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I applied a spatial join to two feature collections and am trying to extract specific properties from one in order to append them to another.

In order to retrieve a property from one of the features, I had to go through a convoluted process that I'm not sure I will be able to map accurately (see second block).

Is there a better way to do this?

I followed this link closely. For clarity, what I hope for is to add the HUC ID to the myPoints featureCollection as another property in the following code:

var HUC = ee.FeatureCollection("USGS/WBD/2017/HUC10");
var myPoints = ee.FeatureCollection("users/seancliffcarter/fishPrecenseNoNA");



//Define a filter where the points intersect the HUC
var distFilter = ee.Filter.intersects({
  leftField: '.geo', 
  rightField: '.geo', 
  maxError: 10
});

//Save the HUC object as a property named 'HUC'
var distSaveAll = ee.Join.saveAll({
  matchesKey: 'HUC',
});

//Apply the join
var spatialJoined = distSaveAll.apply(myPoints,HUC,distFilter);

This works great, except that each feature within spatialJoined now contains a HUC object as a property, but I'd like to extract the ID (or something similar) from each.

A basic sanity check starts to break down:

//Select an arbitrary feature to troubleshoot
var testFeature = spatialJoined.first();

//Select the HUC property within the feature
var testHUC = ee.Feature(testFeature.get('HUC'));

//This is where I'm struggling. Is testHUC a feature or a list? I casted it to a Feature, correct?

//Implies that testHUC is a "list" object:
print(testHUC,"Test HUC");

//Implies that testHUC is a "feature":
print(testHUC.name())

//If testHUC is a "feature", I should be able to use .get():

var testHUCName = testHUC.get('name');

//Gives Invalid type error



//Assuming it is a list, I can use the following code to extract a property. 
//First cast to list:
var featureList = ee.List(testFeature)

//Then retrieve first element and recast to a feature?:
var firstElement = ee.Feature(featureList.get(0))

//Finally get the ID property:

var hucID = firstElement.get('ID');
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1 Answer 1

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If you are confused with the data types of your objects, you can always use print. print(spatialJoined.first()); gave the following result:

enter image description here

Line marked 1 is a ee.Feature(), 2 is ee.List() and 3 is ee.Feature(). So just cast the datatypes in that order if you want to access the id property.

Lastly, id is actually stored as system:index for ee.Feature() objects. More details about that here.

So putting it all together, just replace your second code chunk with the following lines:

/// adding id property of HUC feature to root feature
var spatialJoined = spatialJoined.map(function(feature){
  var hucid = ee.Feature(ee.List(feature.get("HUC")).get(0)).get("system:index");
  var feature = feature.set('HUCid',hucid);
  return feature
})

This link has the complete working solution.

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