Filter Array of Objects based on Values from Another Array

19 November, 2020 (2 min read)

Possible Scenario:

Let’s say we have an API response array of objects like dataSample below:

const dataSample = [
    {
      "staff": 1000,
      "name": "Apple",
      "logo_url": "biten apple",
      "down":"yes"
    },
    {
      "staff": 500,
      "name": "Microsoft",
      "logo": "squares",
      "down":"no"
    },
    {
      "staff": 4000,
      "name": "Google",
      "logo_url": "letter",
      "down":"no"
    },
    {
      "staff": 2000,
      "name": "Coca Cola",
      "logo": "letters",
      "down":"yes"
    },
  ];

We want to loop through dataSample and display the info in a tabular manner. But first, we want users to be able to select which columns they want to see. So, we present all dataSample object properties : staff, name, logo-url and down, as checkboxes. Users click on checkboxes to select which columns they want to see, and we collect their inputs into an array:

const filterArr = [“name”, “down”]

Problem:

How do we filter the objects in the dataSample array so that only the properties present in filterArray and their matching values are returned, to give us the output below?

[
    {
      "name": "Apple",
      "down": "yes"
    },
    {
      "name": "Microsoft",
      "down": "no"
    },
    {
      "name": "Google",
      "down": "no"
    },
    {
      "name": "Coca Cola",
      "down": "yes"
    },
];

Solution:

1.Using a for-in loop

const filterObjsInArr = (arr, selection) => {
    const filteredArray = [];
    arr.map((obj) => {
      const filteredObj = {};
      for (let key in obj) {
        if (selection.includes(key)) {
          filteredObj[key] = obj[key];
        };
      };
      filteredArray.push(filteredObj);
    })
    return filteredArray;
  }

The filterObjsinArr function takes in an array of objects: arr and a selection array as arguments. It maps through arr to get individual objects. For each object, it loops through each property, checking if it exists in the selection array.

2.Using Lodash’s cloneDeep() and Object.keys()

const filterObjsInArr = (arr, selection) => {
    const filteredArray = _cloneDeep(arr);
    filteredArray.map(obj => Object.keys(obj).forEach((key) => {
      if (!selection.includes(key)) {
        delete obj[key];
      }
    }))
    return filteredArray;
}

This second method is shorter in terms of lines of code. Cloning arrays in JavaScript is a bit complicated, becausearrays are stored as references. So, we use the cloneDeep method from Lodash to do that. We are cloning the original array so as not to mutate it, we need it to be intact and untouched for future filtering. We loop through each object of the cloned array, then through each property in that particular object, checking if that property exists in the selection array. If it doesn’t, we delete it.

That’s it. Go build something great or fun at least :). Say hi on twitter if you’ll love to connect or have questions. Until next time, ciao.

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