Underscore.js

Underscore.js JavaScript's utility _ belt ***
Underscore.js 中文文档

Functionally Similar - Comparing Underscore.js to LINQ
holmes2136

group by sample

var list = [ 
  { productId: 1, unitId: 19, newId: 33 },
  { productId: 1, unitId: 20, newId: 33 },
  { productId: 1, unitId: 20, newId: 13 },
  { productId: 1, unitId: 20, newId: 70 },
  { productId: 1, unitId: 21, newId: 13 },
  { productId: 1, unitId: 21, newId: 20 }  
];

var groups = _.groupBy(list, function(value){
  return value.productId + '#' + value.unitId;
});
console.dir(groups);

var data = _.map(groups, function(group){
  //console.dir(group.length);
  return {
    productId: group[0].productId,
    unitId: group[0].unitId,
    newIds: _.pluck(group, 'newId')
  };
});

var groups2 = _.groupBy(list, function(obj){
  return JSON.stringify({productId:obj.productId, unitId:obj.unitId});
});
console.dir(groups2);

var matchs = _.reject(groups2, function(group){ return group.length === 1; });
console.dir(matchs);