7

I'm trying to extract values from a FeatureCollection as a list. Here's some example code that I'm using in Earth Engine's code editor:

var viirs = 
    ee.Image('NOAA/VIIRS/DNB/MONTHLY_V1/VCMCFG/20120401').select('avg_rad');

var maineCounties = 
    ee.FeatureCollection('ft:1S4EB6319wWW2sWQDPhDvmSBIVrD3iEmCLYB7nMM'). 
    filter(ee.Filter.eq('StateName', 'Maine'));

var maineMeansFeatures = viirs.reduceRegions({
  collection: maineCounties,
  reducer: ee.Reducer.mean(),
  scale: 30
});

The "maineMeansFeatures" FeatureCollection has a column called "mean" -- I trying to extract the values in "mean" as a list (so, here, it'd be a list of 16 values -- one for each feature).

Any ideas on how to do this? (Note: I'm very new to javascript so I'm not that familiar with FeatureCollections).

8

Take a look at ee.FeatureCollection.aggregate_array:

Aggregates over a given property of the objects in a collection, calculating a list of all the values of the selected property.

So

maineMeansFeatures.aggregate_array("mean") 

should bring you an array of "means".

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  • 1
    For those coming to this question (as I was) trying to get the list of unique values of Feature properties within a FeatureCollection, then use the .distinct() method on the FeatureCollection before using the .aggregate_array(): mainMeansFeatures.distinct("mean").aggregate_array("mean"); Note this would make more sense with categorical properties rather than float (in which case they are likely to all be unique!)
    – mikoontz
    May 21 at 14:20

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