What would be an efficient algo in JavaScript to merge date time series?

June 25, 2023

I have the following time series list as input:

const ts1 = [
  ['2023-01-20', 1],
  ['2023-01-21', 2],
  ['2023-01-22', 3],
  ['2023-01-23', 4],
];

const ts2 = [
  ['2023-01-18', 5],
  ['2023-01-19', 6],
  ['2023-01-20', 7],
  ['2023-01-21', 8]
];

const ts3 = [
  ['2023-01-21', 9],
  ['2023-01-22', 10],
  ['2023-01-23', 11],
  ['2023-01-24', 12]
];

I’d like the output to be the merged (column stacked) version like so:

const output = [
  ['2023-01-18', null,    5, null],
  ['2023-01-19', null,    6, null],
  ['2023-01-20',    1,    7, null],
  ['2023-01-21',    2,    8,    9],
  ['2023-01-22',    3, null,   10],
  ['2023-01-23',    4, null,   11],
  ['2023-01-24', null, null,   12]
];

To give a bit more context, I’m reusing a REST API which provides the individual time-series and I need to compile the AnyChart required tableData format.

>Solution :

I’d go with something like

const merged = {};

let tses = [ts1, ts2, ts3];
for (let i = 0; i < tses.length; i++) {
  for (const [t, v] of tses[i]) {
    if (!merged[t]) merged[t] = new Array(tses.length).fill(null);
    merged[t][i] = v;
  }
}

console.log(Object.entries(merged).map(([t, vs]) => [t, ...vs]));

This outputs

[
  [ '2023-01-20', 1, 7, null ],
  [ '2023-01-21', 2, 8, 9 ],
  [ '2023-01-22', 3, null, 10 ],
  [ '2023-01-23', 4, null, 11 ],
  [ '2023-01-18', null, 5, null ],
  [ '2023-01-19', null, 6, null ],
  [ '2023-01-24', null, null, 12 ]
]

as expected.

For sorted order (since the keys are lexicographically sortable), do

console.log(Object.keys(merged).sort().map(key => [key, ...merged[key]]));

instead:

[
  [ '2023-01-18', null, 5, null ],
  [ '2023-01-19', null, 6, null ],
  [ '2023-01-20', 1, 7, null ],   
  [ '2023-01-21', 2, 8, 9 ],      
  [ '2023-01-22', 3, null, 10 ],  
  [ '2023-01-23', 4, null, 11 ],
  [ '2023-01-24', null, null, 12 ]
]