Retrieve the final elements of an array that share a common identifier

Question

Retrieve the final elements of an array that share a common identifier

Retrieve the latest entries from the array with identical ids:

Input:

[{id:1,name:"Java"},{id:1,name:"JavaScript"},{id:1,name:"Python"},{id:1,name:"C++"},{id:2,name:"C"},{id:2,name:"Ruby"},{id:2,name:"Php"}]

Desired Output:

[{id:1,name:"C++"},{id:2,name:"Php"}]

Attempted Solution:

array?.reverse().filter( (ele, ind) => ind === array.findIndex((elem) => elem?.id === ele?.id))

However, it resulted in the incorrect output

[{id:1,name:"Java"},{id:2,name:"C"}]

javascript arrays

Answer 1

Answer №1

To achieve this, a simple Array.reduce() can be used to create a map with the key being the id. The map is then converted into an array using Object.values():

const input = [{id:1,name:"Java"},{id:1,name:"JavaScript"},{id:1,name:"Python"},{id:1,name:"C++"},{id:2,name:"C"},{id:2,name:"Ruby"},{id:2,name:"Php"}];

const result = Object.values(input.reduce((acc, cur) => { 
    acc[cur.id] = cur;
    return acc;
}, {}))

console.log('Result:', result)

Alternatively, one could also utilize a Map and apply reduce once more:

const input = [{id:1,name:"Java"},{id:1,name:"JavaScript"},{id:1,name:"Python"},{id:1,name:"C++"},{id:2,name:"C"},{id:2,name:"Ruby"},{id:2,name:"Php"}];
const result = [...input.reduce((acc, cur) => {
    return acc.set(cur.id, cur);
}, new Map()).values()];
console.log('Result:', result);

Answer 2

To achieve this, a simple Array.reduce() can be used to create a map with the key being the id. The map is then converted into an array using Object.values():

const input = [{id:1,name:"Java"},{id:1,name:"JavaScript"},{id:1,name:"Python"},{id:1,name:"C++"},{id:2,name:"C"},{id:2,name:"Ruby"},{id:2,name:"Php"}];

const result = Object.values(input.reduce((acc, cur) => { 
    acc[cur.id] = cur;
    return acc;
}, {}))

console.log('Result:', result)

Alternatively, one could also utilize a Map and apply reduce once more:

const input = [{id:1,name:"Java"},{id:1,name:"JavaScript"},{id:1,name:"Python"},{id:1,name:"C++"},{id:2,name:"C"},{id:2,name:"Ruby"},{id:2,name:"Php"}];
const result = [...input.reduce((acc, cur) => {
    return acc.set(cur.id, cur);
}, new Map()).values()];
console.log('Result:', result);

Retrieve the final elements of an array that share a common identifier

Answer №1

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