Flatten Array

Puzzle

Write a function array_flatten that takes a contents array and return a flattened array of all elements as output.

Examples

// INPUT
> var contents = [1, [2, 3, [4]], {a: 5}, ["John", [{b: ["test"]}]]];
> array_flatten(contents);

// OUTPUT
[1, 2, 3, 4, {a: 5}, "John", {b: ["test"]}];

Solution

How It Works

This solution uses recursion to complete the following steps:

1. Create an empty output array to return.
2. Loop through the contents array elements.
   • Check the type of the current element in the loop.
     • If not an array → Add element to output.
     • If an array →
       • Recursively pass element to self to get recursive_output.
       • Loop through recursive_output elements and add each to output.
3. Return output.

Code

/**
*
* Flattens an array
*
* @param {array} contents - Input array
* @return {array} output - Flattened array
*
**/
function array_flatten(contents) {

  // the output array we will return
  var output = [];
  
  // iterate over contents
  for(var i = 0; i < contents.length; i++) {
    
    // check if element is an array or not
    if(!Array.isArray(contents[i])) {

      // element is not an array - push to output array
      output.push(contents[i]);

    } else {

      // element is an array - call array_flattten on element recursively
      var recursive_output = array_flatten(contents[i]);
      
      for(var o = 0; o < recursive_output.length; o++) {
        
        output.push(recursive_output[o]);
        
      };
      
    };
    
  };
  
  // return flattened array
  return output;
  
};

Libraries

The following libraries have functions that solve this puzzle:

• Lo-Dash’s flatten function - _.flatten flattens a nested array. In addition you can choose to only flatten the first level or pass elements to a callback before flattening.