Html Heat Map Based On Value

Question

i have a table which is created dynamically from database.

            for (int m = 0; m < table.size(); m++) {

                out.print("<tr>");

                for (int k = 0; k < table.get(0).length; k++)

                {    out.print("<td width='10'>");
                     out.print(table.get(m)[k]);
                     out.println("</td>");
                }
                out.println("</tr>");

            }

I want to make a each cell coloured based on its value , The out put of my table is ;

Answer 1

Use HSL instead of RGB to represent your colors.

You will need something like this:

let table = '<table>';

for (let i = 0; i < 4; ++i) {

  table += '<tr>';

  for(let k = 0; k < 10; ++k) {
    const value = Math.random();
    const h = 240 - value * 240;
    
    table += '<td style="background: hsl(' + h + ', 100%, 50%)">' + value.toFixed(2) + '</td>';
  }

  table += '</tr>';
}

document.write(table);

table {
  border: 1px solid #000;
  border-collapse: collapse;
  font-family: Sans-Serif;
  color: #000;
}

td {
  border: 2px solid #000;
  padding: .5rem;
}

Ideally, add the style attributes in your backend so that the page that you send to the client already has the colors. If for any reason you can't do that, then just go over the cells in the client, reading their values and adding them the appropriated background color.

Using the other components of HSL you could generate different colors schemas. For example, a single-hue scale, with black and white on its ends and a colors of your choice in the middle, blue in this case:

let table = '<table>';

for (let i = 0; i < 4; ++i) {

  table += '<tr>';

  for(let k = 0; k < 10; ++k) {
    const value = Math.random();
    const l = value * 100;
    const textColor = l < 35 ? '#FFF' : '#000';
    
    table += '<td style="background: hsl(200, 100%, ' + l + '%); color: ' + textColor + '">' + value.toFixed(2) + '</td>';
  }

  table += '</tr>';
}

document.write(table);

table {
  border: 1px solid #000;
  border-collapse: collapse;
  font-family: Sans-Serif;
  color: #000;
}

td {
  border: 2px solid #000;
  padding: .5rem;
}