Create a function that multiplies every element in an array by 2

Question

Create a function that multiplies every element in an array by 2

This example involves some JavaScript code. Currently, I have written the following:

 var double = function (array) {
     var newArray = [];
     for(var i = 0; i<array.length; i++) {
         newArray.push(array[i]);
         newArray.push(array[i]);
     }
     return newArray;
};

...Essentially, if I input the following array:

var numbers = [1,2,3];

I would like the function to output:

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

...and so on.

javascript arrays function

Answer 1

Answer №1

Utilizing the power of reduce for a concise solution

[1,2,3].reduce(function(m,i) { return m.concat([i,i]); }, []);

Alternatively, here is the ES6 version:

[1,2,3].reduce((m,i) => m.concat([i,i]), []);

Answer 2

Utilizing the power of reduce for a concise solution

[1,2,3].reduce(function(m,i) { return m.concat([i,i]); }, []);

Alternatively, here is the ES6 version:

[1,2,3].reduce((m,i) => m.concat([i,i]), []);

Answer 3

Answer №2

Check out these different ways to achieve the same result:

function duplicateElements(array) {
   return array.concat.apply([], array.map(function (elem) { return [elem, elem] }));
}

console.log(duplicateElements([1, 2, 3]));

Here's a simpler approach that may be easier to understand:

function duplicateElements(array) {
  var newArray = [];
  array.forEach(function (elem) { newArray.push(elem, elem); });    
  return newArray;
}

console.log(duplicateElements([1,2,3]));

Lastly, here's a more modern ESNext version of achieving the same outcome:

const duplicateElements = array => array.flatMap(elem => [elem,elem]);

console.log(duplicateElements([1, 2, 3]));

Answer 4

Check out these different ways to achieve the same result:

function duplicateElements(array) {
   return array.concat.apply([], array.map(function (elem) { return [elem, elem] }));
}

console.log(duplicateElements([1, 2, 3]));

Here's a simpler approach that may be easier to understand:

function duplicateElements(array) {
  var newArray = [];
  array.forEach(function (elem) { newArray.push(elem, elem); });    
  return newArray;
}

console.log(duplicateElements([1,2,3]));

Lastly, here's a more modern ESNext version of achieving the same outcome:

const duplicateElements = array => array.flatMap(elem => [elem,elem]);

console.log(duplicateElements([1, 2, 3]));

Answer 5

Answer №3

This piece of code is untested as I am not very familiar with javascript, so there may be some syntax errors present:

var duplicateArrayItems = function (arr) {
  var res = [];
  for (var i = 0; i < arr.length; ++i) {
    res.push(arr[i]);
    res.push(arr[i]);
  }
  return res;
}

var myArr = [1, 2, 3];
document.write(duplicateArrayItems(myArr));

Initially, we define a function with a parameter named arr. Since it's a parameter, there's no need to declare it inside the function.

Then, we create an array where we will store the duplicated items. It is simply named res.

Following that, we iterate through the input array. For each item in the array, we add it twice to the result array using the push method. For instance, if the first item is 1, it will be added twice resulting in [1, 1] after one iteration.

Finally, once all elements have been processed, we return the res array.

Answer 6

This piece of code is untested as I am not very familiar with javascript, so there may be some syntax errors present:

var duplicateArrayItems = function (arr) {
  var res = [];
  for (var i = 0; i < arr.length; ++i) {
    res.push(arr[i]);
    res.push(arr[i]);
  }
  return res;
}

var myArr = [1, 2, 3];
document.write(duplicateArrayItems(myArr));

Initially, we define a function with a parameter named arr. Since it's a parameter, there's no need to declare it inside the function.

Then, we create an array where we will store the duplicated items. It is simply named res.

Following that, we iterate through the input array. For each item in the array, we add it twice to the result array using the push method. For instance, if the first item is 1, it will be added twice resulting in [1, 1] after one iteration.

Finally, once all elements have been processed, we return the res array.

