Replace element that has changed in array

Question

I have an array of attendees, 2 of them are also instructors. I want to update one of the instructors by replacing him/her and leave the remaining attendees intact in the array.

Here's an example:

    {   
      attendees: [ 
        { email: '[email protected]' },
        { email: '[email protected]' },
        { email: '[email protected]' },
        { email: '[email protected]' },
        { email: '[email protected]' } 
      ]
    }

Now I submit a new array of instructors with one of them changed:

    {
      instructors: [
        { email : '[email protected]' },
        { email : '[email protected]' }
      ]
    }

And my final result should be:

    {   
      attendees: [ 
        { email: '[email protected]' },
        { email: '[email protected]' },
        { email: '[email protected]' },
        { email: '[email protected]' },
        { email: '[email protected]' } 
      ]
    }

Where [email protected] has replaced [email protected] as the new instructor. I think I can use _.differenceBy with lodash but can't figure out how to replace the changed element in the array. Is there an elegant way to do this?

This doesn't seem to make sense. In the original set the only way to know something is an instructor is by inspecting the email. After the replacement, there's no way to know that 'test' is an instructor. Is that what you want? — Sigfried
– Sigfried, Commented Apr 7, 2016 at 12:11
Your attendee and instructor arrays would need an extra attribute for each person, like id, where they can be identified with and matched across the 2 arrays. — S.B.
– S.B., Commented Apr 7, 2016 at 12:14
Do the atteendees and instructors share the same index? Eg. attendees[0] === instructors[0]? In that case something like this jsfiddle.net/wyL19ojr ? — Pimmol
– Pimmol, Commented Apr 7, 2016 at 12:15

Oscar Gonzalez · Accepted Answer · 2016-04-07 12:28:18Z

Here is a few solutions that either 1) puts the updates in a new variable or 2) updates the attendees variable. Of course, this is pretty limited because your data doesn't have something akin to a primary key (ie: an ID field). If you do have a primary key, then you can modify these examples to check the id.

var attendees = [ 
    { email: '[email protected]' },
    { email: '[email protected]' },
    { email: '[email protected]' },
    { email: '[email protected]' },
    { email: '[email protected]' } 
]

var instructors = [
    { email : '[email protected]' },
    { email : '[email protected]' }
]

// 1) in a new variable
var updatedAttendees = attendees.map(function(item, index) {
    return instructors[index] || item;
})

// 2) In the same variable
for (var i = 0; i < attendees.length; i++) {
    if (instructors[i]) {
        attendees[i] = instructors[i];
    }
}

If you did have a primary key, it might look like this. Note that we now have two nested loops. This example is not optimized at all, but just to give you the general idea:

var attendeesWithId = [
    { id: 1, email: '[email protected]' },
    { id: 2, email: '[email protected]' },
    { id: 3, email: '[email protected]' },
    { id: 4, email: '[email protected]' },
    { id: 5, email: '[email protected]' } 
]

var updates = [
    { id: 4, email: '[email protected]' },
]

for (var j = 0; j < updates.length; j++) {
    var update = updates[j];

    for (var i = 0; i < attendeesWithId.length; i++) {
        if (update.id === attendeesWithId[i].id) {
            attendeesWithId[i] = update;
        }
    }
}

Rajshekar Reddy · Accepted Answer · 2016-04-07 12:21:53Z

0

Does this help

var initialData =  {   
      attendees: [ 
        { email: '[email protected]' },
        { email: '[email protected]' },
        { email: '[email protected]' },
        { email: '[email protected]' },
        { email: '[email protected]' } 
      ]
    }

var updateWithThis = {
      instructors: [
        { email : '[email protected]' },
        { email : '[email protected]' }
      ]
    }

for(var i=0; i< updateWithThis.instructors.length;i++){
    initialData.attendees[i] = updateWithThis.instructors[i];
}

document.write(JSON.stringify(initialData));

answered Apr 7, 2016 at 12:21

Rajshekar Reddy

19.1k4 gold badges45 silver badges64 bronze badges

Collectives™ on Stack Overflow

Replace element that has changed in array

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related