NODE.JS: iterating over an array of objects, creating a new key if it does not exist

Question

I am iterating over a collection of data, in my case, an array of objects. Here is a sample of 2 data points from it:

 {
violation_id: '211315',
inspection_id: '268804',
violation_category: 'Garbage and Refuse',
violation_date: '2012-03-22 0:00',
violation_date_closed: '',
violation_type: 'Refuse Accumulation' },

{
violation_id: '214351',
inspection_id: '273183',
violation_category: 'Building Conditions',
violation_date: '2012-05-01 0:00',
violation_date_closed: '2012-04-17 0:00',
violation_type: 'Mold or Mildew' }

I need to create a new array of objects from this, one for each "violation_category" property. If Violation category already exists in the new array I am creating, i simply add the information to that existing category object (instead of having two "building conditions" objects for example, I would just add to an existing one).

However, I am having trouble assigning to the existing object if the current one exists (it's easy to check if it does not, but not the other way around). This is what am attempting to do currently:

    if (violationCategory.uniqueCategoryName) {
  violationCategory.uniqueCategoryName.violations = results[i].violation_id;
  violationCategory.uniqueCategoryName.date = results[i].violation_date;
  violationCategory.uniqueCategoryName.closed =
    results[i].violation_date_closed;
} else {
  category.violations = results[i].violation_id;
  category.date = results[i].violation_date;
  category.closed = results[i].violation_date_closed;
  violationCategory.push(category);
}

In first condition, if this category (key) exists, I simply add to it, and in the second condition, this is where I am struggling. Any help appreciated. Thanks guys.

do you maybe want group by violation_category?

Aritra Chakraborty
– Aritra Chakraborty

2019-08-12 09:49:03 +00:00
Commented Aug 12, 2019 at 9:49 — Aritra Chakraborty
– Aritra Chakraborty, Commented Aug 12, 2019 at 9:49

Elad · Accepted Answer · 2019-08-12 09:54:20Z

1

Just add an empty object to the key if there no object there :

violationCategory.uniqueCategoryName = violationCategory.uniqueCategoryName || {};

And only then, add the data you want to the object.

   violationCategory.uniqueCategoryName.violations = results[i].violation_id;
   violationCategory.uniqueCategoryName.date = results[i].violation_date;
   violationCategory.uniqueCategoryName.closed =
   results[i].violation_date_closed;

No condition needed.

Good luck!

edited Aug 12, 2019 at 9:54

answered Aug 12, 2019 at 9:46

Elad

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3 Comments

TomK Over a year ago

Thanks buddy, if I wanted the "category name" to exist as a key in the object, itself holding an object with the date, id, and closed value...do you have any idea how I could do that?

Elad Over a year ago

@TomK I Don't sure what are you asking about. you want uniqueCategoryName to be an variable? if so you can access the object with a variable like so: violationCategory[uniqueCategoryName].whatEverSubKeyYouWant = 'value';

TomK Over a year ago

it's ok I figured it out =)

Lajos Arpad · Accepted Answer · 2019-08-12 09:55:40Z

1

Assuming that you have an input variable which is an array of objects, where the objects are looking like the objects of the question, you can generate your output like this:

var output = {};
for (var item of input) {
    if (!output[item.violation_category]) output[item.violation_category] = [];
    output[item.violation_category].push(item);
}

Of course you might customize it like you want.

answered Aug 12, 2019 at 9:55

Lajos Arpad

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