# randu > Create an iterator for generating uniformly distributed pseudorandom numbers between `0` and `1`.
## Usage ```javascript var iterator = require( '@stdlib/random/iter/randu' ); ``` #### iterator( \[options] ) Returns an iterator for generating uniformly distributed pseudorandom numbers between `0` and `1`. ```javascript var it = iterator(); // returns var r = it.next().value; // returns r = it.next().value; // returns r = it.next().value; // returns // ... ``` The function accepts the following `options`: - **name**: name of a supported pseudorandom number generator (PRNG), which will serve as the underlying source of pseudorandom numbers. The following generators are supported: - [`mt19937`][@stdlib/random/base/mt19937]: https://www.npmjs.com/package/@stdlib/random/tree/main/base/mt19937 - [`minstd`][@stdlib/random/base/minstd]: https://www.npmjs.com/package/@stdlib/random/tree/main/base/minstd - [`minstd-shuffle`][@stdlib/random/base/minstd-shuffle]: https://www.npmjs.com/package/@stdlib/random/tree/main/base/minstd-shuffle Default: [`'mt19937'`][@stdlib/random/base/mt19937]. - **seed**: pseudorandom number generator seed. Valid seed values vary according to the underlying PRNG. - **state**: pseudorandom number generator state. Valid state values vary according to the underlying PRNG. If provided, the function ignores the `seed` option. - **copy**: `boolean` indicating whether to copy a provided pseudorandom number generator state. Setting this option to `false` allows sharing state between two or more pseudorandom number generators. Setting this option to `true` ensures that a returned generator has exclusive control over its internal state. Default: `true`. - **iter**: number of iterations. By default, the underlying pseudorandom number generator is [`mt19937`][@stdlib/random/base/mt19937]. To use a different PRNG, set the `name` option. ```javascript var it = iterator({ 'name': 'minstd-shuffle' }); var r = it.next().value; // returns ``` To return an iterator having a specific initial state, set the iterator `state` option. ```javascript var bool; var it1; var it2; var r; var i; it1 = iterator(); // Generate pseudorandom numbers, thus progressing the generator state: for ( i = 0; i < 1000; i++ ) { r = it1.next().value; } // Create a new iterator initialized to the current state of `it1`: it2 = iterator({ 'state': it1.state }); // Test that the generated pseudorandom numbers are the same: bool = ( it1.next().value === it2.next().value ); // returns true ``` To seed the iterator, set the `seed` option. ```javascript var it1 = iterator({ 'seed': 7823 }); var r1 = it1.next().value; // returns var it2 = iterator({ 'seed': 7823 }); var r2 = it2.next().value; // returns var bool = ( r1 === r2 ); // returns true ``` To limit the number of iterations, set the `iter` option. ```javascript var it = iterator({ 'iter': 2 }); var r = it.next().value; // returns r = it.next().value; // returns r = it.next().done; // returns true ``` The returned iterator protocol-compliant object has the following properties: - **next**: function which returns an iterator protocol-compliant object containing the next iterated value (if one exists) assigned to a `value` property and a `done` property having a `boolean` value indicating whether the iterator is finished. - **return**: function which closes an iterator and returns a single (optional) argument in an iterator protocol-compliant object. - **seed**: pseudorandom number generator seed. - **seedLength**: length of generator seed. - **state**: writable property for getting and setting the generator state. - **stateLength**: length of generator state. - **byteLength**: size (in bytes) of generator state. - **PRNG**: underlying pseudorandom number generator.
## Notes - If an environment supports `Symbol.iterator`, the returned iterator is iterable. - **Warning**: the default underlying source of pseudorandom numbers may **change** in the future. If exact reproducibility is required, either explicitly specify a PRNG via the `name` option or use an underlying PRNG directly. - If PRNG state is "shared" (meaning a state array was provided during iterator creation and **not** copied) and one sets the underlying generator state to a state array having a different length, the iterator does **not** update the existing shared state and, instead, points to the newly provided state array. In order to synchronize the output of the underlying generator according to the new shared state array, the state array for **each** relevant iterator and/or PRNG must be **explicitly** set. - If PRNG state is "shared" and one sets the underlying generator state to a state array of the same length, the PRNG state is updated (along with the state of all other iterator and/or PRNGs sharing the PRNG's state array).
## Examples ```javascript var iterator = require( '@stdlib/random/iter/randu' ); var it; var r; // Create a seeded iterator for generating pseudorandom numbers: it = iterator({ 'seed': 1234, 'iter': 10 }); // Perform manual iteration... while ( true ) { r = it.next(); if ( r.done ) { break; } console.log( r.value ); } ```
[@stdlib/random/base/mt19937]: https://www.npmjs.com/package/@stdlib/random/tree/main/base/mt19937 [@stdlib/random/base/minstd]: https://www.npmjs.com/package/@stdlib/random/tree/main/base/minstd [@stdlib/random/base/minstd-shuffle]: https://www.npmjs.com/package/@stdlib/random/tree/main/base/minstd-shuffle