AI-generated Key Takeaways
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The
map
function applies an algorithm to each element of a collection. -
It returns a new collection containing the results of the algorithm applied to each original element.
-
An optional argument
dropNulls
allows for removing elements where the algorithm returns null.
Returns the mapped collection.
Usage | Returns |
---|---|
FeatureCollection.map(algorithm, dropNulls) | Collection |
Argument | Type | Details |
---|---|---|
this: collection | Collection | The Collection instance. |
algorithm | Function | The operation to map over the images or features of the collection. A JavaScript function that receives an image or features and returns one. The function is called only once and the result is captured as a description, so it cannot perform imperative operations or rely on external state. |
dropNulls | Boolean, optional | If true, the mapped algorithm is allowed to return nulls, and the elements for which it returns nulls will be dropped. |
Examples
Code Editor (JavaScript)
// FeatureCollection of power plants in Belgium. var fc = ee.FeatureCollection('WRI/GPPD/power_plants') .filter('country_lg == "Belgium"'); // Function to convert power plant capacity from megawatts to gigawatts and // add the value as a new feature property. var mwToGw = function(feature) { var megawatt = feature.getNumber('capacitymw'); var gigawatt = megawatt.divide(1000); return feature.set('capacitygw', gigawatt); }; // Apply the function to each feature in the collection. fc = fc.map(mwToGw); print('Note the new "capacitygw" property in each feature', fc);
import ee import geemap.core as geemap
Colab (Python)
# FeatureCollection of power plants in Belgium. fc = ee.FeatureCollection('WRI/GPPD/power_plants').filter( 'country_lg == "Belgium"') # Function to convert power plant capacity from megawatts to gigawatts and # add the value as a new feature property. def mw_to_gw(feature): megawatt = feature.getNumber('capacitymw') gigawatt = megawatt.divide(1000) return feature.set('capacitygw', gigawatt) # Apply the function to each feature in the collection. fc = fc.map(mw_to_gw) print('Note the new "capacitygw" property in each feature:', fc.getInfo())