How to merge objects in an array of objects, based on a property in the objects

Question

I have an array of activities like

this.activities = [
{
id: 54,
event_type: 'CA',
user_id: 56,
user_name: 'Anand',
purpose: disregard,
timestamp: 14356787
},
{
id: 54,
event_type: 'NA',
user_id: 56,
user_name: 'Anand',
purpose: 'privacy',
timestamp: ''
},
{
id: 54,
event_type: 'FA',
user_id: 56,
user_name: 'Anand',
purpose: 'Call',
timestamp: ''
},
{
id: 54,
event_type: 'FA',
user_id: 56,
user_name: 'Anand',
purpose: 'Listen',
timestamp: ''
},
{
id: 54,
event_type: 'CA',
user_id: 56,
user_name: 'Anand',
purpose: 'Not allowed',
timestamp: 14356784
},
{
id: 54,
event_type: 'NA',
user_id: 56,
user_name: 'Anand',
purpose: 'data',
timestamp: 14356786
},
{
id: 54,
event_type: 'CA',
user_id: 56,
user_name: 'Anand',
purpose: 'voicemail',
timestamp: 14356785
},
{
id: 54,
event_type: 'CA',
user_id: 56,
user_name: 'Anand',
purpose: 'phone',
timestamp: 14356775
},
{
id: 54,
event_type: 'CA',
user_id: 56,
user_name: 'Anand',
purpose: 'email',
timestamp: 14356776
},
{
id: 54,
event_type: 'CA',
user_id: 56,
user_name: 'Anand',
purpose: 'letter',
timestamp: 14356777
}
]

I want to group/filter this array by the event_type 'CA' only, based on a 5ms timestamp difference for each activity. So if timestamp of the activity with event_type 'CA' falls within 5ms of each other, then club those activities and form a new activity with everything same except a new event_type for the clubbed activities called CA_combined. So this array should like this

this.activities = [
{
id: 54,
event_type: 'CA_combined',
user_id: 56,
user_name: 'Anand',
purposes: ['disregard', 'Not allowed', 'voicemail'],
timestamp: 14356787
},
{
id: 54,
event_type: 'CA_combined',
user_id: 56,
user_name: 'Anand',
purposes: ['letter','email','phone']
timestamp: 14356777
},
{
id: 54,
event_type: 'NA',
user_id: 56,
user_name: 'Anand',
purpose: 'privacy',
timestamp: ''
},
{
id: 54,
event_type: 'FA',
user_id: 56,
user_name: 'Anand',
purpose: 'Call',
timestamp: ''
},
{
id: 54,
event_type: 'FA',
user_id: 56,
user_name: 'Anand',
purpose: 'Listen',
timestamp: ''
},
{
id: 54,
event_type: 'NA',
user_id: 56,
user_name: 'Anand',
purpose: 'data',
timestamp: 14356786
}
]

How do I go about achieving something like this? My try as of now, filter all of them whose event_type is CA and sort the array based on the timestamp value

let consentActivities = this.activities.filter(c => {
        if (c.event_type === 'CA') {
          return true
        } else {
          return false
        }
      })
consentActivities.sort((a, b) => {
        return b.timestamp - a.timestamp
      })

This is where I dont know how to group activities within a 5ms and completely losing it

 if (consentActivities.length && consentActivities[0].timestamp - consentActivities[consentActivities.length - 1].timestamp <= 5) {
        consentActivities[0].purposes = []
        consentActivities.forEach((p) => {
          consentActivities[0].purposes.push(p.purpose)
        })
        // consentActivities.splice(1, consentActivities.length)
      }

Any inputs are highly appreciated

I added my attempt at this in the edit, thanks. Appreciate your input — arch nemesis
– arch nemesis, Commented Jul 29, 2019 at 21:23
When you merge two events, you have 2 timestamps. What's your logic of merging a third event with the combined event? — MaxG
– MaxG, Commented Jul 29, 2019 at 21:26
@MaxG If the timestamp is within 5ms for activities, combine those activities and assign the largest timestamp of the activities which are combined. Does that answer your question? — arch nemesis
– arch nemesis, Commented Jul 29, 2019 at 21:28
Lets say three events occured at 0ms, 5ms, 10ms. Should they all be grouped? — Jonas Wilms
– Jonas Wilms, Commented Jul 29, 2019 at 21:34

Jonas Wilms · Accepted Answer · 2019-07-29 21:29:19Z

1

You already made the right first steps: Filter out CAs, sort, then you can easily group by accessing the previous index:

  const entries = data
    .filter(it => it.event_type === "CA")
    .sort((a, b) => a.timestamp - b.timestamp);

 const grouped = [];

 for(const entry of entries) {
   const previous = grouped[grouped.length - 1];
   if(previous && Math.abs(entry.timestamp - previous.timestamp) < 5) {
      previous.purposes.push(entry.purpose);
   } else {
     grouped.push({ id: entry.id, /*...*/, purposes: [entry.purpose] });
   }
}

answered Jul 29, 2019 at 21:29

Jonas Wilms

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2 Comments

arch nemesis Over a year ago

Hi Jonas, The result im getting is not the desired output like how I mentioned in the question. Im getting an array of objects with purposes in each array of all “CA” activities. What I need is club all the activities within 5ms of each other into one. Which means im guessing I need to use splice at some point

arch nemesis Over a year ago

Settled on this O(n) solution

arch nemesis · Accepted Answer · 2019-08-20 02:31:17Z

Settled on this O(n) solution

 sortedCAarray.forEach((act, index) => {
        const currActivityTime = moment(act.timestamp).valueOf()
        console.log(currActivityTime)
        //  First element is already added, avoid duplicates
        if (index < 1) return
        // Grab the last key from the timestampMap
        const timestampKeys = Object.keys(timestampMap)
        const key = timestampKeys[timestampKeys.length - 1]
        // Add the activity and purpose to the respective arrays and set for that key if the key is within 5 units of the current activity timestamp
        if (Math.abs(key - currActivityTime) < 5) {
          let activities = timestampMap[key].activities
          let purposes = timestampMap[key].purposes
          activities.push(act)
          purposes.add(act.purpose)
          let timestamp = moment(activities[activities.length - 1].timestamp).valueOf()
          // Edge case to to include all activities in the same bucket if they were within 5 ms of any element within the bucket
          if (timestamp > key) {
            Object.defineProperty(timestampMap, timestamp,
              Object.getOwnPropertyDescriptor(timestampMap, key))
            delete timestampMap[key]
          }
        } else {
          // If not just create a new key with the current activity timestamp as the key
          timestampMap[currActivityTime] = { activities: [act], purposes: new Set([act.purpose]) }
        }
      })

Would appreciate any improvements to this! Thank you

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