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Lodash _.flatMapDeep



The lodash _.flatMapDeep method is a useful function that helps developers flatten and map complex nested data structures efficiently. This method works by taking an array of elements and applying a mapping function to each element in the array. The returned values are then flattened recursively into a single array, thereby joining all the nested arrays into one.


.flatMapDeep(collection, [iteratee=.identity])


The _.flatMapDeep method takes two arguments:

  1. Collection (Array or Object): This parameter represents the collection to iterate over.

  2. Iteratee (Function): This parameter represents the function that is invoked per iteration.


The _.flatMapDeep method returns a new array of flattened values.


Consider the following example where we have a nested array of arrays:

const arr = [1, [2, [3, [4]], 5]];

Now, if we want to flatten this array, we can use the lodash _.flatMapDeep method as follows:

const flattenedArray = _.flatMapDeep(arr);
// Output: [1, 2, 3, 4, 5]

In the above example, _.flatMapDeep takes the nested array and returns a flattened array of elements.

Additionally, in other examples, you can use the _.flatMapDeep method to iterate over an object:

const obj = {
  name: 'John',
  age: 25,
  favorites: {
    color: 'blue',
    food: 'pizza'

const flattenedArray = _.flatMapDeep(obj, (value) => {
  return typeof value === 'object' ? Object.values(value) : value;

// Output: ["John", 25, "blue", "pizza"]

In the above example, _.flatMapDeep iterates over each property of the object and checks if the value is an object. If it's an object, it converts the values into an array and returns them. If not, it returns the value.


The lodash _.flatMapDeep method is an efficient way to flatten and map complex nested data structures. It's a powerful tool in the toolbox of developers who work with large amounts of data and need to manipulate complex data structures efficiently.