javascript - 在 Earth Engine Javascript API 中按 ID 加入两个要素集合

Question

我只是想以这种方式加入两个集合，加入的特征集合具有主要和次要特征集合的所有属性。

// Create the primary collection.
var primaryFeatures = ee.FeatureCollection([
  ee.Feature(null, {foo: 0, ID: 'a'}),
  ee.Feature(null, {foo: 1, ID: 'b'}),
  ee.Feature(null, {foo: 1, ID: 'c'}),
  ee.Feature(null, {foo: 2, ID: 'd'}),
]);

// Create the secondary collection.
var secondaryFeatures = ee.FeatureCollection([
  ee.Feature(null, {bar: 1, ID: 'a'}),
  ee.Feature(null, {bar: 1, ID: 'b'}),
  ee.Feature(null, {bar: 2, ID: 'c'}),
  ee.Feature(null, {bar: 3, ID: 'd'}),
]);

// Use an equals filter to specify how the collections match.
var toyFilter = ee.Filter.equals({
  leftField: 'ID',
  rightField: 'ID'
});

// Define the join.
var innerJoin = ee.Join.simple()

// Apply the join.
var toyJoin = innerJoin.apply(primaryFeatures, secondaryFeatures,  toyFilter);


// Print the result.
print('Inner join toy example:', toyJoin);

最终的 toyJoin 特征集合应该有 5 个特征和 3 个属性 ID、foo 和 bar。非常感谢!

Answer 1

我不希望输出中有 5 个特征，因为您只有四个唯一 ID，并且输入集合中的 ID 之间是 1:1 的关系。无论如何，要获得内部联接，请使用 ee.Join.inner()。要合并结果，映射内部连接:

// Create the primary collection.
var primaryFeatures = ee.FeatureCollection([
  ee.Feature(null, {foo: 0, ID: 'a'}),
  ee.Feature(null, {foo: 1, ID: 'b'}),
  ee.Feature(null, {foo: 1, ID: 'c'}),
  ee.Feature(null, {foo: 2, ID: 'd'}),
]);

// Create the secondary collection.
var secondaryFeatures = ee.FeatureCollection([
  ee.Feature(null, {bar: 1, ID: 'a'}),
  ee.Feature(null, {bar: 1, ID: 'b'}),
  ee.Feature(null, {bar: 2, ID: 'c'}),
  ee.Feature(null, {bar: 3, ID: 'd'}),
]);

// Use an equals filter to specify how the collections match.
var toyFilter = ee.Filter.equals({
  leftField: 'ID',
  rightField: 'ID'
});

// Define the join.
var innerJoin = ee.Join.inner();

// Apply the join.
var toyJoin = innerJoin.apply(primaryFeatures, secondaryFeatures,  toyFilter);

// Print the result.
print('Inner join toy example:', toyJoin);

print(toyJoin.map(function(pair) {
  var f1 = ee.Feature(pair.get('primary'));
  var f2 = ee.Feature(pair.get('secondary'));
  return f1.set(f2.toDictionary());
}));