Answer 7

Answer №4

A more succinct method to achieve this is as follows:

function doubleElements(arr){
   var result = []; 
   return arr.forEach(function(element){ result.push(element, element); }), result;
}

Usage example:

console.log(doubleElements([1,2,3])); // [1, 1, 2, 2, 3, 3]

If you only want to manipulate arrays containing numbers, here's a simple one-liner approach:

function doubleElements(arr){
   return arr.map(function(element){ return [element, element];}).join().split(",").map(Number);
}

Answer 8

A more succinct method to achieve this is as follows:

function doubleElements(arr){
   var result = []; 
   return arr.forEach(function(element){ result.push(element, element); }), result;
}

Usage example:

console.log(doubleElements([1,2,3])); // [1, 1, 2, 2, 3, 3]

If you only want to manipulate arrays containing numbers, here's a simple one-liner approach:

function doubleElements(arr){
   return arr.map(function(element){ return [element, element];}).join().split(",").map(Number);
}

Answer 9

Answer №5

Give this a shot:

function doubleElements(array) {
    var doubledArray = [];
    for (var i = 0; i < array.length; i++) {
        var value = array[i];
        doubledArray.push(value);
        doubledArray.push(value);
    }
    console.log(doubledArray);
}

doubleElements([4, 5, 6]);

JSFIDDLE DEMO

Answer 10

Give this a shot:

function doubleElements(array) {
    var doubledArray = [];
    for (var i = 0; i < array.length; i++) {
        var value = array[i];
        doubledArray.push(value);
        doubledArray.push(value);
    }
    console.log(doubledArray);
}

doubleElements([4, 5, 6]);

JSFIDDLE DEMO

Answer 11

Answer №6

I made a slight modification to your code snippet.

The concept is to add the current item into another array TWICE using the .push(item) method.

function duplicateArrayItems(array) {
  var newArray = [];
  for(var i = 0; i < array.length; i++) {
    newArray.push(array[i]);
    newArray.push(array[i]);
  }
  return newArray;
};

var originalArray = [4,5,6];

var duplicatedArray = duplicateArrayItems(originalArray);

alert(duplicatedArray);

Answer 12

I made a slight modification to your code snippet.

The concept is to add the current item into another array TWICE using the .push(item) method.

function duplicateArrayItems(array) {
  var newArray = [];
  for(var i = 0; i < array.length; i++) {
    newArray.push(array[i]);
    newArray.push(array[i]);
  }
  return newArray;
};

var originalArray = [4,5,6];

var duplicatedArray = duplicateArrayItems(originalArray);

alert(duplicatedArray);

Answer 13

Answer №7

Aside from the various ways to achieve this using pure Javascript as mentioned in other responses, another option is to utilize a library such as underscore or lo-dash. With these libraries, you can accomplish the task like so:

_.chain(array).map(function(x) {return [x,x]}).flatten().value()

When you use the chain function, your array is wrapped in an object which allows you to chain multiple functions together. For example, starting with [1, 2, 3], the map function will yield [[1,1],[2,2],[3,3]]. Subsequently, flatten will collapse the array into [1,1,2,2,3,3], and finally value() will unwrap it for further usage.

Answer 14

Aside from the various ways to achieve this using pure Javascript as mentioned in other responses, another option is to utilize a library such as underscore or lo-dash. With these libraries, you can accomplish the task like so:

_.chain(array).map(function(x) {return [x,x]}).flatten().value()

When you use the chain function, your array is wrapped in an object which allows you to chain multiple functions together. For example, starting with [1, 2, 3], the map function will yield [[1,1],[2,2],[3,3]]. Subsequently, flatten will collapse the array into [1,1,2,2,3,3], and finally value() will unwrap it for further usage.

Answer 15

Answer №8

This method proved to be effective for me:

When provided with an array of integers, the task is to create a new array where each value is doubled.

For instance:

[1, 2, 3] --> [2, 4, 6]

For those just starting out, utilizing the map method is recommended - it can be incredibly useful in various scenarios and is a valuable tool to understand.

function maps(integers) {
return integers.concat.apply([],
integers.map(function (n) { 
return [n*2] }));
};

Answer 16

This method proved to be effective for me:

When provided with an array of integers, the task is to create a new array where each value is doubled.

For instance:

[1, 2, 3] --> [2, 4, 6]

For those just starting out, utilizing the map method is recommended - it can be incredibly useful in various scenarios and is a valuable tool to understand.

function maps(integers) {
return integers.concat.apply([],
integers.map(function (n) { 
return [n*2] }));
};

Create a function that multiplies every element in an array by 2

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

Answer №7

Answer №8

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