How do I visualize points in a FeatureCollection based on feature properties using Google Earth Engine?

Question

New user of Earth Engine and Javascript here. I have a FeatureCollection of points. These points are field observations where researchers have marked water sources, and noted whether or not they were dry at the time of observation. Basically, I would like to display these points in GEE with a different color for "dry" and "wet" observations. The water status is the "water_stat" property of each feature. I figure I should be able to assign a color for each status, but I haven't been able to work it out.

So far, I have tried FeatureCollection.draw(), but there doesn't seem to be an easy way to draw unique colors based on a feature property.

I have also tried Image.paint(), but I can't control the radius of the points that are displayed on the map: it only colors one pixel for each point. If I can get it to color more than one pixel, I think I can figure out how to get it to color those points uniquely - but I'm not going down that road if I can't figure out the one-pixel problem first.

So, I see two options: 1) figure out how to FeatureCollection.draw() with different colors, or 2) figure out how to control the radius of points, using Image.paint() - possibly by buffering the points somehow. Any ideas on how to work out either of these approaches? Code is linked and displayed below.

https://code.earthengine.google.com/8c9787c9a118b7661f62355f0715c9ef

    //This script adds field observations of water presence to the map.

   // Import features
   var fieldObs = ee.FeatureCollection("users/ansoncall/FieldObservations");

  // Adds the field observations to the map. 
  Map.addLayer(fieldObs.draw({color: 'ff0000', pointRadius: 5}), {}, 'Field 
  Observations'); //Can't add unique colors with .draw()??

  // Create an empty image into which to paint the features, cast to byte.
  var emptyObs = ee.Image().byte();

  // Paint all the polygon edges with the same number and width, display.
  var outlineObs = emptyObs.paint({
    featureCollection: fieldObs,
    color: 1, // Can enter a feature property if different colors are needed 
  for different features. Not done yet but I think I can figure out that 
  part
  });

  // Add custom color layer to map
  Map.addLayer(outlineObs, {palette: '#00ff00'}, 'Color-Coded 
  Observations'); //Only ONE pixel is colored!

  // Prints the field observations to the console
  print(fieldObs, 'Field Observations'); //

Answer 1

The Google Earth Engine Developers group just provided two solutions - one quick fix and one more elegant.

The quick fix - filter out the "wet" features, then add those as a unique layer. Then filter out the "dry" features, and add those as a second layer. Here's the code used to filter out wet features:

    var Wet = ee.FeatureCollection(fieldObs.filter(ee.Filter.eq('water_stat', 'Wet')));
    print(Wet)

The more elegant solution was provided by Noel Gorelick:

Map over the features, give each feature a "style" dictionary containing a >"color" property based on its status.
Then call collection.style(), passing the name of the style dictionary >property. See this example: https://code.earthengine.google.com/a9ba80f9d412c918f3499261f5d435e7

In Noel's method, the entire FeatureCollection can be added as a single layer, with unique colors based on feature properties. Just what I was looking for.

Answer 2

This is essentially the same as Noel's method mentioned by Anson, but less verbose. Instead of creating a new feature, I just set the properties of the old feature.

// make a feature collection and add to map
var fc = ee.FeatureCollection([
  ee.Feature(ee.Geometry.Point([0,0]), {class: 0}),
  ee.Feature(ee.Geometry.Point([0,1]), {class: 1})
])
Map.addLayer(fc, {}, 'no color')
Map.centerObject(fc)

// function to conditionally set properties of feature collection
var setPointProperties = function(f){ 
  var klass = f.get("class") // 0 or 1
  var mapDisplayColors = ee.List(['0000ff', 'ff0000']); // class 0 should be blue, class 1 should be red
  
  // use the class as index to lookup the corresponding display color
  return f.set({style: {color: mapDisplayColors.get(klass)}})
}

// apply the function and view the results on map
var styled = fc.map(setPointProperties)
Map.addLayer(styled.style({styleProperty: "style"}), {}, 'conditionally styled')

https://code.earthengine.google.com/?scriptPath=users%2Fcaseyengstrom%2Freprex%3AconditionallyStyleFeatures