JS: Iterate over an array of objects to update object

Question

I am trying to iterate over an array of array objects to de-dupe and sort the data within each. The function onlyUnique returns unique values in an array. The problem is, it doesn't work as intended.

arr_lists = [arr_1, arr_2, arr_3, arr_4, arr_5, ...]

for (var list_obj of arr_lists) {
  list_obj = list_obj.join().split(',').filter(onlyUnique);
  list_obj.sort();
  Logger.log(list_obj);
}

The logger results show true (i.e. they are what I am looking for), but the original array is unchanged, although I think it should have been updated.

I've tried assigning the filtered array to a new array... nope. I know that I could add a thousand lines of code to achieve the results, but that seems silly.

I suspect it's something obvious.

the list_obj = ... line inside the loop reassigns list_obj to be a new array, so it is no longer a reference to one in the array. So sorting that array doesn't do anything to the original array. — Robin Zigmond
– Robin Zigmond, Commented Nov 5, 2022 at 22:52
split(',') creates a new array, and filter creates again a new array. Your code is not sorting the original array. Unrelated, but why do you do .join().split(',')? — trincot
– trincot, Commented Nov 5, 2022 at 22:54
@trincot, great question. Frankly, I don't know. I lifted the .join().split(',') code while looking for an easy way to filter to unique values in a list. I never examined the logic at the time. — J. Erik Hartel
– J. Erik Hartel, Commented Nov 10, 2022 at 15:03

Rohìt Jíndal · Accepted Answer · 2022-11-07 06:50:46Z

1

You can simply achieve it by using Set data structure to remove the duplicates and Array.sort() compare function to sort the elements in an array.

Live Demo :

const arr_lists = [[2,3,5,6], [7,2,5,3,3], [1,5,3], [4,7,4,7,3], [1,2,3]];

arr_lists.forEach((arr, index) => {
  arr_lists[index] = [...new Set(arr)].sort((a, b) => a -b);
})

console.log(arr_lists);

answered Nov 7, 2022 at 6:50

Rohìt Jíndal

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