Filter/Reduce array of objects into a new object based on day

Question

Consider the following array of objects:

const data = [
   *{...more data from previous dates}*,
   {
     unixDate: 1650348034,  //yesterday
     dateTime: Tue Apr 19 2022 23:00:34,
     severityLevel: 1,
     severity: "Light"
   },
   {
     unixDate: 1650348034,  //yesterday
     dateTime: Tue Apr 19 2022 14:00:34,
     severityLevel: 3,
     severity: "Moderate"
   },
   {
     unixDate: 1650440700,  //today
     dateTime: Wed Apr 20 2022 15:45:00,
     severityLevel: 2,
     severity: "Moderate-Light"
   },
   {
     unixDate: 1650442500,  //today
     dateTime: Wed Apr 20 2022 15:45:00,
     severityLevel: 4,
     severity: "Heavy"
   },
   {
     unixDate: 1650427234,  //today
     dateTime: Wed Apr 20 2022 12:00:00,
     severityLevel: 3,
     severity: "Moderate"
   }

]

I would like to return the following:

{
   *///...records from previous dates,* 
   1650348034 : 2, //yesterday record taking only one of the unixtimestamp, and the average value of 'severityLevel'.
   1650440700 : 3  //same as above but unixtimestamp is today.
}

I'm using the dayjs package to determine whether or not the date is today, via the isToday plugin, but couldn't think of how to compare the dates. The data is growing everyday as it records new readings. I'm not too familiar with the array filter/reduce methods in ES6, would they be useful here? Any help is appreciated!

Answer 1

Gets a unique list of days and builds an object based on the calculated days

const data = [ { unixDate: 1650348034, dateTime: "Tue Apr 19 2022 23:00:34", severityLevel: 1, severity: "Light" }, { unixDate: 1650348034, dateTime: "Tue Apr 19 2022 14:00:34", severityLevel: 3, severity: "Moderate" }, { unixDate: 1650440700, dateTime: "Wed Apr 20 2022 15:45:00", severityLevel: 2, severity: "Moderate-Light" }, { unixDate: 1650442500, dateTime: "Wed Apr 20 2022 15:45:00", severityLevel: 4, severity: "Heavy" }, { unixDate: 1650427234, dateTime: "Wed Apr 20 2022 12:00:00", severityLevel: 3, severity: "Moderate" } ]

//Get unique list of days
let unique = [... new Set(data.map(d => new Date(d.unixDate * 1000).toLocaleDateString("en-US")))];

//build object based on this list
let results = Object.fromEntries(unique.map(m => {
  let records = data.filter(v => new Date(v.unixDate * 1000).toLocaleDateString("en-US") === m); 
  return [records[0].unixDate, records.reduce((v,o) => v+=o.severityLevel, 0) / records.length ]
}));

console.log(results);