如何从二维数组中删除元素

Question

I have a 2d array like this:

var rawData = [
    [1325347200000, 60], [1328025600000, 100], [1330531200000, 15], [1333209600000, 50]
];

//MEMORY
mem.push([
    iteration,
    memory.usage / (1024*1024)
]);

that keeps growing. I want to limit the size to 20, so I want to remove the oldest element in the array. I tried this but remove one element but keeps growing

//Remove first
if(iteration % 20 === 0) {
    rawData = rawData.splice(1);
}

Answer 1

I would implement an own push method that leftshifts the whole array:

class LimitedArray extends Array {
  constructor(max, ...args){
     super(max);
     this.push(...args);
  }

  push(...els){
    for(let i = els.length; i < this.length; i++)
          this[i - els.length] = this[i];
    for(let i = 0; i < els.length; i++)
       this[i + this.length - els.length] = els[i];
  }
}

So one can do:

 const cache = new LimitedArray(20);
 cache.push(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21);
cache.push(22);

---

If you really want to do that "inline", you can do:

 mem.push([1,2]);
 if(mem.length > 20) mem.shift();

---

Or if its not accurate and mem might be longer than 21:

mem.push([1,2],[3,4]);
if(mem.length > 20) mem.splice(0, mem.length - 20);

As suggested in the comments already, that can be simplified to:

mem.push([1,2], [3,4]);
mem = mem.slice(-20);

however that might be less performant and less memory efficient.