Aggregating properties over features, and handling null using Google Earth Engine?

Question

I have a FeatureCollection where I would like to take the mean of multiples properties for each feature.

I did not find so far an elegant way to do this, currently I am using using the map function, mapping over each feature a number operation like: var1.add(var).divide(2).

Is there a more elegant way to aggregate over properties in a featureCollection? The problem with my solution is that I can't handle null values, which unfortunately happen often in my dataset. Indeed, using the add() function will fail in that case, see example below.

Code: https://code.earthengine.google.com/9944b02bc720859307811571fcc3cb0e

 var features = ee.FeatureCollection([
  ee.Feature(null, {var1: 1, var2: 2}),
  ee.Feature(null, {var1: 2, var2: 3}),
  ee.Feature(null, {var1: 1, var2: null})]);

print(features)


/// mean
var getMean = function(feature) {
  var var1 = ee.Number(feature.get('var1'));
  var var2 = ee.Number(feature.get('var2'));


  return feature.set({mean: var1.add(var2).divide(5)});
}


// Works:
var test_agg = features.limit(2).map(getMean);
print(test_agg)

// Does not work:
var test_agg2 = features.map(getMean);
print(test_agg2)

Answer 1

I've made a function to perform that task on the Code Editor. Source code can be found here: https://earthengine.googlesource.com/users/fitoprincipe/geetools/+/master

How to use it:

var tools = require('users/fitoprincipe/geetools:tools')

var f1 = ee.Feature(null, {var1: 1, var2: 2, numprop:4})
var f2 = ee.Feature(null, {var1: 2, var2: 3, strprop: 'jojo'})
var f3 = ee.Feature(null, {var1: 1, var2: null})

var features = ee.FeatureCollection([f1, f2, f3]);

print(features)

// The function we are going to use is called `aggregate_properties`

// Sum over a FeatureCollection
var sum_col = features.map(tools.aggregate_properties({
  properties:['var1', 'var2'],
  reducer: 'sum',
  name: 'sum'
}))
print(sum_col)

// Mean over a FeatureCollection
var mean_col = features.map(tools.aggregate_properties({
  properties:['var1', 'var2'],
  reducer: 'mean',
  name: 'custom_name'
}))
print(mean_col)

// Mean over one feature
var mean_feat = tools.aggregate_properties({
  name: 'mean_one_feature'
})(f1)
print(mean_feat)

link: https://code.earthengine.google.com/2ecbedacfc1f8a566025147c00f35077