20,
        "isLoggedIn": false,
        "points": 40
    },
    "Paul": {
        "email": "[email protected]",
        "skills": [
            "HTML",
            "CSS",
            "JavaScript",
            "MongoDB",
            "Express",
            "React",
            "Node"
        ],
        "age": 20,
        "isLoggedIn": false,
        "points": 40
    }
}
`

I then parse it to the userObj variable:

const userObj = JSON.parse(txt, undefined);

Now this is where things get odd,

for (let user in userObj) {
  console.log(user); //returns several strings, rather than the objects themselves
}

and when I try to iterate over those objects, naturally I get unexpected results. I've tried many different approaches over the past few hours and haven't managed to implement anything that works.

Expected final result example:

{ 
Alex => 3,
Asab => 7,
Brooke => 5
}

CodePudding user response：

You can use Object.keys to do what you're looking for:

Object.keys(userObj).map((user) => {
  const userString = `${user} => ${userObj[user].skills.length}`;
  console.log(userString);
});

Results in:

Alex => 3
Asab => 8
Brook => 5
Daniel => 4
John => 6
Thomas => 4
Paul => 7

To accomplish this, map over each of userObj's keys, which are the users names, allowing us to access each user objects values, then we simply create our output string!

CodePudding user response：

The "for-in" loop returns a key in each iteration instead of the value of a field, so you should get the objects by userObj[user].

CodePudding user response：

First you should convert the JSON to an object. Then you should convert this object to an array, to map over that. But in th second step you can already print out to console anything.

const txt = `{
    "Alex": {
        "email": "[email protected]",
        "skills": [
            "HTML",
            "CSS",
            "JavaScript"
        ],
        "age": 20,
        "isLoggedIn": false,
        "points": 30
    },
    "Asab": {
        "email": "[email protected]",
        "skills": [
            "HTML",
            "CSS",
            "JavaScript",
            "Redux",
            "MongoDB",
            "Express",
            "React",
            "Node"
        ],
        "age": 25,
        "isLoggedIn": false,
        "points": 50
    },
    "Brook": {
        "email": "[email protected]",
        "skills": [
            "HTML",
            "CSS",
            "JavaScript",
            "React",
            "Redux"
        ],
        "age": 30,
        "isLoggedIn": true,
        "points": 50
    },
    "Daniel": {
        "email": "[email protected]",
        "skills": [
            "HTML",
            "CSS",
            "JavaScript",
            "Python"
        ],
        "age": 20,
        "isLoggedIn": false,
        "points": 40
    },
    "John": {
        "email": "[email protected]",
        "skills": [
            "HTML",
            "CSS",
            "JavaScript",
            "React",
            "Redux",
            "Node.js"
        ],
        "age": 20,
        "isLoggedIn": true,
        "points": 50
    },
    "Thomas": {
        "email": "[email protected]",
        "skills": [
            "HTML",
            "CSS",
            "JavaScript",
            "React"
        ],
        "age": 20,
        "isLoggedIn": false,
        "points": 40
    },
    "Paul": {
        "email": "[email protected]",
        "skills": [
            "HTML",
            "CSS",
            "JavaScript",
            "MongoDB",
            "Express",
            "React",
            "Node"
        ],
        "age": 20,
        "isLoggedIn": false,
        "points": 40
    }
}
`
let userArr = [];
let users = JSON.parse(txt)
for (userName in users) {
  const user = {userName, skillNumber: 0};
  user.skillNumber = users[userName].skills.length
  userArr.push(user);
}

const res = userArr.map(user=>`${user.userName} -> ${user.skillNumber}`)
console.log(res);

CodePudding user response：

If the parsing worked it shouldn't do that. Here's a working example.

const txt='{"Alex":{"email":"[email protected]","skills":["HTML","CSS","JavaScript"],"age":20,"isLoggedIn":false,"points":30},"Asab":{"email":"[email protected]","skills":["HTML","CSS","JavaScript","Redux","MongoDB","Express","React","Node"],"age":25,"isLoggedIn":false,"points":50},"Brook":{"email":"[email protected]","skills":["HTML","CSS","JavaScript","React","Redux"],"age":30,"isLoggedIn":true,"points":50},"Daniel":{"email":"[email protected]","skills":["HTML","CSS","JavaScript","Python"],"age":20,"isLoggedIn":false,"points":40},"John":{"email":"[email protected]","skills":["HTML","CSS","JavaScript","React","Redux","Node.js"],"age":20,"isLoggedIn":true,"points":50},"Thomas":{"email":"[email protected]","skills":["HTML","CSS","JavaScript","React"],"age":20,"isLoggedIn":false,"points":40},"Paul":{"email":"[email protected]","skills":["HTML","CSS","JavaScript","MongoDB","Express","React","Node"],"age":20,"isLoggedIn":false,"points":40}}';

const users = JSON.parse(txt);

const out = {};

for (const user in users) {
  console.log(user);
  out[user] = users[user].skills.length;
}

console.log(out);