var wang = [{g: 1, c:"aa"}, {g: 1, c: "bb"}, {g: 4, c: "cc"}, {g: 2, c: "dd"}, {g: 2, c:"ee"}, 
        {g: 2, c: "ff"}, {g: 3, c: "gg"}];

        var xxx = wang.map(function(item) {
            return item.g;
        });
        console.log("xxx: ",xxx);

        var yyy = [];
        xxx.forEach(function(item) {
            if (yyy.length > 0) {
                if (yyy.indexOf(item) > -1) {
                    return 
                } else {
                    yyy.push(item);
                }
            } else {
                yyy.push(item);
            }
        });
        console.log("yyy: ",yyy);

        var zzz = [];
        yyy.forEach(function(item) {
            zzz.push(wang.filter(function(apItem) {
                return apItem.g == item;
            }));
        })
        console.log("zzz: ",zzz);

简化附带说明版本：

 var wang = [{g: 1, c:"aa"}, {g: 1, c: "bb"}, {g: 4, c: "cc"}, {g: 2, c: "dd"}, {g: 2, c:"ee"}, 
        {g: 2, c: "ff"}, {g: 3, c: "gg"}];

        //提取所有g值得数组
        var xxx = wang.map(function(item) {
            return item.g;
        });
        console.log("xxx: ",xxx);

        //返回去重之后的数组。
        var yyy = [];
        xxx.forEach(function(item) {
            !(yyy.indexOf(item) > -1) && yyy.push(item)
        });
        console.log("yyy: ",yyy);

        var zzz = [];
        yyy.forEach(function(item) {
            //每次循环都会分组，分好的组分别push到zzz
            zzz.push(wang.filter(function(apItem) {
                return apItem.g == item;
            }));
        });

console.log("zzz: ",zzz);