Group element values according to an indicator function.
var groupValuesBy = require( '@stdlib/array/base/group-values-by' );Groups element values according to an indicator function.
function indicator( v ) {
return v[ 0 ];
}
var x = [ 'beep', 'boop', 'foo', 'bar' ];
var out = groupValuesBy( x, indicator );
// returns { 'b': [ 'beep', 'boop', 'bar' ], 'f': [ 'foo' ] }An indicator function is provided the following arguments:
- value: current array element.
- index: current array element index.
- arr: input array.
To set the indicator function execution context, provide a thisArg.
function indicator( v ) {
this.count += 1;
return v[ 0 ];
}
var x = [ 'beep', 'boop', 'foo', 'bar' ];
var context = {
'count': 0
};
var out = groupValuesBy( x, indicator, context );
// returns { 'b': [ 'beep', 'boop', 'bar' ], 'f': [ 'foo' ] }
var cnt = context.count;
// returns 4-
The value returned by an
indicatorfunction should be a value which can be serialized as an object key. As a counterexample,function indicator( v ) { return {}; } var x = [ 'beep', 'boop', 'foo', 'bar' ]; var out = groupValuesBy( x, indicator ); // returns { '[object Object]': [ 'beep', 'boop', 'foo', 'bar' ] }
while each group identifier is unique, all input array elements resolve to the same group because each group identifier serializes to the same string.
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var take = require( '@stdlib/array/base/take-indexed' );
var groupValuesBy = require( '@stdlib/array/base/group-values-by' );
function indicator( v ) {
// Use the first letter of each element to define groups:
return v[ 0 ];
}
// Define an initial array of values:
var values = [ 'beep', 'boop', 'foo', 'bar', 'woot', 'woot' ];
// Sample from the initial array to generate a random collection:
var indices = discreteUniform( 100, 0, values.length-1, {
'dtype': 'generic'
});
var x = take( values, indices );
// returns [...]
// Group the values:
var out = groupValuesBy( x, indicator );
// returns {...}
console.log( out );