I would like to know how to reduce a large array of objects based upon several properties. The array looks like:
[{count:4, district:19, to_timestamp:"2015-09-24T00:00:00.000Z", type:"MOTOR VEHICLE THEFT"},
{count:6, district:12, to_timestamp:"2015-09-24T00:00:00.000Z", type:"MOTOR VEHICLE THEFT"},
{count:14, district:19, to_timestamp:"2015-10-01T00:00:00.000Z", type:"MOTOR VEHICLE THEFT"},
{count:4, district:19, to_timestamp:"2015-09-24T00:00:00.000Z", type:"VANDALISM"},
...
{count:4, district:19, to_timestamp:"2016-03-24T00:00:00.000Z", type:"MOTOR VEHICLE THEFT"},
{count:7, district:10, to_timestamp:"2016-03-24T00:00:00.000Z", type:"ASSAULT"}]
Resulting reduced array of objects needs to include the aggregate count
from every district
for given crime type
on any given date ( to_timestamp
); dates are weekly. Something like:
[{key: "MOTOR VEHICLE THEFT", value: 57, date:"2015/09/23"},
...
{key: "ASSAULT", value: 77, date:"2016/03/23"}]
I'm already using Moment for date conversions.
You could use an object as hash table for the wanted groups ( type
and to_timestamp
) and use Array#forEach
for iterating the array.
var data = [{ count: 4, district: 19, to_timestamp: "2015-09-24T00:00:00.000Z", type: "MOTOR VEHICLE THEFT" }, { count: 6, district: 12, to_timestamp: "2015-09-24T00:00:00.000Z", type: "MOTOR VEHICLE THEFT" }, { count: 14, district: 19, to_timestamp: "2015-10-01T00:00:00.000Z", type: "MOTOR VEHICLE THEFT" }, { count: 4, district: 19, to_timestamp: "2015-09-24T00:00:00.000Z", type: "VANDALISM" }, { count: 4, district: 19, to_timestamp: "2016-03-24T00:00:00.000Z", type: "MOTOR VEHICLE THEFT" }, { count: 7, district: 10, to_timestamp: "2016-03-24T00:00:00.000Z", type: "ASSAULT" }], groupBy = ['type', 'to_timestamp'], grouped = []; data.forEach(function (a) { var key = groupBy.map(function (k) { return a[k]; }).join('|'); if (!this[key]) { this[key] = { key: a.type, value: 0, date: a.to_timestamp.slice(0, 10).replace(/-/g, '/') }; grouped.push(this[key]); } this[key].value += a.count; }, Object.create(null)); console.log(grouped);
but I think you reduce a object will be easier more then a array. after you got a object, you can convert it to a array
This code are just combine the data
and type
to the object key. Did not add district
.
const object = [{count:4, district:19, to_timestamp:"2015-09-24T00:00:00.000Z", type:"MOTOR VEHICLE THEFT"}, {count:6, district:12, to_timestamp:"2015-09-24T00:00:00.000Z", type:"MOTOR VEHICLE THEFT"}, {count:14, district:19, to_timestamp:"2015-10-01T00:00:00.000Z", type:"MOTOR VEHICLE THEFT"}, {count:4, district:19, to_timestamp:"2015-09-24T00:00:00.000Z", type:"VANDALISM"}, {count:4, district:19, to_timestamp:"2016-03-24T00:00:00.000Z", type:"MOTOR VEHICLE THEFT"}, {count:7, district:10, to_timestamp:"2016-03-24T00:00:00.000Z", type:"ASSAULT"}] // reduce a object .reduce( ( res, item) => { const date = moment(item.to_timestamp).format('YYYY/MM/DD') const key = item.type + date if ( !res[key] ) { res[key] = {key: item.type, date: date, value: item.count} } else { res[key]['value'] += item.count } return res }, {} ) //get a object, and then the object to array //console.log(object) var result = [] for ( var key in object ) { result.push(object[key]) } console.log(result)
<script src="http://momentjs.com/downloads/moment.min.js"></script>
I think you can do this with a simple Array.prototype.forEach
loop:
var crimes = [ {count:4, district:19, to_timestamp:"2015-09-24T00:00:00.000Z", type:"MOTOR VEHICLE THEFT"}, {count:6, district:12, to_timestamp:"2015-09-24T00:00:00.000Z", type:"MOTOR VEHICLE THEFT"}, {count:14, district:19, to_timestamp:"2015-10-01T00:00:00.000Z", type:"MOTOR VEHICLE THEFT"}, {count:4, district:19, to_timestamp:"2015-09-24T00:00:00.000Z", type:"VANDALISM"}, {count:4, district:19, to_timestamp:"2016-03-24T00:00:00.000Z", type:"MOTOR VEHICLE THEFT"}, {count:7, district:10, to_timestamp:"2016-03-24T00:00:00.000Z", type:"ASSAULT"} ]; var dict = {}, result = []; crimes.forEach(crime => { var date = new Date(crime.to_timestamp); date.setDate(date.getDate() - date.getDay()); var hash = crime.type + date.toDateString() if (!dict[hash]) { dict[hash] = { count: crime.count, key: crime.type, date: date }; result.push(dict[hash]) } else dict[hash].count += crime.count; }); console.log(result);
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