compare two arrays in javascript and delete the object that both arrays have

Question

I have 2 arrays:

0: {id: 2, name: "TMA"}
1: {id: 3, name: "Hibbernate"}

0: {id: 1, name: "FB.DE"}
1: {id: 2, name: "TMA"}
2: {id: 3, name: "Hibbernate"}
3: {id: 4, name: "Event.it A"}
4: {id: 5, name: "Projket 2"}
5: {id: 6, name: "Projekt 1"}

I want to compare them and delete the objects with the id 2 and 3 cause both arrays have them and thats the similarity.

This is my Code so far:

const projectListOutput = projectsOfPersonArray.filter(project => data.includes(project));
 console.log(projectListOutput);

But every time i run this projectListOutput is empty.

• Ehsan Nazeri: are both arrays sorted?
• Gerrit: When you mean bay sorted with the sort() function, then yes.
• Heretic Monkey: Which array is projectsOfPersonArray and which is data? Because if the short one is projectsOfPersonArray, then you've filtered both elements out...

Answer 1

When using includes dont compare objects, Just build data as array of strings. Remaining code is similar to what you have.

arr1 = [
 { id: 2, name: "TMA" },
 { id: 3, name: "Hibbernate" },
];
arr2 = [
 { id: 1, name: "FB.DE" },
 { id: 2, name: "TMA" },
 { id: 3, name: "Hibbernate" },
 { id: 4, name: "Event.it A" },
 { id: 5, name: "Projket 2" },
 { id: 6, name: "Projekt 1" },
];
const data = arr1.map(({ id }) => id);
const result = arr2.filter(({ id }) => !data.includes(id));
console.log(result);

Answer 2

Your data array probably does not contain the exact same object references than projectsOfPersonArray. Look at the code below:

[{ foo: 'bar' }].includes({ foo: 'bar' });
// false

Objects look equal, but they don't share the same reference (= they're not the same). It's safer to use includes with primitive values like numbers or strings. You can for example check the ids of your objects instead of the full objects.

Answer 3

You compare different objects, so every object is unique.

For filtering, you need to compare all properties or use a JSON string, if the order of properties is equal.

var exclude = [{ id: 2, name: "TMA" }, { id: 3, name: "Hibbernate" }],
 data = [{ id: 2, name: "TMA" }, { id: 3, name: "Hibbernate" }, { id: 1, name: "FB.DE" }, { id: 2, name: "TMA" }, { id: 3, name: "Hibbernate" }, { id: 4, name: "Event.it A" }, { id: 5, name: "Projket 2" }, { id: 6, name: "Projekt 1" }],
 result = data.filter(project =>
 !exclude.some(item => JSON.stringify(item) === JSON.stringify(project))
 );
console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Answer 4

You can do something similar to the next:

const source = [{
 id: 1,
 name: "FB.DE"
 },
 {
 id: 2,
 name: "TMA"
 },
 {
 id: 3,
 name: "Hibbernate"
 },
 {
 id: 4,
 name: "Event.it A"
 },
 {
 id: 5,
 name: "Projket 2"
 },
 {
 id: 6,
 name: "Projekt 1"
 }
]
const toRemove = [{
 id: 2,
 name: "TMA"
 },
 {
 id: 3,
 name: "Hibbernate"
 }
]
/**create object where keys is object "id" prop, and value is true**/
const toRemoveMap = toRemove.reduce((result, item) => ({
 ...result,
 [item.id]: true
}), {})
const result = source.filter(item => !toRemoveMap[item.id])

You can make function from it:

function removeArrayDuplicates (sourceArray, duplicatesArray, accessor) {
 const toRemoveMap = duplicatesArray.reduce((result, item) => ({
 ...result,
 [item[accessor]]: true
 }), {});
 return sourceArray.filter(item => !toRemoveMap[item[accessor]])
}
removeArrayDuplicates(source, toRemove, 'id')

Or even better, you can make it work with a function instead of just property accessor:

function removeDuplicates (sourceArray, duplicatesArray, accessor) {
 let objectSerializer = obj => obj[accessor];
 if(typeof accessor === 'function') {
 objectSerializer = accessor;
 }
 const toRemoveMap = duplicatesArray.reduce((result, item) => ({
 ...result,
 [objectSerializer(item)]: true
 }), {});
 return sourceArray.filter(item => !toRemoveMap[objectSerializer(item)])
}
removeDuplicates(source, toRemove, (obj) => JSON.stringify(obj))

Answer 5

This function will help you merge two sorted arrays

var arr1 = [
 { id: 2, name: 'TMA' },
 { id: 3, name: 'Hibbernate' },
]
var arr2 = [
 { id: 1, name: 'FB.DE' },
 { id: 2, name: 'TMA' },
 { id: 3, name: 'Hibbernate' },
 { id: 4, name: 'Event.it A' },
 { id: 5, name: 'Projket 2' },
]
function mergeArray(array1, array2) {
 var result = []
 var firstArrayLen = array1.length
 var secondArrayLen = array2.length
 var i = 0 // index for first array
 var j = 0 // index for second array
 while (i < firstArrayLen || j < secondArrayLen) {
 if (i === firstArrayLen) { // first array doesn't have any other members
 while (j < secondArrayLen) { // we copy rest members of first array as a result
 result.push(array2[j])
 j++
 }
 } else if (j === secondArrayLen) { // second array doesn't have any other members
 while (i < firstArrayLen) { // we copy the rest members of the first array to the result array
 result.push(array1[i])
 i++
 }
 } else if (array1[i].id < array2[j].id) {
 result.push(array1[i])
 i++
 } else if (array1[i].id > array2[j].id) {
 result.push(array2[j])
 j++
 } else {
 result.push(array1[i])
 i++
 j++
 }
 }
 return result
}
console.log(mergeArray(arr1,arr2));