time-to-botec/squiggle/node_modules/@stdlib/utils/do-while-each/README.md

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# doWhileEach

> While a test condition is true, invoke a function for each element in a collection.

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</section>

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## Usage

```javascript
var doWhileEach = require( '@stdlib/utils/do-while-each' );
```

#### doWhileEach( collection, fcn, predicate\[, thisArg ] )

Invokes a `function` for each element in a `collection` until either a `predicate` function returns `false` or the function has iterated over all `collection` elements. Note that the condition is evaluated **after** executing `fcn`; thus, `fcn` **always** executes at least once.

```javascript
function predicate( value ) {
    return ( value === value );
}

function log( value, index ) {
    console.log( '%s: %d', index, value );
}

var arr = [ 1, 2, 3, NaN, 4 ];

doWhileEach( arr, log, predicate );
/* =>
    0: 1
    1: 2
    2: 3
    3: NaN
*/
```

Both the `predicate` function and the `function` to apply are provided three arguments:

-   `value`: collection element
-   `index`: collection index
-   `collection`: input collection

If provided an empty `collection`, both `value` and `index` are `undefined`.

```javascript
function predicate( value ) {
    return ( value === value );
}

function log( value, index ) {
    console.log( '%s: %s', index, value );
}

var arr = [];

doWhileEach( arr, log, predicate );
/* =>
    undefined: undefined
*/
```

Basic support for dynamic collections is provided. Note, however, that index incrementation is monotonically increasing.

```javascript
function predicate( value ) {
    return ( value === value );
}

function log1( value, index, collection ) {
    console.log( '%s: %d', index, value );
    if ( index === collection.length-1 && collection.length < 10 ) {
        collection.push( index+2 );
    }
}

var arr = [ 1, 2, 3, 4 ];

doWhileEach( arr, log1, predicate );
/* =>
    0: 1
    1: 2
    2: 3
    3: 4
    4: 5
    5: 6
    6: 7
    7: 8
    8: 9
    9: 10
*/

function log2( value, index, collection ) {
    console.log( '%s: %d', index, value );
    collection.shift();
}

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

doWhileEach( arr, log2, predicate );
/* =>
    0: 1
    1: 3
*/
```

To set the function execution context for the applied function, provide a `thisArg`.

```javascript
function predicate( value ) {
    return ( value < 3 );
}

function sum( value ) {
    this.sum += value;
    this.count += 1;
}

var arr = [ 1, 2, 3, NaN, 4 ];

var context = {
    'sum': 0,
    'count': 0
};

doWhileEach( arr, sum, predicate, context );

var mean = context.sum / context.count;
// returns 2.0
```

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## Notes

-   A `collection` may be either an [`Array`][mdn-array], [`Typed Array`][mdn-typed-array], or an array-like [`Object`][mdn-object] (excluding `strings` and `functions`).

-   The function returns the input `collection`.

-   The function does **not** skip `undefined` elements.

    <!-- eslint-disable no-sparse-arrays -->

    ```javascript
    function predicate( value ) {
        return ( value === value );
    }

    function log( value, index ) {
        console.log( '%s: %s', index, value );
    }

    var arr = [ 1, , , 4 ];

    doWhileEach( arr, log, predicate );
    /* =>
        0: 1
        1: undefined
        2: undefined
        3: 4
    */
    ```

-   The function provides limited support for dynamic collections (i.e., collections whose `length` changes during execution).

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## Examples

<!-- eslint no-undef: "error" -->

```javascript
var isEven = require( '@stdlib/assert/is-even' ).isPrimitive;
var randu = require( '@stdlib/random/base/randu' );
var floor = require( '@stdlib/math/base/special/floor' );
var doWhileEach = require( '@stdlib/utils/do-while-each' );

function predicate( value ) {
    return ( value === value );
}

function log( value, index, collection ) {
    console.log( '%s: %d', index, value );
    if ( isEven( index ) ) {
        collection.shift();
    } else {
        collection.push( index+1 );
    }
}

var arr;
var j;
var i;

arr = new Array( 100 );
j = floor( randu()*arr.length );
for ( i = 0; i < arr.length; i++ ) {
    if ( i === j ) {
        arr[ i ] = NaN;
    } else {
        arr[ i ] = i;
    }
}

doWhileEach( arr, log, predicate );
```

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[mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array

[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray

[mdn-object]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object

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