Skip to content

README.md

Latest commit

 

History

History
206 lines (130 loc) · 5.58 KB

README.md

File metadata and controls

206 lines (130 loc) · 5.58 KB

tabulateBy

Generate a frequency table according to an indicator function.

Usage

var tabulateBy = require( '@stdlib/utils/tabulate-by' );

tabulateBy( collection[, options,] indicator )

Generates a frequency table according to an indicator function, i.e., a function which specifies how to categorize an element in the input collection.

function indicator( v ) {
    return v[ 0 ];
}
var arr = [ 'beep', 'boop', 'foo', 'beep' ];

var out = tabulateBy( arr, indicator );
// returns [ [ 'b', 3, 0.75 ], [ 'f', 1, 0.25 ] ]

An indicator function is provided two arguments:

  • value: collection element.
  • index: collection index.
function indicator( v, i ) {
    console.log( '%d: %s', i, v );
    return v[ 0 ];
}
var arr = [ 'beep', 'boop', 'foo', 'bar' ];

var out = tabulateBy( arr, indicator );
// returns [ [ 'b', 3, 0.75 ], [ 'f', 1, 0.25 ] ]

The function accepts the following options:

  • thisArg: execution context.

To set the indicator execution context, provide a thisArg.

function indicator( v ) {
    this.count += 1;
    return v[ 0 ];
}
var context = {
    'count': 0
};
var opts = {
    'thisArg': context
};
var arr = [ 'beep', 'boop', 'foo', 'bar' ];

var out = tabulateBy( arr, opts, indicator );
// returns [ [ 'b', 3, 0.75 ], [ 'f', 1, 0.25 ] ]

console.log( context.count );
// => 4

The returned frequency table is an array of arrays. Each sub-array corresponds to a unique value in the input collection and is structured as follows:

  • 0: unique value.
  • 1: value count.
  • 2: frequency percentage.

Notes

  • A collection may be either an Array, Typed Array, or an array-like Object (excluding strings and functions).

Examples

var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var take = require( '@stdlib/array/take' );
var tabulateBy = require( '@stdlib/utils/tabulate-by' );

var vals;
var indices;
var arr;
var out;

function indicator( value ) {
    return value[ 0 ];
}

vals = [ 'beep', 'boop', 'foo', 'bar', 'woot', 'woot' ];

// Generate a list of random indices:
indices = discreteUniform( 100, 0, vals.length - 1 );

// Create a random collection by picking elements at the generated indices:
arr = take( vals, indices );

// Generate a frequency table:
out = tabulateBy( arr, indicator );
console.log( out );

See Also