Filtering array of objects with arrays based on nested value

Question

I am trying to filter an array, based on some nested object. I prepared some Fiddle

Input array looks like this:

let arrayOfElements = 
    [
        {
           "name": "a",
           "subElements": 
           [
             {"surname": 1},
             {"surname": 2}
           ]
        },
        {
           "name": "b",
           "subElements": 
           [
             {"surname": 3},
             {"surname": 1}
           ]
        },
        {
           "name": "c",
           "subElements": 
           [
             {"surname": 2},
             {"surname": 5}
           ]
        }
    ];

I want the output for this case, to look like this:

let filteredArray = 
    [
        {
          "name": "a",
          "subElements": 
          [
            {"surname": 1}
          ]
        },
        {
          "name": "b",
          "subElements": 
          [
            {"surname": 1}
          ]
        }
];

I am using this formula to do that:

let filteredArray = arrayOfElements.filter((element) => element.subElements.some((subElement) => subElement.surname === 1));

Output is almost good, but it returns objects with all objects with surnames (better check that fiddle :D), instead of cutting them away. How can i improve the filtering ?

Answer 1

After you call filter, you need to pipe the results to map, like this:

let filteredArray = arrayOfElements
  .filter((element) => 
    element.subElements.some((subElement) => subElement.surname === 1))
  .map(element => {
    let newElt = Object.assign({}, element); // copies element
    return newElt.subElements.filter(subElement => subElement.surname === '1');
  });

I am assuming here that you don't want to manipulate the original array. So, I am using Object.assign.