Javascript GroupBy function

groupby.js

function groupBy( array , f ) {
  var groups = {};
  array.forEach( function( o )
  {
    var group = JSON.stringify( f(o) );
    groups[group] = groups[group] || [];
    groups[group].push( o );
  });
  return Object.keys(groups).map( function( group )
  {
    return groups[group];
  });
}

var list = [
  {"name": "John","Average":15,"High":10,"DtmStamp":1358226000000},
  {"name": "Jane","Average":16,"High":92,"DtmStamp":1358226000000},
  {"name": "Jane","Average":17,"High":45,"DtmStamp":1358226000000},
  {"name": "John","Average":18,"High":87,"DtmStamp":1358226000000},
  {"name": "Jane","Average":15,"High":10,"DtmStamp":1358226060000},
  {"name": "John","Average":16,"High":87,"DtmStamp":1358226060000},
  {"name": "John","Average":17,"High":45,"DtmStamp":1358226060000},
  {"name": "Jane","Average":18,"High":92,"DtmStamp":1358226060000}
]

// USING IT

var sorted = groupBy(list, function(item){
  return [item.name];
});

var sorted2 = groupBy(list, function(item){
  return [item.name, item.DtmStamp];
});

console.log(sorted, sorted2)