Group and sum range of hours by the hour

group-by-hours.js

var _ = require('lodash');

var ranges = [
  ["12:00", 0.0], ["12:15", 0.0], ["12:30", 0.0], ["12:45", 0.0],
  ["01:00", 0.0], ["01:15", 0.0], ["01:30", 0.0], ["01:45", 0.0],
  ["02:00", 0.0], ["02:15", 0.0], ["02:30", 0.0], ["02:45", 0.0],
  ["03:00", 0.0], ["03:15", 0.0], ["03:30", 0.0], ["03:45", 0.0],
  ["04:00", 0.0], ["04:15", 0.0], ["04:30", 0.0], ["04:45", 0.0],
  ["05:00", 0.0], ["05:15", 0.0], ["05:30", 0.0], ["05:45", 0.0],
  ["06:00", 0.0], ["06:15", 0.0], ["06:30", 0.0], ["06:45", 0.0],
  ["07:00", 10.0], ["07:15", 328.0], ["07:30", 1249.0], ["07:45", 2554.0],
  ["08:00", 3947.0], ["08:15", 5263.0], ["08:30", 6431.0], ["08:45", 6861.0],
  ["09:00", 6904.0], ["09:15", 7006.0], ["09:30", 7046.0], ["09:45", 6909.0]
];

var result = {};

_.forEach(ranges, function (n, index) {
  // Get the whole hour from the hour log.
  var key = n[0].split(':')[0];
  
  // The number of hours for the given log.
  var val = n[1];
  
  // Set or incriment the hour total.
  result[key] ? 
    result[key] += val :
    result[key] = val;
});

/*
Result:

{ '12': 0,
  '01': 0,
  '02': 0,
  '03': 0,
  '04': 0,
  '05': 0,
  '06': 0,
  '07': 4141,
  '08': 22502,
  '09': 27865 }
  
*/

// Turn the result into an array of arrays.
var result = _.zip(_.keys(result), _.values(result));

console.log(result);

/*
Result:

[ [ '12', 0 ],
  [ '01', 0 ],
  [ '02', 0 ],
  [ '03', 0 ],
  [ '04', 0 ],
  [ '05', 0 ],
  [ '06', 0 ],
  [ '07', 4141 ],
  [ '08', 22502 ],
  [ '09', 27865 ] ]
*/