time-to-botec

README.md (6167B)

---

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 # groupOwn
 
 > Group an object's **own** property values according to an indicator function.
 
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 <section class="intro">
 
 </section>
 
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 <!-- Package usage documentation. -->
 
 <section class="usage">
 
 ## Usage
 
 ```javascript
 var groupOwn = require( '@stdlib/utils/group-own' );
 ```
 
 #### groupOwn( obj, \[options,] indicator )
 
 Groups an object's **own** property values according to an `indicator` function, which specifies which group a value in the input `object` belongs to.
 
 ```javascript
 function indicator( v ) {
     return v[ 0 ];
 }
 var obj = {
     'a': 'beep',
     'b': 'boop',
     'c': 'foo',
     'd': 'bar'
 };
 
 var out = groupOwn( obj, indicator );
 // e.g., returns { 'b': [ 'beep', 'boop', 'bar' ], 'f': [ 'foo' ] }
 ```
 
 An `indicator` function is provided two arguments:
 
 -   `value`: object value
 -   `key`: object index
 
 ```javascript
 function indicator( v, k ) {
     console.log( '%s: %s', k, v );
     return v[ 0 ];
 }
 var obj = {
     'a': 'beep',
     'b': 'boop',
     'c': 'foo',
     'd': 'bar'
 };
 
 var out = groupOwn( obj, indicator );
 // e.g., returns { 'b': [ 'beep', 'boop', 'bar' ], 'f': [ 'foo' ] }
 ```
 
 The function accepts the following `options`:
 
 -   `returns`: specifies the output format. If the option equals `'values'`, the function outputs values. If the option equals `'keys'`, the function outputs keys. If the option equals `'*'`, the function outputs both keys and values. Default: `'values'`.
 -   `thisArg`: execution context.
 
 By default, the function returns object values. To return object keys, set the `returns` option to `'keys'`.
 
 ```javascript
 function indicator( v ) {
     return v[ 0 ];
 }
 var obj = {
     'a': 'beep',
     'b': 'boop',
     'c': 'foo',
     'd': 'bar'
 };
 
 var opts = {
     'returns': 'keys'
 };
 var out = groupOwn( obj, opts, indicator );
 // e.g., returns { 'b': [ 'a', 'b', 'd' ], 'f': [ 'c' ] }
 ```
 
 To return key-value pairs, set the `returns` option to `'*'`.
 
 ```javascript
 function indicator( v ) {
     return v[ 0 ];
 }
 var obj = {
     'a': 'beep',
     'b': 'boop',
     'c': 'foo',
     'd': 'bar'
 };
 
 var opts = {
     'returns': '*'
 };
 var out = groupOwn( obj, opts, indicator );
 // e.g., returns { 'b': [ [ 'a', 'beep' ], [ 'b', 'boop ], [ 'd', 'bar' ] ], 'f': [ [ 'c', 'foo' ] ] }
 ```
 
 To set the `indicator` execution context, provide a `thisArg`.
 
 ```javascript
 function indicator( v ) {
     this.count += 1;
     return v[ 0 ];
 }
 var context = {
     'count': 0
 };
 var opts = {
     'thisArg': context
 };
 var obj = {
     'a': 'beep',
     'b': 'boop',
     'c': 'foo',
     'd': 'bar'
 };
 var out = groupOwn( obj, opts, indicator );
 // e.g., returns { 'b': [ 'beep', 'boop', 'bar' ], 'f': [ 'foo' ] }
 
 console.log( context.count );
 // => 4
 ```
 
 </section>
 
 <!-- /.usage -->
 
 <!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
 
 <section class="notes">
 
 ## Notes
 
 -   Iteration order is **not** guaranteed, as `object` key enumeration is not specified according to the [ECMAScript specification][ecma-262-for-in]. In practice, however, most engines use insertion order to sort an `object`'s keys, thus allowing for deterministic iteration.
 
 -   Because iteration order is **not** guaranteed, result order is **not** guaranteed.
 
 -   The function determines the list of own enumerable properties **before** invoking the provided function. Hence, any modifications made to the input `object` **after** calling this function (such as adding and removing properties) will **not** affect the list of visited properties.
 
 -   The value returned by an `indicator` function should be a value which can be serialized as an `object` key. As a counterexample,
 
     ```javascript
     function indicator( v ) {
         return {};
     }
     var obj = {
         'a': 'beep',
         'b': 'boop',
         'c': 'foo',
         'd': 'bar'
     };
     var out = groupOwn( obj, indicator );
     // e.g., returns { '[object Object]': [ 'beep', 'boop', 'foo', 'bar' ] }
     ```
 
     while each group identifier is unique, all object values resolve to the same group because each group identifier serializes to the same `string`.
 
 </section>
 
 <!-- /.notes -->
 
 <!-- Package usage examples. -->
 
 <section class="examples">
 
 ## Examples
 
 <!-- eslint no-undef: "error" -->
 
 ```javascript
 var randu = require( '@stdlib/random/base/randu' );
 var fromCodePoint = require( '@stdlib/string/from-code-point' );
 var groupOwn = require( '@stdlib/utils/group-own' );
 
 var key;
 var obj;
 var out;
 var i;
 
 // Generate a random object...
 obj = {};
 for ( i = 0; i < 100; i++ ) {
     key = fromCodePoint( 97+i );
     obj[ key ] = randu();
 }
 
 function indicator( v ) {
     if ( v < 0.5 ) {
         return 'low';
     }
     return 'high';
 }
 
 // Compute the groups:
 out = groupOwn( obj, indicator );
 console.log( out );
 ```
 
 </section>
 
 <!-- /.examples -->
 
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 </section>
 
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 <section class="links">
 
 [ecma-262-for-in]: http://www.ecma-international.org/ecma-262/5.1/#sec-12.6.4
 
 </section>
 
 <!-- /.links -->