using reduce to remove item from array

Question

I need a bit of help to remove items from an array. I have a number of check boxes, each have a dynamically created data attribute. On un-checking a check box I want to remove items from an array which match item.sector value of each array item. I can't quite get it working. Any help would be appreciated.

let mapMarkers = [];

function addFilter(self) {
        const markerObject = filterObject[self.id];
        const markerID = markerObject[0]["id"];
        const dataSetSector = self.dataset.sector;
        const dataSetYear = self.dataset.year;

        if (self.checked) {
            mapMarkers.push(markerObject);
        } else {
            // data attribute SECTOR exists
            if (self.hasAttribute("data-sector")) {
                mapMarkers = mapMarkers.reduce((acc, curr) => {             
                    if (curr.sector !== dataSetSector) acc.push(curr);
                    return acc;
                });
            } 
            // data attribute YEAR exists
            else if (self.hasAttribute("data-year")) {
                mapMarkers = mapMarkers.reduce((acc, curr) => {         
                    if (curr.sector !== dataSetYear) acc.push(curr);
                    return acc;
                });
            }
        }
    }

You can use filter insetad of reduce

Artem Kolodko
– Artem Kolodko

2018-03-13 13:21:35 +00:00
Commented Mar 13, 2018 at 13:21 — Artem Kolodko
– Artem Kolodko, Commented Mar 13, 2018 at 13:21

user3297291 · Accepted Answer · 2018-03-13 15:44:05Z

6

The second argument of reduce is the initial value, i.e. the initial value of acc. Since you're calling a push method on acc, it should probably be an array.

When you omit the second argument, the first element in your array is used as the initial value. I.e.: the first call takes (mapMarkers[0], mapMarkers[1]).

To fix this issue, pass a new array to the reduce method:

mapMarkers = mapMarkers.reduce((acc, curr) => {             
  if (curr.sector !== dataSetSector) acc.push(curr);
  return acc;
}, []);
//  ^--- change

Alternatively, as suggested in the comments, you can use filter.

answered Mar 13, 2018 at 15:44

user3297291

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2 Comments

Sharper Over a year ago

Thanks for the response. This works, which is great. But when I log out mapMarkers its showing the entries that should be filtered out not ones I want to keep.

user3297291 Over a year ago

You invert the “selection” by negating your operator: change !== to ===

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