希望这会有所帮助：

var arr = [
  {a: "b"},
  {a: "b"},
  {a: "c"},
  {a: "c"}
];

var arr2 = [];
var arr3 = [];

Object.keys(arr).forEach(key => {
    Object.keys(arr[key]).forEach(keyx => {
        if (!(arr[key][keyx] in arr2)) {
            arr2[arr[key][keyx]] = [];
        }
        var k = keyx;
        var x = 1;
        var i = true;
        while (i === true) {
            if (!(k in arr2[arr[key][keyx]])) {
                i = false;
                arr2[arr[key][keyx]][k] = arr[key][keyx];
            }
            k = keyx + x;
            x++;
        }
    })
});

for (i in arr2) {
    arr3.push(arr2[i]);
}

//arr3 is the expected array