# someBy
> Test whether a collection contains at least `n` elements which pass a test implemented by a predicate function.
## Usage
```javascript
var someBy = require( '@stdlib/utils/some-by' );
```
#### someBy( collection, n, predicate\[, thisArg ] )
Tests whether a `collection` contains at least `n` elements which pass a test implemented by a `predicate` function.
```javascript
function isNegative( value ) {
return ( value < 0 );
}
var arr = [ 1, -2, 3, 4, -1 ];
var bool = someBy( arr, 2, isNegative );
// returns true
```
Once the function finds `n` successful elements, the function **immediately** returns `true`.
```javascript
function isPositive( value ) {
if ( value < 0 ) {
throw new Error( 'should never reach this line' );
}
return ( value > 0 );
}
var arr = [ 1, 2, -3, 4 ];
var bool = someBy( arr, 2, isPositive );
// returns true
```
The invoked `function` is provided three arguments:
- `value`: collection element
- `index`: collection index
- `collection`: input collection
To set the function execution context, provide a `thisArg`.
```javascript
function sum( value ) {
this.sum += value;
this.count += 1;
return ( value < 0 );
}
var arr = [ 1, 2, 3, 4, -5 ];
var context = {
'sum': 0,
'count': 0
};
var bool = someBy( arr, 1, sum, context );
// returns true
var mean = context.sum / context.count;
// returns 1.0
```
## 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`).
- If provided an empty `collection`, the function returns `false`.
```javascript
function alwaysTrue() {
return true;
}
var bool = someBy( [], 1, alwaysTrue );
// returns false
```
- The function does **not** skip `undefined` elements.
```javascript
function log( value, index ) {
console.log( '%s: %s', index, value );
return ( value < 0 );
}
var arr = [ 1, , , 4, -1 ];
var bool = someBy( arr, 1, log );
/* =>
0: 1
1: undefined
2: undefined
3: 4
4: -1
*/
```
- The function provides limited support for dynamic collections (i.e., collections whose `length` changes during execution).
## Examples
```javascript
var randu = require( '@stdlib/random/base/randu' );
var someBy = require( '@stdlib/utils/some-by' );
function threshold( value ) {
return ( value > 0.95 );
}
var bool;
var arr;
var i;
arr = new Array( 100 );
for ( i = 0; i < arr.length; i++ ) {
arr[ i ] = randu();
}
bool = someBy( arr, 5, threshold );
// returns
```
[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