Find largest integer from objects within array and return a key value pair

Question

I'm trying to write a function that takes as a parameter an array of objects, like this: function getOldest([{name:john, age:69}, {name:jane, age:28}, {name:paul, age: 19}])

The function would check the age property of the objects and find the largest value, and then return the name property.

getOldest([{name: john, age: 35}, {name: jane, age: 20}, {...}])
returns "john"

Additionally, if two key value pairs share the same value, as in two people have the same age, it would return an array instead.

getOldest([{name: john, age: 20}, {name: jane, age: 20}, {...}])
returns ['john', 'jane']

I've been trying to figure out how to do this for about five hours now but I just can't figure it out.

trying to write a function - so far you've written the name of a function ... keep trying — Jaromanda X
– Jaromanda X, Commented Dec 20, 2017 at 6:21
@JaromandaX funny. I tried looping through the array using a for loop selecting the values of age with person[i].age and then an if statement that would go through the values, adding the largest one to an empty variable but that didn't work since I couldn't link that back to the object. Took me a few tries with different versions before I realized I don't know enough to write the code I want. — Leo
– Leo, Commented Dec 20, 2017 at 6:37
the answer is tow use array reduce - this should be as much of an answer as you get, as you've shown zero effort — Jaromanda X
– Jaromanda X, Commented Dec 20, 2017 at 6:38

Jonas Wilms · Accepted Answer · 2017-12-20 06:44:12Z

1

I would always return an array to keep consistency:

 function getOldest(arr){
   const old = arr.reduce((acc, {age}) => Math.max(acc, age), 0);
   return arr.filter(({age}) => age === old);
 }

At first it goes through the array with reduce and finds the oldest age, then it returns the array filtered by that.

If you want to reduce in one step:

 function getOldest(arr){
   var old = 0;
   return arr.reduce((arr, {name, age}) => {
     if(age > old){
       old = age;
       return [name];
     }
     if(age === old) return arr.concat(name);
     return arr;
  }, []);
 }

edited Dec 20, 2017 at 6:44

answered Dec 20, 2017 at 6:22

Jonas Wilms

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6 Comments

RobG Over a year ago

Why not post it here as a runnable snippet? You shouldn't need filter, just make the accumulator from the appropriate names.

Jonas Wilms Over a year ago

@robG cause the <> button is disabled on mobile devices ;/

RobG Over a year ago

You're keen… I don't bother on my iPhone 5. ;-)

Jonas Wilms Over a year ago

@robg added reducing in one step however thats slightly more convoluted on my opinoon ;)

Jonas Wilms Over a year ago

@gurvinder thanks for pointing out, fixed it ;)

|

gurvinder372 · Accepted Answer · 2017-12-20 06:27:00Z

0

Use sort, then filter and finally map

var arr = [{name:"john", age:69}, {name:"jane", age:28}, {name:"paul", age: 19}];
arr.sort( ( a, b ) => b.age - b.age ); //sort by age in reverse
var maxAge = arr[ 0 ].age; //find max age
var output  = arr.filter( a => a.age == maxAge ).map( a => a.name ); //returns array of max age name

Demo

var arr = [{
  name: "john",
  age: 69
}, {
  name: "jane",
  age: 28
}, {
  name: "paul",
  age: 19
}];
arr.sort((a, b) => b.age - b.age); //sort by age in reverse
var maxAge = arr[0].age; //find max age
var output = arr.filter(a => a.age == maxAge).map(a => a.name); //returns array of max age name
console.log(output);

Or find the maxAge first using map

var arr = [{name:"john", age:69}, {name:"jane", age:28}, {name:"paul", age: 19}];
var maxAge = Math.max.apply( null, arr.map( a => a.age ) );
var output  = arr.filter( a => a.age == maxAge ).map( a => a.name ); //returns array of max age name

Demo

var arr = [{name:"john", age:69}, {name:"jane", age:28}, {name:"paul", age: 19}];
var maxAge = Math.max.apply( null, arr.map( a => a.age ) );
var output  = arr.filter( a => a.age == maxAge ).map( a => a.name ); //returns array of max age name
console.log( output );

edited Dec 20, 2017 at 6:27

answered Dec 20, 2017 at 6:23

gurvinder372

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2 Comments

RobG Over a year ago

sort affects the original array. One reduce is sufficient.

gurvinder372 Over a year ago

@RobG Added another method

RobG · Accepted Answer · 2017-12-20 06:37:57Z

0

Since there are answers already… it seems to me reduce is sufficient. Also, I think it's better to always return an array. Functions that return different types depending on some random criterion aren't friendly:

function getOldest(data) {
  var max = -Infinity;
  return data.reduce((acc, obj) => {
    obj.age > max? (acc = [obj.name]) && (max = obj.age) :
    obj.age == max? acc.push(obj.name): null;
    return acc;
  },[]);
}

var data = [{name: 'paul', age: 19}, 
            {name: 'john', age: 69},
            {name: 'jane', age: 28},
            {name: 'fred', age: 13},
            {name: 'tom' , age: 69}];

console.log(getOldest(data));

answered Dec 20, 2017 at 6:37

RobG

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4 Comments

Jonas Wilms Over a year ago

Why the boolean algebra if you are returning afterwards?

RobG Over a year ago

@JonasW.—because it's shorter than if..else and means there's only one return (since the callback needs to return the accumulator). I'm open to a better way.

Jonas Wilms Over a year ago

(acc, obj) => obj.age > max && (max = age) && [obj.name] || obj.age === max && acc.concat(obj) || acc

RobG Over a year ago

@JonasW.—that has errors, doesn't return what the OP wants or in the correct format. :-(

Margu · Accepted Answer · 2017-12-20 07:04:33Z

0

var myarray = [{name: 'john', age: 35}, {name: 'jane', age: 20}];
var oldest = getoldest(myarray);
alert(oldest.name);

and in the function you could do something like this

function getoldest(myarray){
 var oldest = Math.max.apply(Math,myarray.map(function(myarray){return myarray.age;}));
 var obj = myarray.find(function(o){return o.age == oldest;});
 return obj;
};

This way you could use the returned object for something else.

edited Dec 20, 2017 at 7:04

answered Dec 20, 2017 at 6:46

Margu

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Comments

Catalin · Accepted Answer · 2017-12-20 10:46:10Z

0

 function getOldest(arr){

    return arr.reduce( function(acc,current){
       if (acc.age > current.age) {
          return acc
       } else { return current}
    }).name

 }

Edit: It's actually the best method here, just a reduce and that's it, no sorting or filtering.

edited Dec 20, 2017 at 10:46

answered Dec 20, 2017 at 6:27

Catalin

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4 Comments

RobG Over a year ago

This just returns the first object with the max age, not what the OP wants. If it was the correct result, consider the simpler: return acc.age > current.age? acc : current, ;-)

Catalin Over a year ago

No it's not! Next time just check my answer in a compiler.

RobG Over a year ago

You could have posted it here as a runnable snippet. It doesn't accommodate duplicates, so not what the OP wants. It will also throw an error if arr is empty as you haven't provided an initial accumulator.

Catalin Over a year ago

Rob, just be more attentive next time.

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