Reducing ee.Image to a list and then exporting as CSV file

Question

I am struggling with transforming a single image to a list and then exporting it to my drive.

I am using the ee.Reducer.toList() but the output looks like this:

Insted of this:

When I print the featureCollection that is to be written to the file - it seems to contain all the data needed.

Here is my code:

var region = ee.Geometry.Polygon([
  [[-5, 40], [-5, 60], [-5, 60]]
]);

//Dates of Interest
var start = ee.Date("2018-04-01");
var finish = ee.Date("2018-05-01");

var sen2 = ee.ImageCollection('COPERNICUS/S2_SR')
  .filterDate(start,finish)
  .filterBounds(region)
  .map(function(image){
    return image
    .clip(region)
    .normalizedDifference(['B8','B4'])
    .rename('NDVI')
  })

print(sen2)

var sngl = ee.Image(sen2.first())

var list = sngl.reduceRegion({
  reducer: ee.Reducer.toList(),
  geometry: region,
  maxPixels: 1e8,
  scale: 10
});

// Make a feature without geometry and set the properties to the dictionary of means.
var feature = ee.Feature(null, list);

// Wrap the Feature in a FeatureCollection for export.
var featureCollection = ee.FeatureCollection([feature]);

print(featureCollection)

// Export the FeatureCollection.
Export.table.toDrive({
  collection: featureCollection,
  fileNamePrefix: 'field_test',
  folder: 'field_test',
  fileFormat: 'CSV'
});

Any ideas?

Answer 1

When you export a table, each row is a feature. Your code is making a collection with exactly one feature in it; you need to produce many features instead. Also, your variable 'list' is misnamed as it is a dictionary containing a list, not a list.

So, changing this section of your code will get you a table shaped like you are asking for:

var list = ee.List(sngl.reduceRegion({
  reducer: ee.Reducer.toList(),
  geometry: region,
  scale: 10
}).get('NDVI'));

var featureCollection = ee.FeatureCollection(list.map(function (ndviValue) {
  return ee.Feature(null, {'NDVI': ndviValue});
}));

https://code.earthengine.google.com/1041cd6787dd04dc81d8725aa14af356

The map on the list converts the list of numbers to a list of Features, and then can be converted to a FeatureCollection for export.