AI-generated Key Takeaways
-
The
mapfunction 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
dropNullsallows 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 ) display ( 'Note the new "capacitygw" property in each feature:' , fc )
