Javascript: How to get a unique list of values assigned to the same property from an array of objects?

Question

I'm trying to make a unique list of all the values assigned to the city property, which is buried in an object within an object, and I have an array of such objects

buildings = [ { name: 'Victoria Bell Tower', filterOptions: { city: 'Ottowa', state: 'Canada', buildingType: 'Parliament Building', }, }, { name: 'Cathedral', filterOptions: { city: 'Washington D.C.', state: '', buildingType: 'Cathedral', }, }, { name: 'Post Office', filterOptions: { city: 'Washington D.C.', state: '', buildingType: 'Post Office', }, }]

What's a practical way to get a unique array of the cities properties:

cities = ['Ottowa', 'Washington D.C.']

Ryan Nghiem · Accepted Answer · 2020-01-31 04:15:47Z

2

You can try my simple code:

let arr = buildings.map(b => {
  return b.filterOptions.city
})
console.log([...new Set(arr)]);

answered Jan 31, 2020 at 4:15

Ryan Nghiem

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4 Comments

Mugunga Over a year ago

This doesn't remove dups, though right? I need uniqe values for a dropdown

Ryan Nghiem Over a year ago

Do you try? This is a demo: codepen.io/phuongnm153/pen/oNgreZy

customcommander Over a year ago

@Mugunga It would because of the use of Set which filters out duplicates

Mugunga Over a year ago

Ah, yes that works, thank you. Why does it need the [... ] around the new set instead of just: log(new Set(arr));

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