Sorry if this is an silly question, as I am starting to work with GEE.

I am iterating (mapping) over a Sentinel-2 image collection, using different coordinates and dates in each step.

My goal is to download the mean band properties of the available images in each step, but I want to "join" the FeatureCollections obtained in each step to avoid downloading multiple files.

How should I proceed?

Here is some code example:

var S2 = ee.ImageCollection("COPERNICUS/S2");

// List with LAT, LON, and dates

var list = [
[42.454,3.543, '2017-05-23','2017-06-24'],
[42.7,3.8, '2018-04-19','2018-05-20'],

var loop = function(point)
  var x = point[1];
  var y = point[0];
  var date0 = point[2];
  var date1 = point[3];
  var point = ee.Geometry.Point([x,y]);

  var S2TemporalFiltered = S2.filterDate(date0,date1);
  var S2SpatialFiltered = S2TemporalFiltered.filterBounds(point);

  //Box coordinates to reduce collection
  var x1 = x - 0.002;
  var x2 = x + 0.002;
  var y1 = y - 0.001;
  var y2 = y + 0.001;
  var box = ee.Geometry.Rectangle(x1,y1,x2,y2);

  //Cutting collection to box
  var S2Clipped = S2SpatialFiltered.map(
    function(img) {return img.clip(box)}

  //Mean values
  var eBox = ee.Feature(box);
  var func = function(image){
    var meanList1 = image.reduceRegion({
      reducer: ee.Reducer.mean(),
      geometry: eBox.geometry(),
    return ee.Feature(null, meanList1);
  var total = S2Clipped.map(func);

//Now I need to add "total" to a "matrix" where 
// band properties will be added in each step of the loop.
//Each line relates to an image

//This next part should be out of the loop, dowloading all images properties 
//at once (instead of having two files, I would have one file with two rows) 

collection: total,
description: 'Total',
fileFormat: 'CSV',


var a = list.map(loop)

1 Answer 1


Your function(point) does not return a value, therefore you cannot access nor merge the collection outside the function.

Add this at the end of your function(point) to return a value:

return S2Clipped.map(func);

You can then access the featurecollection outside your function and merge them together using:

var a = ee.FeatureCollection(list.map(loop)).flatten()


And export the full colleciton using:

collection: a,
description: 'Total',
fileFormat: 'CSV',

link script


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