JavaScript. How to Compare Input Arrays

Question

I'm stuck with this problem for 3 days now... Someone please help me.

Challenge 5
Construct a function intersection that compares input arrays and returns a new array with elements found in all of the inputs.

function intersection(arrayOfArrays) {

}

console.log(intersection([[5, 10, 15, 20], [15, 88, 1, 5, 7], [1, 10, 15, 5, 20]]));

// should log: [5, 15]

Answer 1

Reduce the arrays to a Map of counts, with the value as key. Spread the Map to entries . Use Array.filter() on the Map's entries to remove all entries, which value is not equal to the arrayOfArrays lenth. Extract the original number from the entries using Array.map() :

 function intersection(arrayOfArrays) { return [...arrayOfArrays.reduce((r, s) => { s.forEach((n) => r.set(n, (r.get(n) || 0) + 1)); return r; }, new Map())] .filter(([k, v]) => v === arrayOfArrays.length) .map(([k]) => k); } console.log(intersection([[5, 10, 15, 20], [15, 88, 1, 5, 7], [1, 10, 15, 5, 20]])); 

Answer 2

You could reduce the array by filtering with just checking if the other array contains the value.

This works for arrays with unique values.

Array#reduce :

If no initialValue is provided, then accumulator will be equal to the first value in the array, and currentValue will be equal to the second.

The callback

 a.filter(v => b.includes(v)) 

filters array a . If the array b includes the value of a , then this value v is included in the accumulator for the next iteration or as final result.

  accumulator currentValue new accumulator ab result -------------------- -------------------- -------------------- [ 5, 10, 15, 20] [15, 88, 1, 5, 7] [ 5, 15] [ 5, 15] [ 1, 10, 15, 5, 20] [ 5, 15] 

 function intersection(arrayOfArrays) { return arrayOfArrays.reduce((a, b) => a.filter(v => b.includes(v))); } console.log(intersection([[5, 10, 15, 20], [15, 88, 1, 5, 7], [1, 10, 15, 5, 20]])); 

Answer 3

First try to find out the intersection of two arrays which is the base problem . Then try to build up for variable number of arrays passed as arguments for intersection. You can use reduce() for doing that.

 function intersectionOfTwoArrays(arr1, arr2) { return arr1.filter(x => arr2.some(y => y === x)); } function intersection(...arrayOfArrays) { return arrayOfArrays .reduce((a, b) => intersectionOfTwoArrays(a, b)); } intersection( [5, 10, 15, 20], [15, 88, 1, 5, 7], [1, 10, 15, 5, 20] ); 

Answer 4

You can go through the first array in the array of arrays and check which of its value is present in all the other arrays.

Here is an example:

 function intersection(input) { let firstArray = input[0]; let restOfArrays = input.splice(1); return firstArray.filter(v => restOfArrays.every(arr => arr.includes(v))); } const input = [[5, 10, 15, 20], [15, 88, 1, 5, 7], [1, 10, 15, 5, 20]]; const result = intersection(input); console.log(result); 

Answer 5

I think you want the common elements. Let me show you how:

var Array1 = [5, 10, 15, 20]
var Array2 = [15, 88, 1, 5, 7]
var Array3 = [1, 10, 15, 5, 20]
var found = []
var Final = []
var c = 1;e = 1;
for (i = 1;i<=Array1.length;i++){
    for (k = 1;k<=Array2.length;i++){
        if (Array1[i] == Array2[k]){
            Found[c] = Array[i];
            c++;
        }
    }
}
for (n = 1;n <= Found.length ; n++){
    for (m = 1;m <= Array3.length ; n++){
        if (Found[n] == Array3[m]){
            Final[e] = Found[n]
            e++; 
        }
    }
}
//the Array Final Contains 5 , 15

Answer 6

Works with even if there is duplicate in same array.. like in my example added 5 twice in arrayEle[1];

var arrayEle = [[5, 10, 15, 20], [15, 88, 1, 5, 5], [1, 10, 15, 5, 20]]
var startIndex = 1;
var newArray = [];
for (var x = 0; x < arrayEle[0].length; x++) {
  var temVal = 1;
  var value;
  for (var y = 1; y < arrayEle.length; y++) {
    for (var z = 0; z < arrayEle[y].length; z++) {
      if (arrayEle[y][z] == arrayEle[0][x]) {
        temVal++;
        value = arrayEle[y][z];
        break;
      }
    }
  }
  if (temVal == arrayEle.length) {
    newArray.push(value);
    console.log(value);
  }
}
console.log(newArray);


//log: [5, 15]