Finding an array's objects that are not present in another array by property

Question

I'm looking for a way to find any objects in one array that are not present in another array based upon that object's property. What's the best way to do this with jQuery or underscore?

Given the following example:

"array1":[
    {"testProperty":"A"}, 
    {"testProperty":"B"}, 
    {"testProperty":"C"}
]

"array2":[
    {"testProperty":"A", "User":"Smith"}, 
    {"testProperty":"B", "User":"Smith"}, 

]

I would want to return the third object from array1 whose testProperty is "C" since it's not present in array2.

I was able to find several examples of this issue here on stackoverflow, but not when needing to do so using properties from those objects.

peregrine42 · Accepted Answer · 2016-05-10 21:25:24Z

3

I'm not sure if this counts, but if you can use lodash instead of underscore, there is a nice function called differenceBy:

var _ = require("lodash");

var array1 = [
  {"testProperty":"A"},
  {"testProperty":"B"},
  {"testProperty":"C"}
]

var array2 = [
  {"testProperty":"A", "User":"Smith"},
  {"testProperty":"B", "User":"Smith"}
]

var result = _.differenceBy(array1, array2, function(item) {
  return item["testProperty"]
});

console.log(result);

answered May 10, 2016 at 21:25

peregrine42

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Comments

Nina Scholz · Accepted Answer · 2016-05-10 21:07:44Z

2

A proposal in plain Javascript with a hash table for look-up.

var data = { "array1": [{ "testProperty": "A" }, { "testProperty": "B" }, { "testProperty": "C" }], "array2": [{ "testProperty": "A", "User": "Smith" }, { "testProperty": "B", "User": "Smith" }, ] },
    result = data.array1.filter(function (a) {
        return !this[a.testProperty];
    }, data.array2.reduce(function (r, a) {
        r[a.testProperty] = true;
        return r;
    }, Object.create(null)));

document.write('<pre>' + JSON.stringify(result, 0, 4) + '</pre>');

answered May 10, 2016 at 21:07

Nina Scholz

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2 Comments

Haymak3r Over a year ago

I prefer the jQuery approach but this works great, thanks!

royhowie Over a year ago

@Haymak3r jQuery approach? what does that even mean? none of these answers require jQuery.

Nenad Vracar · Accepted Answer · 2016-05-10 21:16:42Z

2

You can use filter with map

var a = {'array1': [{"testProperty":"A"}, {"testProperty":"B"}, {"testProperty":"C"}], 'array2': [{"testProperty":"A", "User":"Smith"}, {"testProperty":"B", "User":"Smith"}]};

var result = a.array1.filter(function(e) {
  return a.array2.map(el => { return el.testProperty}).indexOf(e.testProperty) == -1;
});

console.log(result);

answered May 10, 2016 at 21:16

Nenad Vracar

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1 Comment

royhowie Over a year ago

This is incredibly inefficient. You map over all of array2 on each iteration of filter, which is totally unnecessary.

maioman · Accepted Answer · 2016-05-10 21:25:32Z

1

here's a version in plain es6 js using filter and some method:

array1 = [
    {"testProperty":"A"}, 
    {"testProperty":"B"}, 
    {"testProperty":"C"}
];

array2 =[
    {"testProperty":"A", "User":"Smith"}, 
    {"testProperty":"B", "User":"Smith"}, 

]
  
 var r = array1.filter(x =>
    ! Object.keys(x).some(z =>
      array2.some(w =>
      Object.keys(w).some(y => y === z && w[y] === x[z])
    )));
    
    document.write(JSON.stringify(r))

answered May 10, 2016 at 21:25

maioman

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Comments

Gruff Bunny · Accepted Answer · 2016-05-13 19:51:19Z

1

You could use underscore's reject and some to get what you want:

var result = _.reject(array1, item => _.some(array2, {testProperty: item.testProperty}));

If performance is a concern and testProperty is an unique key of the objects in array2 then you could create a hash using indexBy and check for the result using has:

var hash = _.indexBy(array2, 'testProperty');
var result = _.reject(array1, item => _.has(hash, item.testProperty));

edited May 13, 2016 at 19:51

answered May 10, 2016 at 21:51

Gruff Bunny

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1 Comment

Haymak3r Over a year ago

thanks for sharing Gruff, it's great to see several different ways to implement the same functionality.

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