How to group a javascript object array by multiple of its properties?
I'd propose this transformation:
var showtimesData = [ {"location":"location1", "date":"31-12-2016", "time":"1:00"}, {"location":"location1", "date":"31-12-2016", "time":"2:00"}, {"location":"location1", "date":"01-01-2017", "time":"3:00"}, {"location":"location1", "date":"01-01-2017", "time":"4:00"}, {"location":"location2", "date":"31-12-2016", "time":"1:00"}, {"location":"location2", "date":"31-12-2016", "time":"2:00"}, {"location":"location2", "date":"01-01-2017", "time":"3:00"}, {"location":"location2", "date":"01-01-2017", "time":"4:00"}, ]; var transformed = showtimesData.reduce(function(obj, show){ //var { location, date, time } = show; //if destructuring is available var location = show.location, date = show.date, time = show.time, objLocation = obj[location] = obj[location] || { dates : { } }, dates = objLocation.dates, date = dates[date] = dates[date] || [ ]; date.push(time); return obj;}, {});results.innerHTML = JSON.stringify(transformed, null, '\t');<pre id="results"></pre>But if you really want to transform it to that, I'd propose grabing this transformation and map it to your proposed structure.
var showtimesData = [ {"location":"location1", "date":"31-12-2016", "time":"1:00"}, {"location":"location1", "date":"31-12-2016", "time":"2:00"}, {"location":"location1", "date":"01-01-2017", "time":"3:00"}, {"location":"location1", "date":"01-01-2017", "time":"4:00"}, {"location":"location2", "date":"31-12-2016", "time":"1:00"}, {"location":"location2", "date":"31-12-2016", "time":"2:00"}, {"location":"location2", "date":"01-01-2017", "time":"3:00"}, {"location":"location2", "date":"01-01-2017", "time":"4:00"}, ]; var transformed = showtimesData.reduce(function(obj, show){ //var { location, date, time } = show; //if destructuring is available var location = show.location, date = show.date, time = show.time, objLocation = obj[location] = obj[location] || { dates : { } }, dates = objLocation.dates, date = dates[date] = dates[date] || [ ]; date.push(time); return obj;}, {});var secondTransformed = Object.keys(transformed).map(function(key){ var dates = transformed[key].dates, transformedDates = Object.keys(dates).map(function(key){ return { date : key, times : dates[key] } }); return { location : key, dates : transformedDates }});results.innerHTML = JSON.stringify(secondTransformed, null, '\t');<pre id="results"></pre>Although there are better ways to do this (performance wise).
This proposal features just Array.prototype.reduce() with one temporary object for referencing the array items.
var showtimesData = [{ "location": "location1", "date": "31-12-2016", "time": "1:00" }, { "location": "location1", "date": "31-12-2016", "time": "2:00" }, { "location": "location1", "date": "01-01-2017", "time": "3:00" }, { "location": "location1", "date": "01-01-2017", "time": "4:00" }, { "location": "location2", "date": "31-12-2016", "time": "1:00" }, { "location": "location2", "date": "31-12-2016", "time": "2:00" }, { "location": "location2", "date": "01-01-2017", "time": "3:00" }, { "location": "location2", "date": "01-01-2017", "time": "4:00" }, ], showtimesByLocationByDate = showtimesData.reduce(function (r, a) { var o; if (!(a.location in r.obj)) { o = { location: a.location, dates: [] }; r.obj[a.location] = { dates: o.dates }; r.array.push(o); } if (!(a.date in r.obj[a.location])) { o = { date: a.date, times: [] }; r.obj[a.location].dates.push(o); r.obj[a.location][a.date] = o.times; } r.obj[a.location][a.date].push(a.time); return r; }, { array: [], obj: {} }).array;document.write('<pre>' + JSON.stringify(showtimesByLocationByDate, 0, 4) + '</pre>');Bonus: Generic version with a given data structure
var showtimesData = [{ "location": "location1", "date": "31-12-2016", "time": "1:00" }, { "location": "location1", "date": "31-12-2016", "time": "2:00" }, { "location": "location1", "date": "01-01-2017", "time": "3:00" }, { "location": "location1", "date": "01-01-2017", "time": "4:00" }, { "location": "location2", "date": "31-12-2016", "time": "1:00" }, { "location": "location2", "date": "31-12-2016", "time": "2:00" }, { "location": "location2", "date": "01-01-2017", "time": "3:00" }, { "location": "location2", "date": "01-01-2017", "time": "4:00" }, ], structure = [ { key: 'location', data: 'dates' }, { key: 'date', data: 'times' }, { key: 'time' } ], showtimesByLocationByDate = showtimesData.reduce(function (r, a) { var properties = structure.slice(), lastKey = properties.pop().key; properties.reduce(function (rr, b) { var o = {}, p = {}, key = b.key, value = a[key], array = b.data; if (!(value in rr.obj)) { o[key] = value; o[array] = []; p[array] = o[array]; rr.obj[value] = p; rr.array.push(o); } return { array: rr.obj[value][array], obj: rr.obj[value] }; }, r).array.push(a[lastKey]); return r; }, { array: [], obj: {} }).array;document.write('<pre>' + JSON.stringify(showtimesByLocationByDate, 0, 4) + '</pre>');