make a left outer join in javascript

Question

From an array of objects in JavaScript (D3) I need to remove every object for which a certain attribute equals another certain attribute in another array of objects, i.e. do an anti-join, i.e. a select of left columns of left join rows with introduced nulls.

I do it with two loops but it's quite slow.

for (var i = 0; i < data1.length; i++) {
  for (var j = 0; j < data2.length; j++) {
    if (data2[j].attr3 == data1[i].attr4) {
      data2.splice(j,1);
    }
  }
}

data1.length is ~2k and data2.length is ~10k.

What is a faster method with JavaScript or jQuery or D3?

This has approximately been asked at Joins in Javascript but the solutions use external libraries.

Answer 1

You need a fast lookup for the values that exist in data1, so make a map using an object:

var map = {};
for (var i = 0; i < data1.length; i++) {
  map[data1[i].attr4] = 1;
}

Then you can loop throught the items in data2 and filter them:

var result = [];
for (i = 0; i < data2.length; i++) {
  if (!(data2[i].attr3 in map)) {
    result.push(data2[i]);
  }
}

Answer 2

Maybe not faster but more readable

const left = ['1', '2', '7']
const right = ['1', '3', '5', '9']

const result = left.filter((x) => !right.includes(x))
console.log(result)