Lodash map value from nested object in array of objects

Question

I am trying to use a lodash's map function to extract a value from a nested object in an array of objects and store it in a new key. But always got stuck with lodash and am getting an error. Any help would be much appreciated. The key nested will always be an array of 1 object.

const _ = require('lodash');

var all_data = [{id: 'A', nested: [{id: '123'}]}, {id: 'B', nested: [{id: '456'}]}];

_.map(all_data, (data) => ({
  data.nested_id = data.nested[0].id;

}));
console.log(all_data)

Desired output: [{id: 'A', nested_id: '123', nested: [{id: '123'}]}, {id: 'B', nested_id: '456', nested: [{id: '456'}]}]

Is there a reason why you are using lodash? The immediate problem is that you should return data from the callback of _.map but this can be done in pure JS and without mutation: all_data.map((obj) => ({ ...obj, nested_id: obj.nested[0].id })) — Andrew Li
– Andrew Li, Commented Feb 3, 2021 at 1:04

Arun Kumar Mohan · Accepted Answer · 2021-02-03 01:58:11Z

1

You don't have to use lodash for this simple transformation.

const allData = [{id: 'A', nested: [{id: '123'}]}, {id: 'B', nested: [{id: '456'}]}]

const transformedData = allData.map(item => ({
  ...item,
  nested_id: item.nested[0].id
}))

But here's the lodash version if you really want to use it.

const transformedData = _.map(allData, (item) => ({
  ...item,
  nested_id: item.nested[0].id,
}))

edited Feb 3, 2021 at 1:58

answered Feb 3, 2021 at 1:10

Arun Kumar Mohan

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3 Comments

user2242044 Over a year ago

Thanks. This works great. As a slight variant if I wanted to removed the property nested is it possible to do with the way that spread operator is used?

Arun Kumar Mohan Over a year ago

@user2242044 If you know the object only has the 3 properties shared in the code snippet, you can do allData.map(item => ({ id: item.id, nested_id: item.nested[0].id }))

user2242044 Over a year ago

thanks. This was just a simple example. What if it has a lot more fields than just 3 and I don't want to write them all out?

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