Creating an array out of a specific JSON Key-Value Pair

Question

Let's say I have a JSON array like this

[{"name":"Lenovo Thinkpad 41A4298","website":"google"},
{"name":"Lenovo Thinkpad 41A2222","website":"google"},
{"name":"Lenovo Thinkpad 41Awww33","website":"yahoo"},
{"name":"Lenovo Thinkpad 41A424448","website":"google"},
{"name":"Lenovo Thinkpad 41A429rr8","website":"ebay"},
{"name":"Lenovo Thinkpad 41A429ff8","website":"ebay"},
{"name":"Lenovo Thinkpad 41A429ss8","website":"rediff"},
{"name":"Lenovo Thinkpad 41A429sg8","website":"yahoo"}]

I want to get an array of all the names that have the website value equal to google.

Firstly, to filter the JSON array to contain only entries where the website is google, I have this:

var data_filter = data.filter( element => element.website =="google");
console.log(data_filter);

which gives the following result:

[{"name":"Lenovo Thinkpad 41A4298","website":"google"},
    {"name":"Lenovo Thinkpad 41A2222","website":"google"},
    {"name":"Lenovo Thinkpad 41A424448","website":"google"}]

What do I need to do next to get the name in a separate array. I tried doing this:

let new_array = [];
  new_array.push(data_filter.body.name)

which gives me an undefined error for name. I also tried:

new_array.push(data_filter.name)
  new_array.push(data_filter.body[0].name)

But none of the approaches work. What am I missing here?

FYI - JSON data and Filter approach is mentioned in this SO post - credits to the OP and answers.

I have a JSON Do you have something in JSON or an object? They're pretty different things — CertainPerformance
– CertainPerformance, Commented May 11, 2018 at 7:05
Your filter line won't work. You're assigning to every element.website with something truthy, so all items will pass the filter test. — CertainPerformance
– CertainPerformance, Commented May 11, 2018 at 7:07
What do you expect data_filter.body to be? You just logged data_filter as an array. — Bergi
– Bergi, Commented May 11, 2018 at 12:49

dodov · Accepted Answer · 2018-05-11 07:41:33Z

9

You need to use double equals sign to compare == instead of single =. When it’s single, you change (assign) element.website to "google". The result of that expression is the value you set, which is "google" and it is a truthy value and therefore all elements pass the test of filter().

var data = [{"name":"Lenovo Thinkpad 41A4298","website":"google"},
{"name":"Lenovo Thinkpad 41A2222","website":"google"},
{"name":"Lenovo Thinkpad 41Awww33","website":"yahoo"},
{"name":"Lenovo Thinkpad 41A424448","website":"google"},
{"name":"Lenovo Thinkpad 41A429rr8","website":"ebay"},
{"name":"Lenovo Thinkpad 41A429ff8","website":"ebay"},
{"name":"Lenovo Thinkpad 41A429ss8","website":"rediff"},
{"name":"Lenovo Thinkpad 41A429sg8","website":"yahoo"}];

var data_filter = data.filter( element => element.website == "google");

var names = data_filter.map(function (elem) {
  return elem.name;
});
console.log(names);

To get the names after you’ve filtered the results, use map().

Your code didn’t work because you try to access a property body of the filtered results. The filtered results consist of an array of your original results, but only the entries that pass the test. Since your original entries don’t have a body property, the filtered results won’t have it either. And also, you tried data_filter.body which will never exist because data_filter will always be an Array and arrays don’t have a body property.

1 Comment

demouser123 Over a year ago

Thanks for the link on filter method. I also found another helpful link here medium.com/@joomiguelcunha/…

gurvinder372 · Accepted Answer · 2018-05-11 07:06:15Z

4

Use map after filter (also correct = with === )

var data_filter = data.filter( element => element.website === "google").map( s => s.name );

Or if you don't want to iterate twice, use reduce

data.reduce( (a, c) => {
   c.website === "google" ? a.push( c.name ) : "";
   return a; //return accumulator
} , []); //initialize accumulator

answered May 11, 2018 at 7:06

gurvinder372

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Comments

Mihai Alexandru-Ionut · Accepted Answer · 2018-05-11 07:11:32Z

4

You can use map method in combination with filter and pass callback provided functions for each of them.

