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JavaScript: Combine the numbers of a given array into an array containing all combinations

JavaScript fundamental (ES6 Syntax): Exercise-9 with Solution

Write a JavaScript program to combine the numbers of a given array into an array containing all combinations.

  • Use Array.prototype.reduce() combined with Array.prototype.map() to iterate over elements and combine into an array containing all combinations.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
const powerset = arr => arr.reduce((a, v) => a.concat(a.map(r => [v].concat(r))), [[]]);
console.log(powerset([1, 2]));
console.log(powerset([1, 2, 3]));
console.log(powerset([1, 2, 3, 4]));

Sample Output:

[[],[1],[2],[2,1]]
[[],[1],[2],[2,1],[3],[3,1],[3,2],[3,2,1]]
[[],[1],[2],[2,1],[3],[3,1],[3,2],[3,2,1],[4],[4,1],[4,2],[4,2,1],[4,3],[4,3,1],[4,3,2],[4,3,2,1]]

Pictorial Presentation:

JavaScript Fundamental: Combine the numbers of a given array into an array containing all combinations

Flowchart:

flowchart: Combine the numbers of a given array into an array containing all combinations

Live Demo:

See the Pen javascript-basic-exercise-1-9 by w3resource (@w3resource) on CodePen.


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Previous: Write a JavaScript program to filter out the specified values from an specified array. Return the original array without the filtered values.
Next: Write a JavaScript program to extract out the values at the specified indexes from an specified array.

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JavaScript: Tips of the Day

How to remove a specific item from an array?

Find the index of the array element you want to remove using indexOf, and then remove that index with splice.

The splice() method changes the contents of an array by removing existing elements and/or adding new elements.

const array = [2, 5, 9];

console.log(array);

const index = array.indexOf(5);
if (index > -1) {
  array.splice(index, 1);
}

// array = [2, 9]
console.log(array);

The second parameter of splice is the number of elements to remove. Note that splice modifies the array in place and returns a new array containing the elements that have been removed.

For the reason of completeness, here are functions. The first function removes only a single occurrence (i.e. removing the first match of 5 from [2,5,9,1,5,8,5]), while the second function removes all occurrences:

function removeItemOnce(arr, value) {
  var index = arr.indexOf(value);
  if (index > -1) {
    arr.splice(index, 1);
  }
  return arr;
}

function removeItemAll(arr, value) {
  var i = 0;
  while (i < arr.length) {
    if (arr[i] === value) {
      arr.splice(i, 1);
    } else {
      ++i;
    }
  }
  return arr;
}
//Usage
console.log(removeItemOnce([2,5,9,1,5,8,5], 5))
console.log(removeItemAll([2,5,9,1,5,8,5], 5))

Ref: https://bit.ly/2N9nKRp