Given an array of timeseries data ordered from oldest to newest, return the sum of the values between the start and end dates (inclusive).

If either startDate or endDate is undefined, the sum is calculated to the start or end of the series, respectively. If both are undefined, the sum is calculated for the entire series.

Series data is expected to be an array of objects of the following format:

{ timestamp: Date, value: Number }

The algorithm is weighted toward sums that favor the end of the series array (most recent values), as it iterates from end to start.

Usage

var dateSum = require('timeseries-sum');

var startDate = new Date("June 3, 2016 GMT-0000"),
    endDate = new Date("June 5, 2016 GMT-0000"),
    series = [
      {
        timestamp: new Date("June 1, 2016 GMT-0000"),
        value: 1
      },
      {
        timestamp: new Date("June 2, 2016 GMT-0000"),
        value: 2
      },
      {
        timestamp: new Date("June 3, 2016 GMT-0000"),
        value: 4
      },
      {
        timestamp: new Date("June 4, 2016 GMT-0000"),
        value: 8
      },
      {
        timestamp: new Date("June 5, 2016 GMT-0000"),
        value: 16
      },
      {
        timestamp: new Date("June 6, 2016 GMT-0000"),
        value: 32
      },
    ];

// Calculate sum over a half-closed interval
dateSum(startDate, endDate, series);

// Calculate sum from the start of the interval to the end date
dateSum(undefined, endDate, series);

// Calculate sum from the start date to the end of the interval
dateSum(startDate, undefined, series);

// Calculate sum of the entire series
dateSum(undefined, undefined, series);