Dygraph: Date expected error! when using Array as data source in Angular 7 project

Question

Api project in ASP

[Route("api/[controller]")]
    public class SampleDataController : Controller
    {
        ...

        [HttpGet("[action]")]
        public Array GetGraphData()
        {
            var tsData = timeFloatService_.GetLatestDataRecords(4790, DataRecordStatus.Live, DataRecordAbnormal.Normal, 1).Get();
            object[][] result = tsData.Select(x => new object[] { x.Index.ToString("yyyy/MM/dd HH:mm:ss"), x.Value }).Take(10).ToArray();
            return result;
        }

Which is received in the calling Angular Project:

import { Component, OnInit, Inject } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-test',
  templateUrl: './test.component.html',
  styleUrls: ['./test.component.css']
})
export class TestComponent implements OnInit {

  private forecasts: any;

  constructor(http: HttpClient, @Inject('BASE_URL') baseUrl: string) {
    http.get<any[]>(baseUrl + 'api/SampleData/GetGraphData').subscribe(result => {
      this.forecasts = result;
    }, error => console.error(error));
  }

<p>
  test works!
</p>
<pre>{{forecasts|json}}</pre>
<ng-dygraphs [data]="forecasts"
             [options]=VALID OPTIONS NOT SHOWN FOR BREVITY
</ng-dygraphs>

Array of data is received, but the Date is a string not a Date() so the Dygraph chart isnt loaded!

Dygraphs is set up correctly(tested with csv data).

Even if I pass the Date as a DateTime it will be converted to a string! So my question is, how do I cast the first element of each array into a Date() inside an Angular project. I cant find any help on this at all!

See docs: http://dygraphs.com/data.html#array

CONSTRUCTOR AFTER CHANGES:

constructor(http: HttpClient, @Inject('BASE_URL') baseUrl: string) {
      http.get<any[]>(baseUrl + 'api/SampleData/GetGraphData').subscribe(result => {
        this.forecasts = from(result).pipe(map(item => [new Date(item[0]), item[1]]));
      }, error => console.error(error));

Above changes array to the following

{
  "_isScalar": false,
  "source": {
    "_isScalar": false,
    "array": [
      [
        "2013/01/01 00:00:00",
        58096
      ],
      [
        "2013/01/02 00:00:00",
        50893
      ],

Which unfortunately wont work! (Unless I've made an error.)

Need to change string to Date in DOM/Html page as the altered array was still displaying the date as a string!

Answer 1

You need to create date objects from the strings. You can do this using rxjs map.

Example:

import { from } from 'rxjs';
import { map } from 'rxjs/operators';
// ...
// observable array
const dates = from([
  "2013/01/01 00:00:00",
  "2013/01/02 00:00:00"
]);

dates.pipe(map(ds => new Date(ds))).subscribe(date => console.log(date));

In your case you'd obviously not map to a single date object but an array consisting of a date object and a value.

EDIT:

Ok, here's a more complete example for your case: https://stackblitz.com/edit/angular-jfx4gr

import { of } from 'rxjs';
import { map } from 'rxjs/operators';
// ...
httpGet = of([
    [
      "2013/01/01 00:00:00",
      58096
    ], [
      "2013/01/02 00:00:00",
      50893
    ]
]);

constructor() {
  this.httpGet
    .pipe(map(item => item.map(i => [ new Date(i[0]), i[1] ])))
    .subscribe(result => console.log(result));
}

Or actually you could make things even simpler by using array.map in your subscribe callback:

this.httpGet
    .subscribe(result => {
      const converted = result.map(i => [ new Date(i[0]), i[1] ]);
      console.log(converted);
    });