过滤出二维数组的值

Question

I have a bidimensional array which looks like this:

[[10, 20, 30, S1]
[10, 20, 30, S1]
[10, 20, 30, S1]
[50, 70, 80, G1]
[50, 70, 80, G1]
[50, 70, 80, G1]]

I want to filter out every "non-first" occurence of the 4th value of each sub-array, like this:

[[10, 20, 30, S1]
[10, 20, 30]
[10, 20, 30]
[50, 70, 80, G1]
[50, 70, 80]
[50, 70, 80]]

How is this possible? Thanks in advance

Answer 1

You can use an object to keep track of the found values, and remove the last item from the subarrays when it was found before:

var items = {};
for (var i = 0; i < arr.length; i++) {
  var id = arr[i][arr[i].length - 1];
  if (items.hasOwnProperty(id)) {
    arr[i].pop();
  } else {
    items[id] = 1;
  }
}