Add matching values from one array to an array of original object

Question

I have a users list like the following:

[
    {
        user: a,
        email: a.com,
        events: []
    },
    {
        user: b,
        email: b.com
        events: []
    }       
]

And an events list:

[
    {
        user: a,
        start: 2020-01-01
        end: 2020-01-02
    },
    {
        user: a,
        start: 2020-02-01
        end: 2020-02-02
    },    
    {
        user: b,
        start: 2020-03-01
        end: 2020-03-02
    },     
]

And I'm trying to combine the list of events by user into a array on the original users object like so:

[
    {
        user: a,
        email: a.com,
        events: [
            {
                start: 2020-01-01
                end: 2020-01-02
            },
            {
                start: 2020-02-01
                end: 2020-02-02
            }
        ]
    },
    {
        user: b,
        email: b.com,
        events: [
            {
                start: 2020-03-01
                end: 2020-03-02
            }
        ]
    }       
]

My original intuition is to simply iterate over the events list by each user and where they match by user value, push a new object to the users.events array. However, I'm not a JS pro, and I'm sure there's a combination of assign/filter/map/reduce or lodash that streamlines this type of problem. Any help is greatly appreciated!

Everest Climber · Accepted Answer · 2020-10-18 00:32:07Z

1

Please try this:

const userEvents = [
    {
        user: a,
        email: a.com,
        events: []
    },
    {
        user: b,
        email: b.com,
        events: []
    }       
]

const userStartEnds = [
    {
        user: a,
        start: 2020-01-01,
        end: 2020-01-02
    },
    {
        user: a,
        start: 2020-02-01,
        end: 2020-02-02
    },    
    {
        user: b,
        start: 2020-03-01,
        end: 2020-03-02
    },     
]

[
    {
        user: a,
        email: a.com,
        events: [
            {
                start: 2020-01-01,
                end: 2020-01-02
            },
            {
                start: 2020-02-01,
                end: 2020-02-02
            }
        ]
    },
    {
        user: b,
        email: b.com,
        events: [
            {
                start: 2020-03-01,
                end: 2020-03-02
            }
        ]
    }       
]

userEvents.map((userEvent) => ({
  ...userEvent,
  events: userStartEnds
    .filter(({ user }) => (userEvent.email === user.email))
    .map(({ start, end }) => ({ start, end }))
}))

edited Oct 18, 2020 at 0:32

answered Oct 17, 2020 at 20:29

Everest Climber

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2 Comments

user1710344 Over a year ago

Works like a charm! In the filter, I used .filter(user => userEvent.email === user.email) ... any reason for the ({ })?

Everest Climber Over a year ago

Just edited filter, map implementation. Orignal one couldn't work properly as I didn't return JSON as ({ }). You can return JSON as ({ }) without function processing. This is kind of arrow function usage, and please check arrow function document if possible.

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