Exporting multiple tables to Drive Earth Engine

Question

I have a list of FeatureCollections that I want to export all at once (instead of writing out the export module multiple times) using Javascript API. I have seen the posts by @Rodrigo E Principe such as here and others like this one showing the use of normal JS loops (admittedly the second link is for exporting to asset).

I am trying to do the exact same thing as the first link, just exporting a FeatureCollection instead of an ImageCollection. However, when I run the code I get no tasks to run nor am I getting any errors. I don't understand what's happening.

Here is my code:

// Make a list of Features.
var features = [
  ee.Feature(ee.Geometry.Point(97.58, 24.36), {name: 'sample1'}),
  ee.Feature(ee.Geometry.Point(99.45, 20.26), {name: 'sample2'}),
  ee.Feature(ee.Geometry.Point(93.24, 21.42), {name: 'sample3'}),
  ee.Feature(ee.Geometry.Point(96.13, 24.12), {name: 'sample4'}),
  ee.Feature(ee.Geometry.Point(96.88, 22.48), {name: 'sample5'})
];

// Create a FeatureCollection from the list and print it.
var points = ee.FeatureCollection(features);
print(points);

var l8sr = ee.ImageCollection('LANDSAT/LC08/C01/T1_SR')
                  .filterDate('2015-06-23', '2020-01-31')
                  .filterBounds(points);
print("Landsat", l8sr)


var index = ee.List.sequence(0,4)
var coords = points.geometry().coordinates()
print('coords', coords)

// do this for each index
var test1 = index.map(function(q){
    var sub = l8sr.filterBounds(ee.Geometry.Point(coords.get(q)))
    return sub
});

//run test for first one
var firstcoll = ee.ImageCollection(test1.get(0))
var img = firstcoll.first();
var bands = img.bandNames()

//get the value for each band for every image
var loop = index.map(function(ind){
  var getvals = function(img1){
    var date = img1.date().format('yyyy-MM-dd')
    var value = img1.select(bands)
   .reduceRegion(ee.Reducer.first(), ee.Geometry.Point(coords.get(ind)))
   return ee.Feature(ee.Geometry.Point(coords.get(ind)), {value: value, date: date})
  };
var newft = firstcoll.map(getvals);
return(newft);
});

print('loopresult', loop)
print('loop ex', ee.FeatureCollection(loop.get(0)))

// loop on client side
for (var i = 0; i<loop.length;i++) {
  var toexport = ee.FeatureCollection(loop.get(i));
  var nam = "test_point_" + i

      // Export
Export.table.toDrive(
  {collection: toexport,
  description: nam,
  folder: "dissertation",
  fileNamePrefix: nam,
  selectors: ['B1','B2','B3','B4','B5','B6','B7','B10','B11',
  'pixel_qa', 'radsat_qa', 'sr_aerosol']
  });
}

Answer 1

You need to get the loop variables on the client-side. Thus, use getInfo() or evaluate() in this line (51):

for (var i = 0; i<loop.getInfo().length;i++) 

or probably a bit more efficient

for (var i = 0; i<loop.size().getInfo();i++) 

or with evaluate:

loop.size().evaluate(function(sizeCol){
  // loop on client side
  for (var i = 0; i<sizeCol;i++) {

   ........
}

If you now the number of featureCollections you want to export prior, you could also just hard code that value. Also, you might want to set the variable value as a dictionary to the feature collection. See line 41: link, or with evaluate link2