let data = [{"name":"Lenovo Thinkpad 41A4298","website":"google"}, {"name":"Lenovo Thinkpad 41A2222","website":"google"}, {"name":"Lenovo Thinkpad 41Awww33","website":"yahoo"}, {"name":"Lenovo Thinkpad 41A424448","website":"google"}, {"name":"Lenovo Thinkpad 41A429rr8","website":"ebay"}, {"name":"Lenovo Thinkpad 41A429ff8","website":"ebay"}, {"name":"Lenovo Thinkpad 41A429ss8","website":"rediff"}, {"name":"Lenovo Thinkpad 41A429sg8","website":"yahoo"}]

names = data.filter(function(item){
     return item.website == 'google';
}).map(function(item){
     return item.name;
});
console.log(names)

Another approach is to use arrow functions and destructure the arguments.

let data = [{"name":"Lenovo Thinkpad 41A4298","website":"google"}, {"name":"Lenovo Thinkpad 41A2222","website":"google"}, {"name":"Lenovo Thinkpad 41Awww33","website":"yahoo"}, {"name":"Lenovo Thinkpad 41A424448","website":"google"}, {"name":"Lenovo Thinkpad 41A429rr8","website":"ebay"}, {"name":"Lenovo Thinkpad 41A429ff8","website":"ebay"}, {"name":"Lenovo Thinkpad 41A429ss8","website":"rediff"}, {"name":"Lenovo Thinkpad 41A429sg8","website":"yahoo"}]

names = data.filter(({website}) => website == 'google').map(({name}) => name);
console.log(names)

edited May 11, 2018 at 7:11

answered May 11, 2018 at 7:06

Mihai Alexandru-Ionut

48.6k14 gold badges106 silver badges132 bronze badges

4 Comments

demouser123 Over a year ago

Thanks for both the approaches. Both return same results. What's the difference though?

Mihai Alexandru-Ionut Over a year ago

@demouser123, in the second one I used arrow functions which are features of ES6.

Mihai Alexandru-Ionut Over a year ago

@demouser123, don't forget to accept and answer in order to help other people.

JollyJoker Over a year ago

I don't understand why you used destructuring here. Do you find it easier to read than just data.filter(d => d.website == 'google').map(d => d.name) ?

CertainPerformance · Accepted Answer · 2018-05-11 07:09:34Z

1

Use reduce to push to another array based on a condition:

const data = [{"name":"Lenovo Thinkpad 41A4298","website":"google"},
{"name":"Lenovo Thinkpad 41A2222","website":"google"},
{"name":"Lenovo Thinkpad 41Awww33","website":"yahoo"},
{"name":"Lenovo Thinkpad 41A424448","website":"google"},
{"name":"Lenovo Thinkpad 41A429rr8","website":"ebay"},
{"name":"Lenovo Thinkpad 41A429ff8","website":"ebay"},
{"name":"Lenovo Thinkpad 41A429ss8","website":"rediff"},
{"name":"Lenovo Thinkpad 41A429sg8","website":"yahoo"}];
const nameArr = data.reduce((nameArr, { name, website }) => {
  if (website === 'google') nameArr.push(name);
  return nameArr;
}, []);
console.log(nameArr);

answered May 11, 2018 at 7:09

CertainPerformance

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Comments

Michael Daniels · Accepted Answer · 2018-05-11 07:35:23Z

You can simply map over the object array and IF item.website === 'google', push item.name into an array. See the working solution below...

let theJSON = [
  {"name":"Lenovo Thinkpad 41A4298","website":"google"},
  {"name":"Lenovo Thinkpad 41A2222","website":"google"},
  {"name":"Lenovo Thinkpad 41Awww33","website":"yahoo"},
  {"name":"Lenovo Thinkpad 41A424448","website":"google"},
  {"name":"Lenovo Thinkpad 41A429rr8","website":"ebay"},
  {"name":"Lenovo Thinkpad 41A429ff8","website":"ebay"},
  {"name":"Lenovo Thinkpad 41A429ss8","website":"rediff"},
  {"name":"Lenovo Thinkpad 41A429sg8","website":"yahoo"}
]

let nameArray = []

theJSON.map((item) => {
  if (item.website === 'google') {
    nameArray.push(item.name)
  }
})

console.log(nameArray)

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