# Function map Create a new matrix or array with the results of a callback function executed on each entry of a given matrix/array. For each entry of the input, the callback is invoked with three arguments: the value of the entry, the index at which that entry occurs, and the full matrix/array being traversed. Note that because the matrix/array might be multidimensional, the "index" argument is always an array of numbers giving the index in each dimension. This is true even for vectors: the "index" argument is an array of length 1, rather than simply a number. ## Syntax ```js math.map(x, callback) ``` ### Parameters Parameter | Type | Description --------- | ---- | ----------- `x` | Matrix | Array | The input to iterate on. `callback` | Function | The function to call (as described above) on each entry of the input ### Returns Type | Description ---- | ----------- Matrix | array | Transformed map of x; always has the same type and shape as x ### Throws Type | Description ---- | ----------- ## Examples ```js math.map([1, 2, 3], function(value) { return value * value }) // returns [1, 4, 9] // The calling convention for the callback can cause subtleties: math.map([1, 2, 3], math.format) // throws TypeError: map attempted to call 'format(1,[0])' but argument 2 of type Array does not match expected type number or function or Object or string or boolean // [This happens because `format` _can_ take a second argument, // but its semantics don't match that of the 2nd argument `map` provides] // To avoid this error, use a function that takes exactly the // desired arguments: math.map([1, 2, 3], x => math.format(x)) // returns ['1', '2', '3'] ``` ## See also [filter](filter.md), [forEach](forEach.md), [sort](sort.md)