function tabulateBy( collection, options, indicator ) {
	var thisArg;
	var count;
	var opts;
	var tmp;
	var len;
	var out;
	var err;
	var cb;
	var v;
	var i;
	var j;
	if ( !isCollection( collection ) ) {
		throw new TypeError( format( 'invalid argument. First argument must be a collection. Value: `%s`.', collection ) );
	}
	opts = {};
	if ( arguments.length === 2 ) {
		cb = options;
	} else {
		err = validate( opts, options );
		if ( err ) {
			throw err;
		}
		cb = indicator;
	}
	if ( !isFunction( cb ) ) {
		throw new TypeError( format( 'invalid argument. Last argument must be a function. Value: `%s`.', cb ) );
	}
	thisArg = opts.thisArg;
	count = 0;
	tmp = [];
	out = [];

	// For each collection element, determine if we've seen the element before. If not, cache a reference which points to its location in the output array; otherwise, update the running count.
	len = collection.length;
	for ( i = 0; i < len; i++ ) {
		v = cb.call( thisArg, collection[ i ], i );
		count += 1;
		j = indexOf( tmp, v );
		if ( j === -1 ) {
			tmp.push( v );
			out.push( [ v, 1, 0 ] );
		} else {
			out[ j ][ 1 ] += 1;
		}
	}
	// Compute percentages...
	len = out.length;
	for ( i = 0; i < len; i++ ) {
		out[ i ][ 2 ] = out[ i ][ 1 ] / count;
	}
	return out;
}
Generates a frequency table according to a provided function.

## Notes

-   The output 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

@param {Collection} collection - input collection
@param {Options} [options] - function options
@param {*} [options.thisArg] - execution context
@param {Function} indicator - function whose return values are used to populate the output frequency table
@throws {TypeError} first argument must be a collection
@throws {TypeError} options argument must be an object
@throws {TypeError} last argument must be a function
@throws {TypeError} must provide valid options
@returns {(Array<Array>|Array)} frequency table

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

var arr = [ 'beep', 'boop', 'foo', 'beep' ];

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