Page Summary
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Creates a join between a primary and secondary collection.
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Returns elements from the primary collection that have a match in the secondary collection.
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No additional properties are added to the results of the join.
| Usage | Returns |
|---|---|
ee.Join.simple()
|
Join |
No arguments.
Examples
Code Editor (JavaScript)
// 1. Simple Join by Attribute Match an an ee.FeatureCollection // This example selects features in one collection that have a matching // attribute in another collection. var primaryFeatures = ee . FeatureCollection ([ ee . Feature ( null , { id : 1 , name : 'Forest' }), ee . Feature ( null , { id : 2 , name : 'Water' }), ee . Feature ( null , { id : 3 , name : 'Urban' }), ee . Feature ( null , { id : 4 , name : 'Shrub' }) ]); var secondaryFeatures = ee . FeatureCollection ([ ee . Feature ( null , { type_id : 1 , label : 'Natural' }), ee . Feature ( null , { type_id : 2 , label : 'Natural' }) ]); // Define the filter: match 'id' from primary to 'type_id' from secondary. var filter = ee . Filter . equals ({ leftField : 'id' , rightField : 'type_id' }); // Create the simple join. var simpleJoin = ee . Join . simple (); // Apply the join. Only 'Forest' and 'Water' (IDs 1 and 2) will remain. var attributeResult = simpleJoin . apply ( primaryFeatures , secondaryFeatures , filter ); print ( 'Attribute Join Result:' , attributeResult ); // 2. ee.Join.simple on an ee.ImageCollection // Define a primary collection of Sentinel-2 images. var primary = ee . ImageCollection ( 'COPERNICUS/S2_SR_HARMONIZED' ) . filterDate ( '2023-06-01' , '2023-07-01' ) . filterBounds ( ee . Geometry . Point ([ - 122.3 , 37.7 ])); // Define a secondary collection representing a specific event or criteria. // In this case, we filter to images that have a very low cloud cover percentage. var secondary = primary . filter ( ee . Filter . lt ( 'CLOUDY_PIXEL_PERCENTAGE' , 1 )); // Define the join condition. Here we match by the 'system:index' property. var filter = ee . Filter . equals ({ leftField : 'system:index' , rightField : 'system:index' }); // Create the simple join. var simpleJoin = ee . Join . simple (); // Apply the join to filter the primary collection. var joinedCollection = simpleJoin . apply ( primary , secondary , filter ); print ( 'Original count:' , primary . size ()); print ( 'Filtered count (only low cloud images):' , joinedCollection . size ()); // 3. FeatureCollection Spatial Filtering // Common use case: Keep only the features in a primary collection that // intersect with a secondary collection of polygon boundaries. var states = ee . FeatureCollection ( 'TIGER/2018/States' ); var region = ee . Geometry . Point ([ - 98.57 , 39.82 ]). buffer ( 500000 ). bounds (); var pointsOfInterest = ee . FeatureCollection ( 'WRI/GPPD/power_plants' ) . filterBounds ( region ); // Find states that contain at least one power plant within the defined region var statesWithPlants = ee . Join . simple (). apply ({ primary : states , secondary : pointsOfInterest , condition : ee . Filter . intersects ({ leftField : '.geo' , rightField : '.geo' }) }); Map . centerObject ( region , 5 ); Map . addLayer ( region , { color : 'purple' }, 'Region' ); Map . addLayer ( states , { color : 'gray' }, 'All States' , true , 0.5 ); Map . addLayer ( statesWithPlants , { color : 'red' }, 'States with Power Plants' ); Map . addLayer ( pointsOfInterest , { color : 'blue' }, 'Power Plants' );
