How can I create a time series line graph in chart.js?

Question

I created a python script that fetches data from an API to get weather temperature at a certain time

The result is a CSV file that looks like this:

Time,Temperature
2020-02-15 18:37:39,-8.25
2020-02-15 19:07:39,-8.08
2020-02-15 19:37:39,-8.41
2020-02-15 20:07:39,-8.2

How can transform the CSV into a JavaScript array and make a Chart.js line chart out of it?

Right now, I have a Chart.js base script that looks like this (isn't filled with any data)

new Chart(document.getElementById("line-chart"), {
type: 'line',
 data: {
   labels: [],
   datasets: [{ 
       data: [],
       label: "Temperature",
       borderColor: "#3e95cd",
       fill: false
     } 
   ]
 },
 options: {
   scales: {
     xAxes: [{
       type: 'time',
       distribution: 'linear',
     }],
   title: {
     display: false,
   }
   }
 }
});

Answer 1

Basically, convert every single file-line string:

2020-02-15 18:37:39,-8.25 

into an Object:

{x: "2020-02-15 18:37:39", y: -8.25}

to be stored inside the Chart.js data : [] Array.

Here's an example on how to create a function csvToChartData() that returns such an Array (to be used like: ... data: csvToChartData(csv) )

• Trim and split a file string by newline \n into a lines array .
• Remove titles (the first array key) by using lines.shift();
• Convert every line to an object {x: date, y: temperature} by splitting each line by comma .split(',')
• Pass that newly mapped Array (by using .map()) as your chart data:

const csv = `Time,Temperature
2020-02-15 18:37:39,-8.25
2020-02-15 19:07:39,-8.08
2020-02-15 19:37:39,-8.41
2020-02-15 20:07:39,-8.2`;

const csvToChartData = csv => {
  const lines = csv.trim().split('\n');
  lines.shift(); // remove titles (first line)
  return lines.map(line => {
    const [date, temperature] = line.split(',');
    return {
      x: date,
      y: temperature
    }
  });
};

const ctx = document.querySelector("#line-chart").getContext('2d');
const config = {
  type: 'line',
  data: {
    labels: [],
    datasets: [{
      data: csvToChartData(csv),
      label: "Temperature",
      borderColor: "#3e95cd",
      fill: false
    }]
  },
  options: {
    scales: {
      xAxes: [{
        type: 'time',
        distribution: 'linear',
      }],
      title: {
        display: false,
      }
    }
  }
};
new Chart(ctx, config);

#line-chart {
  display: block;
  width: 100%;
}

<canvas id="line-chart"></canvas>
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.24.0/moment.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/[email protected]"></script>

Fetch data dynamically:

To fetch the data dynamically, say every 5 seconds, you could use AJAX and the Fetch API.
Here's the modified JS example given you have a CSV file called temperature.csv

const config = {
  type: "line",
  data: {
    labels: [],
    datasets: [{
      data: [], // Set initially to empty data
      label: "Temperature",
      borderColor: "#3e95cd",
      fill: false
    }]
  },
  options: {
    scales: {
      xAxes: [{
        type: "time",
        distribution: "linear"
      }],
      title: {
        display: false
      }
    }
  }
};

const ctx = document.querySelector("#line-chart").getContext("2d");
const temperatureChart = new Chart(ctx, config);

const csvToChartData = csv => {
  const lines = csv.trim().split("\n");
  lines.shift(); // remove titles (first line)
  return lines.map(line => {
    const [date, temperature] = line.split(",");
    return {
      x: date,
      y: temperature
    };
  });
};

const fetchCSV = () => fetch("temperature.csv")
  .then(data => data.text())
  .then(csv => {
    temperatureChart.data.datasets[0].data = csvToChartData(csv);
    temperatureChart.update();
    setTimeout(fetchCSV, 5000); // Repeat every 5 sec
  });

fetchCSV(); // First fetch!