查找两个数组之间的对称差

Question

I need to find any differences between two arrays in the elements and push said elements onto a new array that is then returned in the end. I have pulled a function from this website through searching that has the intended purpose of counting the number of times an element occurs in an array and returning that. First I have concatenated the two arrays together, then applied this function (modified it to fit my problem as well as I could). I then tried to push the elements that were different (didn't occur twice) to the new array. My code of course doesn't work and I am also new to Javascript, so please be easy on me.

Below is some code of what I have tried, which doesn't pass any tests:

function diffArray(arr1, arr2) {
  var newArr = [];

  let tempArr = arr1.concat(arr2);

  function countInArray(array, what) {
    var count = 0;
    for (var i = 0; i < array.length; i++) {
        if (array[i] === what) {
            count++;
        }
    }
    if (countInArray(tempArr, tempArr[i]) < 2) {
      newArr.push(tempArr[i]);
    } 
}


  return newArr;
}

If you provide any code please try to break it down for me so that I can understand better and learn.

Answer 1

You could take a Set

The Set object lets you store unique values of any type, whether primitive values or object references.

and return the difference from left and right side.

 function getSymDifference(a, b) { return getDifference(a, b).concat(getDifference(b, a)); } function getDifference(a, b) { var setB = new Set(b); return a.filter(v => !setB.has(v)); } console.log(getSymDifference(["diorite", "andesite", "grass", "dirt", "pink wool", "dead shrub"], ["diorite", "andesite", "grass", "dirt", "dead shrub"])); // ["pink wool"] console.log(getSymDifference([1, "calf", 3, "piglet"], [7, "filly"])); // [1, "calf", 3, "piglet", 7, "filly"] console.log(getSymDifference([], ["snuffleupagus", "cookie monster", "elmo"])); console.log(getSymDifference([1, 2, 3, 5], [1, 2, 3, 4, 5])); 

A classic approach by splicing the array to prevent using already visited or searched items to use again.

 function getSymDifference(a, b) { var aa = a.slice(), bb = b.slice(), result = [], i, j; for (i = 0; i < aa.length; i++) { j = bb.indexOf(aa[i]); if (j === -1) { result.push(aa[i]); } else { bb.splice(j, 1); } } return result.concat(bb); } console.log(getSymDifference(["diorite", "andesite", "grass", "dirt", "pink wool", "dead shrub"], ["diorite", "andesite", "grass", "dirt", "dead shrub"])); // ["pink wool"] console.log(getSymDifference([1, "calf", 3, "piglet"], [7, "filly"])); // [1, "calf", 3, "piglet", 7, "filly"] console.log(getSymDifference([], ["snuffleupagus", "cookie monster", "elmo"])); console.log(getSymDifference([1, 2, 3, 5], [1, 2, 3, 4, 5])); 

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

Answer 2

To achieve expected result, use below option by making few changes to your code

1. Return count for countInArray (currently it returns undefined)

function countInArray(array, what) { var count = 0; for (var i = 0; i < array.length; i++) { if (array[i] === what) { count++; } } return count }

2. Remove calling countInArray inside countInArray method
3. Run For Loop for tempArr to compare with other each value of tempArr

for (var j = 0; j < tempArr.length; j++) { if (countInArray(tempArr, tempArr[j]) < 2) { newArr.push(tempArr[j]); } }

Working code :

 function diffArray(arr1, arr2) { let tempArr = arr1.concat(arr2); let newArr = []; function countInArray(array, what) { var count = 0; for (var i = 0; i < array.length; i++) { if (array[i] === what) { count++; } } return count } for (var j = 0; j < tempArr.length; j++) { if (countInArray(tempArr, tempArr[j]) < 2) { newArr.push(tempArr[j]); } } return newArr; } let arr1 = ["diorite", "andesite", "grass", "dirt", "pink wool", "dead shrub"] let arr2 = ["diorite", "andesite", "grass", "dirt", "dead shrub"] console.log(diffArray(arr1, arr2)) let arr3 = [1, "calf", 3, "piglet"] let arr4 = [7, "filly"] console.log(diffArray(arr3, arr4)) 

codepen - https://codepen.io/nagasai/pen/OYNdZX?editors=1010

Answer 3

reverse the second array and probably that should ease your task

Array.Reverse method: http://www.w3schools.com/jsref/jsref_reverse.asp

Answer 4

The most elegant solution I could find is stated using ES7 apparently. I'll post it below, but if someone could help me figure out how to make my initial code work, that would be appreciated.

function diffArray(arr1, arr2) {

let difference = arr1
                 .filter(x => !arr2.includes(x))
                 .concat(arr2.filter(x => !arr1.includes(x)));


  return difference;
}

Basically this filters the first array based on what the second doesn't have and concatenates on the filtered second array based on what doesn't occur in the first. So it gets both sides, not just one, hence 'symmetric'.