Is there a way to loop over array of arrays of objects?

Question

This is how my solution should look like:

Right now I have an array where I group them all by there first letter like so

const grouped = _.groupBy(topicPages, key => key.relatedTopic.title[0]);

And this is the result :

So I am trying to figure out a way to display the Letter A with the titles that are in that array.

I have tried using some sort of map :

grouped.map(first, key) => {
  // here I want to display the key

 // and then continue looping over 
  first.map(title => {
    title.relatedTopic.title
  })
})

_.forEach() over it, since you're using Lodash. Or use any of the other Lodash methods that work here like _.entries() or something. Or loop over Object.entries() without Lodash. How you display those results seems like a separate issue, though. — VLAZ
– VLAZ, Commented Apr 15, 2021 at 9:23
Thanks, I will update my question to try and describe my problem better! — Eirik Vattøy
– Eirik Vattøy, Commented Apr 15, 2021 at 9:34

Jamiec · Accepted Answer · 2021-04-15 09:58:57Z

2

I get : TypeError: grouped.map is not a function

grouped is an object, which does not have a map function.

const input = ["All","Andre","Ben","Boy"];

const grouped = _.groupBy(input, item => item[0]);

console.log(grouped)

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.21/lodash.min.js"></script>

In order to loop over it you probably want the entries

const input = ["All","Andre","Ben","Boy"];

const grouped = _.groupBy(input, item => item[0]);

_.forEach(_.entries(grouped), ([key,values]) => {
    console.log(key);
    values.forEach(value => {
       console.log("\t" + value);
    })
})

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.21/lodash.min.js"></script>

edited Apr 15, 2021 at 9:58

answered Apr 15, 2021 at 9:35

Jamiec

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5 Comments

Jamiec Over a year ago

@PeterSeliger you could imply their structure from key.relatedTopic.title in the question, but this answer does not need to understand their structure - it describes the required implementation of iterating a grouped object

VLAZ Over a year ago

_.forEach already loops over keys and values of an object. But puts the key as second parameter. Your code is equivalent to _.forEach(grouped, (values, key) => /*no further changes needed*/ Demo

Jamiec Over a year ago

Thanks @VLAZ that's what I should have done

Eirik Vattøy Over a year ago

@Jamiec Can I ask why key and value is wrapped inside brackets? I can't figure out what is does

Jamiec Over a year ago

@EirikVattøy it destructures the array. _.entries returns an array like [key.value] and that just destructures it to variables key and values. More info here: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

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