Google Sheets – How to Colorize a Cell Based on Cell Data

conditional formattinggoogle sheetsgoogle-apps-script

I'd like to colorize a cell based on its contents. 0 = red, 100 = green, and linearly interpolated between.

function LinInt(x){    
  var ss = SpreadsheetApp.getActiveSheet();
  var cell = ss.getActiveRange();
  var hue;
  hue = (x/100)*120;

  var color = HSVtoRGB(hue, 40, 100);
  cell.setBackground(color);

  return x;    
}   

function HSVtoRGB(h, s, v) {
    var r, g, b, i, f, p, q, t;
    if (h && s === undefined && v === undefined) {
        s = h.s, v = h.v, h = h.h;
    }
    i = Math.floor(h * 6);
    f = h * 6 - i;
    p = v * (1 - s);
    q = v * (1 - f * s);
    t = v * (1 - (1 - f) * s);
    switch (i % 6) {
        case 0: r = v, g = t, b = p; break;
        case 1: r = q, g = v, b = p; break;
        case 2: r = p, g = v, b = t; break;
        case 3: r = p, g = q, b = v; break;
        case 4: r = t, g = p, b = v; break;
        case 5: r = v, g = p, b = q; break;
    }
  return '#'+((b | g << 8 | r << 16) / 0x1000000).toString(16).substring(2);
}

When I do this I get an error saying that I am not allowed to call setBackground. I assume this is because I'm not allowed to change the color of one cell from another because I'm screwing up getting the current cell that the function is running in.

How do I get the cell that the function is running in so that I can call setBackground() on it?

For example, I'd like to type =LinInt(50) into cell A1 and have A1 be yellow and have the number 50 in it. Then when I type =LinInt(100) into cell A2 it is green and has the number 100 in it.

Best Answer

I've just had a go at this, and here's a more flexible function. The previous example couldn't properly handle ranges of selected cells, this one can (but you could also add some better error checking for empty ranges!) Could easily be customized to have other ranges of brightness, hues, auto-calculation of max value, etc.:

/**
 * Adds a custom menu to the active spreadsheet, containing a single menu item
 * for invoking the readRows() function specified above.
 * The onOpen() function, when defined, is automatically invoked whenever the
 * spreadsheet is opened.
 * For more information on using the Spreadsheet API, see
 * https://developers.google.com/apps-script/service_spreadsheet
 */

function onOpen() {
  var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();

  var menu = [({name: "colorize", functionName: "colorize"})];
  spreadsheet.addMenu("HSV Colors", menu);
}

/*
 * Change saturation of cell background colors based on their values
 */

function colorize() {

  // Prompt the user for a max value number.
  var numberRange = Browser.inputBox('Colorize Range',
      'Please enter the maximum number of your range' +
      ' (for example, "2"):',
      Browser.Buttons.OK_CANCEL);
  if (numberRange == 'cancel') {
    return;
  }

  // Prompt the user for a hue number.
  var hue = Browser.inputBox('Colorize Range',
      'Please enter the hue (0-359)' +
      ' (for example, "128"):',
      Browser.Buttons.OK_CANCEL);
  if (hue == 'cancel') {
    return;
  }


  var range = SpreadsheetApp.getActiveRange();
  Logger.log('range:' + range);

  var values = range.getValues(); // [][]

  Logger.log('values:' + values);

  var backgrounds = [];

  for (var row = 0; row < range.getNumRows(); row++) 
  {
    var rowBackgrounds = [];
    for (var column = 0; column < range.getNumColumns(); column++) 
    {
      var val = Number(values[row][column]);
      if (isNaN(val)) 
      {
        val = 0;
      }
      var newColor = HSVtoHEX(hue,255*val/numberRange,200);
      rowBackgrounds.push(newColor);
    }
    backgrounds.push(rowBackgrounds);
  }
  range.setBackgrounds(backgrounds);
}


// http://stackoverflow.com/a/17243070/1536038
function HSVtoHEX(h, s, v) {

  Logger.log('h:'+h+' s:'+s + ' v:' + v);

    var r, g, b, i, f, p, q, t;

    // turn variables into degrees and percentages
    h=h/360, s=s/255, v=v/255;

    if (h && s === undefined && v === undefined) {
        s = h.s, v = h.v, h = h.h;
    }
    i = Math.floor(h * 6);
    f = h * 6 - i;
    p = v * (1 - s);
    q = v * (1 - f * s);
    t = v * (1 - (1 - f) * s);
    switch (i % 6) {
        case 0: r = v, g = t, b = p; break;
        case 1: r = q, g = v, b = p; break;
        case 2: r = p, g = v, b = t; break;
        case 3: r = p, g = q, b = v; break;
        case 4: r = t, g = p, b = v; break;
        case 5: r = v, g = p, b = q; break;
    }

    //http://stackoverflow.com/a/5624139/1536038
  var result = "#" + ((1 << 24) + (Math.floor(r * 255) << 16) + 
      (Math.floor(g * 255) << 8) + Math.floor(b * 255))
      .toString(16).slice(1);
  Logger.log(result);
    return result;
}
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