CODEWITHSUNDEEP
javascript
user13130816
user13130816

Reputation:

How to calculate the length of array objects by an id?

I have multiple array of objects with two different ids, how to calculate the length of objects based on the id. 

arr.filter(el=> {
if(el.p_id == "mobile"){
mobile_lenght = el.length}
else{
electronics_length = el.length
}

 arr =   [{id:"1", p_id:"mobile", c_code:"aaa"},
    {id:"2", p_id:"electronics", c_code:"aaa"},
    {id:"1", p_id:"mobile", c_code:"bbb"},
    {id:"2", p_id:"electronics", c_code:"bbb"}]

expected output
mobile_length = 2;
electronics_length = 2;

Upvotes: 0

Views: 527

Answers (2)

Scott Sauyet
Scott Sauyet

Reputation: 50797

You can write a generic function that counts elements matching a key you generate. Then, by passing it a function that returns an object's p_id, you can get the result you want.

const countBy = (fn) => (xs) => 
  xs .reduce ((a, x, _, __, key = fn (x)) => ({... a, [key]: (a[key] || 0) + 1}), {})

const arr = [{id:"1", p_id:"mobile", c_code:"aaa"}, {id:"2", p_id:"electronics", c_code:"aaa"}, {id:"1", p_id:"mobile", c_code:"bbb"}, {id:"2", p_id:"electronics", c_code:"bbb"}]

console .log (
  countBy (x => x .p_id) (arr)  //=> {mobile: 2, electronics: 2}
)

If you would rather this output:

{mobile_length: 2, electronics_length: 2}

then you can just call it like this instead:

countBy (x => `${x .p_id}_length`) (arr)

countBy is a general utility function that you might reuse across an application or in multiple different applications.

Upvotes: 0

Mahdi Ghajary
Mahdi Ghajary

Reputation: 3253

const arr =  [{id:"1", p_id:"mobile", c_code:"aaa"},
{id:"2", p_id:"electronics", c_code:"aaa"},
{id:"1", p_id:"mobile", c_code:"bbb"},
{id:"2", p_id:"electronics", c_code:"bbb"}]


const calc = (id) => arr.filter((el) => el.p_id  === id).length


const result = calc("mobile");

console.log(result);

Upvotes: 2

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