lodash sort an array of objects by a property which has an array of objects

Question

I have a an object. I am able to sort the items by using lodash's _.orderBy(). However, in one of the scenario I have to sort by subject, which is an array of objects. Items inside the subject array are already sorted based on the name.

As subject is an array of the objects, I need to consider the first item for sorting.

[
  {
    "id": "1",
    "name": "peter",
    "subject": [
      {
        "id": "1",
        "name": "maths"
      },
      {
        "id": "2",
        "name": "social"
      }
    ]
  },
  {
    "id": "2",
    "name": "david",
    "subject": [
      {
        "id": "2",
        "name": "physics"
      },
      {
        "id": "3",
        "name": "science"
      }
    ]
  },
  {
    "id": "3",
    "name": "Justin",
    "subject": [
    ]
  }
]

Ori Drori · Accepted Answer · 2019-07-03 16:13:11Z

1

You can use _.get() to extract the name (or id) of the 1st item in subjects. If no item exists, _.get() will return undefined, which can be replaced with a default value. In this case, we don't want to use an empty string as a default value, since the order would change. Instead I'm checking if the value is a string, if it is I use lower case on it, if not I return it as is.

const arr = [{"id":"1","name":"peter","subject":[{"id":"1","name":"maths"},{"id":"2","name":"social"}]},{"id":"2","name":"david","subject":[{"id":"2","name":"physics"},{"id":"3","name":"science"}]},{"id":"3","name":"Justin","subject":[]}]

const result = _.orderBy(arr, o => {
  const name = _.get(o, 'subject[0].name')
  
  return _.isString(name) ? name.toLowerCase() : name
})

console.log(result)

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.js"></script>

edited Jul 3, 2019 at 16:13

answered Jul 2, 2019 at 21:25

Ori Drori

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2 Comments

indra257 Over a year ago

Thanks for the code snippet. It worked great. But I always use .tolowercase() in my orderBy just to make sure it is not case sensitive. So when I apply .tolowercase to above the code, I am getting an error because one of the item doesn't have any subjects. const result = _.orderBy(arr, o => _.get(o, 'subject[0].name').toLowercase())

Ori Drori Over a year ago

See update. Although we can use _.get() default value and set an empty string, this will change the sort order. The solution is to check if the name is a string, if it does set it to lower case, and if not return it as is.

Cody Caughlan · Accepted Answer · 2019-07-02 21:26:16Z

0

Use _.sortBy with a comparison/sorting function argument. Your function itself can look into the receiving arguments subject key (I think its the subject you want to compare?)

answered Jul 2, 2019 at 21:26

Cody Caughlan

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Comments

Akrion · Accepted Answer · 2019-07-02 22:43:34Z

0

Since you have the question also tagged with ES6 here is an JS only solution via Array.sort:

let arr = [ { "id": "1", "name": "peter", "subject": [ { "id": "1", "name": "maths" }, { "id": "2", "name": "social" } ] }, { "id": "2", "name": "david", "subject": [ { "id": "2", "name": "physics" }, { "id": "3", "name": "science" } ] }, { "id": "3", "name": "Justin", "subject": [] }, ] 

const result = arr.sort((a,b) => 
  a.subject.length && b.subject.length 
   ? a.subject[0].name.localeCompare(b.subject[0].name) 
   : a.subject.length ? -1 : 1)

console.log(result)

answered Jul 2, 2019 at 22:43

Akrion

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