Update objects array from another array

Question

My main task is to update the markers on the map.

Notation:

Markers that are displayed in real-time on the map:

var markers = [
  { 'lat':10, 'lng':10, 'type':'simple'},
  { 'lat':20, 'lng':20, 'type':'simple'},
  { 'lat':40, 'lng':40, 'type':'cluster'}
]

New markers which should be on the map:

var newMarkers = [
  { 'lat':10, 'lng':10, 'type':'simple'},
  { 'lat':20, 'lng':20, 'type':'simple'},
  { 'lat':30, 'lng':30, 'type':'simple'},
  { 'lat':50, 'lng':50, 'type':'simple'}
]

Thus the problem is reduced to the subtask which I want to find solution: update the array of objects - markers from the another array of objects - newMarkers.

Thus, need to perform the following manipulation with markers array:

Remove objects from markers which are not in newMarkers (compared by three properties: lat, lng, type).
Add objects from newMarkers into markers if not exist (compared by lat, lng). If marker exist (by two properies: lat, lng) is necessary to update it, i.e. to replace by a new marker from newMarkers.

My solution ineffective since it is because it is performed for a long time on large number of markers.

Updated markers array should look like:

console.log(markers)
{ 'lat':10, 'lng':10, 'type':'simple'},
{ 'lat':20, 'lng':20, 'type':'simple'},
{ 'lat':30, 'lng':30, 'type':'simple'},
{ 'lat':50, 'lng':50, 'type':'simple'}

do we know anything about the data? is it in any sorted order? are markers unique per pairing of lat/lng? — hackerrdave
– hackerrdave, Commented Feb 10, 2017 at 1:18
Your resulting array is exactly the same as newMarkers, and I don't see how it could ever be different - you're effectively getting rid of anything not in the newMarkers array — Booboobeaker
– Booboobeaker, Commented Feb 10, 2017 at 1:19
@hackerrdave my solution, but it works slow on large markers count -pastebin.com/NnBU9Fpz — Andrei
– Andrei, Commented Feb 10, 2017 at 1:26

Andrew Willems · Accepted Answer · 2017-02-10 02:09:41Z

Just to re-state what was clarified in the comments after the question...

The 1st element in each of markers and newMarkers are equal by value but not by reference, and that matters. Thus you want all the items from newMarkers in your updated list, but if an element in newMarkers has all the same property values as an already existing element in markers then you want to keep the original element from markers.

The solution below loops through all the values in newMarkers and, if an element in markers has the same property values, the markers reference is used, otherwise the newMarkers reference is used.

const markers = [
  { 'lat':10, 'lng':10, 'type':'simple'},
  { 'lat':20, 'lng':20, 'type':'simple'},
  { 'lat':40, 'lng':40, 'type':'cluster'}
];

const newMarkers = [
  { 'lat':10, 'lng':10, 'type':'simple'},
  { 'lat':20, 'lng':20, 'type':'simple'},
  { 'lat':30, 'lng':30, 'type':'simple'},
  { 'lat':50, 'lng':50, 'type':'simple'}
];

const updatedMarkers = newMarkers.map(newMarker =>
  markers.reduce((accumulator, origMarker) => (
    (
      origMarker.lat  === newMarker.lat  &&
      origMarker.lng  === newMarker.lng  &&
      origMarker.type === newMarker.type
    ) ? origMarker : accumulator
  ), newMarker)
);

markers.map((marker, idx) => {
  console.log(`Element #${idx} from markers is present: ${!!(updatedMarkers.indexOf(marker) + 1)}`);
});
newMarkers.map((marker, idx) => {
  console.log(`Element #${idx} from newMarkers is present: ${!!(updatedMarkers.indexOf(marker) + 1)}`);
});

kalanchloe · Accepted Answer · 2017-02-10 02:01:05Z

2

If I'm understanding your problem correctly, you want to reflect changes in newMarkers in markers without simply replacing the reference on markers.

// remove (everything in markers that's not in newMarkers) from markers
_.pull(markers, ..._.difference(markers, newMarkers)); 
// push (everything in newMarkers that's not in markers) to markers
markers.push(..._.difference(newMarkers, markers));

answered Feb 10, 2017 at 2:01

kalanchloe

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