benjiman benjiman - 3 months ago 25
Javascript Question

Merge Array of Objects by Property using Lodash

I have two arrays of objects that represent email addresses that have a label and a value:

var original = [
{
label: 'private',
value: 'private@johndoe.com'
},
{
label: 'work',
value: 'work@johndoe.com'
}
];

var update = [
{
label: 'private',
value: 'me@johndoe.com'
},
{
label: 'school',
value: 'schol@johndoe.com'
}
];


Now I want to compare and merge the two arrays by the
label
field, so that the result would like this:

var result = [
{
label: 'private',
value: 'me@johndoe.com'
},
{
label: 'work',
value: 'work@johndoe.com'
},
{
label: 'school',
value: 'schol@johndoe.com'
}
]


How can I do this e.g. using lodash?

Answer

_.unionBy():
This method is like _.union except that it accepts iteratee which is invoked for each element of each arrays to generate the criterion by which uniqueness is computed. Result values are chosen from the first array in which the value occurs.

var original = [
  { label: 'private', value: 'private@johndoe.com' },
  { label: 'work', value: 'work@johndoe.com' }
];

var update = [
  { label: 'private', value: 'me@johndoe.com' },
  { label: 'school', value: 'schol@johndoe.com' }
];

var result = _.unionBy(update, original, "label");

console.log(result);
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.15.0/lodash.min.js"></script>