Javascript filter an array of objects by a property of object

Question

I have an array of userList which include user basic information.

this.state = {
    userList: [
        { name:"Ann", number:123456789 },
        { name:"Cathy", number:123456789 },
        { name:"Peter", number:123456789 },
        { name:"Ben", number:123456789 },
    ],
    vips: [ 
        { username:"Ann", years:2018 },
        { username:"Peter", years:2019 },
};

How I can return of the vips from userList? vips.username equals to userList.name

vips_return: [
        { name:"Ann", number:123456789 },
        { name:"Peter", number:123456789 },
]

I tried using .filter and .includes but I am not sure how to deal with objects.

const vips_return = userList.filter((user)=>
    vips.includes(user.name)
)

quirimmo · Accepted Answer · 2019-01-02 20:37:57Z

You can use a reduce and get the users in userList which are also in vips

const input = {
    userList: [
        { name:"Ann", number:123456789 },
        { name:"Cathy", number:123456789 },
        { name:"Peter", number:123456789 },
        { name:"Ben", number:123456789 },
    ],
    vips: [ 
        { username:"Ann", years:2018 },
        { username:"Peter", years:2019 },
    ]
};

console.log(input.userList.reduce((acc, val) => { 
  if(!!input.vips.find(vip => vip.username === val.name)) { 
    acc.push(val);
  } 
  return acc; 
}, []));

Considering that the length of vips should be lower than the one of userList, or at max the same (vips should be a subset of userList), maybe a better approach is to map over the vips and get back the corresponding user, like below:

const input = {
    userList: [
        { name:"Ann", number:123456789 },
        { name:"Cathy", number:123456789 },
        { name:"Peter", number:123456789 },
        { name:"Ben", number:123456789 },
    ],
    vips: [ 
        { username:"Ann", years:2018 },
        { username:"Peter", years:2019 },
    ]
};

console.log(input.vips.map(vip => input.userList.find(user => user.name === vip.username)));

Felix Kling · Accepted Answer · 2019-01-02 20:57:54Z

2

You can use find or findIndex:

userList.filter(user => vips.find(vip => vip.username === user.name));

find returns undefined if the value cannot be found in the array, so those are filtered out.

If you do this a lot and/or have a large data set, you should build a set of names first:

const vipNames = new Set(vips.map(vip => vip.username));

userList.filter(user => vipNames.has(user.name));

edited Jan 2, 2019 at 20:57

answered Jan 2, 2019 at 20:23

Felix Kling

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3 Comments

quirimmo Over a year ago

I think your field in case of vip should be username

susu watari Over a year ago

how can I get the value of type? after .find

Felix Kling Over a year ago

@susuwatari: I don't understand the question.

Nina Scholz · Accepted Answer · 2019-01-02 20:27:26Z

You could take a Map and get the wanted objects.

var state = { userList: [{ name: "Ann", number: 123456789 }, { name: "Cathy", number: 123456789 }, { name: "Peter", number: 123456789 }, { name: "Ben", number: 123456789 }], vips: [{ username: "Ann", years: 2018 }, { username: "Peter", years: 2019 }] },
    user = new Map(state.userList.map(o => [o.name, o])),
    vips = state.vips.map(({ username }) => user.get(username));
    
console.log(vips);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Or take a shorter approach with a double mapping

var state = { userList: [{ name: "Ann", number: 123456789 }, { name: "Cathy", number: 123456789 }, { name: "Peter", number: 123456789 }, { name: "Ben", number: 123456789 }], vips: [{ username: "Ann", years: 2018 }, { username: "Peter", years: 2019 }] },
    vips = state.vips
        .map(({ username }) => username)
        .map(Map.prototype.get, new Map(state.userList.map(o => [o.name, o])));
    
console.log(vips);

.as-console-wrapper { max-height: 100% !important; top: 0; }

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