Remove number from array and shift the remaining ones JavaScript

In this problem statement, our task is to write a function to remove numbers from an array and shift the remaining elements using JavaScript. We'll explore multiple approaches including the filter method, for loops, and in-place modification to achieve this functionality.

Understanding the Problem

We need to create a function that removes all occurrences of a given number from an array and shifts the remaining items to fill the gaps. For example, given array [1, 2, 3, 4, 2, 5] and number 2, the result would be [1, 3, 4, 5] with all instances of 2 removed and elements shifted left.

Using filter() Method

The filter() method creates a new array with elements that pass a test condition:

const arrayOfNumbers = [12, 22, 35, 44, 52, 35, 68];
const numberToRemove = 35;

const arrayWithoutNum = arrayOfNumbers.filter(function (number) {
   return number !== numberToRemove;
});

console.log("Original Array:", arrayOfNumbers);
console.log("Array after removal:", arrayWithoutNum);

Original Array: [12, 22, 35, 44, 52, 35, 68]
Array after removal: [12, 22, 44, 52, 68]

Using for Loop

Manual iteration with a for loop gives more control over the process:

const arrayOfNumbers = [12, 22, 35, 44, 52, 35, 68];
const numberToRemove = 35;
const arrayWithoutNum = [];

for (let i = 0; i < arrayOfNumbers.length; i++) {
   if (arrayOfNumbers[i] !== numberToRemove) {
      arrayWithoutNum.push(arrayOfNumbers[i]);
   }
}

console.log("Original array:", arrayOfNumbers);
console.log("Array after removal:", arrayWithoutNum);

Original array: [12, 22, 35, 44, 52, 35, 68]
Array after removal: [12, 22, 44, 52, 68]

In-Place Modification

For memory efficiency, we can modify the original array in-place:

function removeNumberInPlace(arr, numToRemove) {
   let writeIndex = 0;
   
   for (let readIndex = 0; readIndex < arr.length; readIndex++) {
      if (arr[readIndex] !== numToRemove) {
         arr[writeIndex] = arr[readIndex];
         writeIndex++;
      }
   }
   
   // Trim array to new length
   arr.length = writeIndex;
   return arr;
}

const numbers = [12, 22, 35, 44, 52, 35, 68];
console.log("Before:", numbers);
removeNumberInPlace(numbers, 35);
console.log("After in-place removal:", numbers);

Before: [12, 22, 35, 44, 52, 35, 68]
After in-place removal: [12, 22, 44, 52, 68]

Comparison

Conclusion

The filter() method provides the cleanest solution for removing numbers from an array. Use in-place modification when memory efficiency is critical, and for loops when you need maximum control over the process.