function unzip( arr, idx ) {
	var numVals;
	var len;
	var out;
	var tmp;
	var i;
	var j;
	var k;

	if ( !isArray( arr ) ) {
		throw new TypeError( 'invalid argument. Must provide a zipped array.' );
	}
	len = arr.length;
	for ( i = 0; i < len; i++ ) {
		if ( !isArray( arr[i] ) ) {
			throw new TypeError( 'invalid argument. Array must only contain arrays.' );
		}
	}
	// Assume that the first tuple is representative of all tuples...
	numVals = arr[ 0 ].length;
	if ( arguments.length > 1 ) {
		if ( !isArray( idx ) ) {
			throw new TypeError( 'invalid argument. Indices must be specified as an array.' );
		}
		for ( i = 0; i < idx.length; i++ ) {
			k = idx[ i ];
			if ( !isInteger( k ) ) {
				throw new TypeError( 'invalid argument. All indices must be integers.' );
			}
			if ( k < 0 || k > numVals ) {
				throw new Error( 'invalid argument. Must provide valid indices (i.e., must be a nonnegative integer less than or equal to the tuple length).' );
			}
		}
		numVals = idx.length;
	} else {
		idx = [];
		for ( i = 0; i < numVals; i++ ) {
			idx.push( i );
		}
	}
	out = [];
	for ( j = 0; j < numVals; j++ ) {
		tmp = [];
		k = idx[ j ];
		for ( i = 0; i < len; i++ ) {
			tmp.push( arr[ i ][ k ] );
		}
		out.push( tmp );
	}
	return out;
}
Unzips a zipped array (i.e., a nested array of tuples).

@param {Array} arr - zipped array
@param {Array} [idx] - array of indices specifying which tuple elements to unzip
@throws {TypeError} first argument must be a zipped array
@throws {TypeError} second argument must be an array of integer indices
@throws {Error} indices must be on the interval from zero to the tuple length
@returns {Array} array of unzipped arrays

@example
var arr = [ [ 1, 'a', 3 ], [ 2, 'b', 4 ] ];

var out = unzip( arr );
// returns [ [ 1, 2 ], [ 'a', 'b' ], [ 3, 4 ] ]

@example
var arr = [ [ 1, 'a', 3 ], [ 2, 'b', 4 ] ];

var out = unzip( arr, [ 0, 2 ] );
// returns [ [ 1, 2 ], [ 3, 4 ] ]