Unable to encode List data type as attribute when export FeatureCollection

Question

var FC = ee.FeatureCollection([
  ee.Feature(ee.Geometry.Point(120, 0), {'instrumentMode': ['IW', 'EW']})
  ]);
print('FC', FC);
Export.table.toAsset(FC)

When I tried to export this table, I confronted the error message, saying that "Unable to encode value 'instrumentMode' of feature 0: invalid type". I am confuse why making a list as a atribute does not work?

Answer 1

Look at this thread from the developer forum: https://groups.google.com/d/topic/google-earth-engine-developers/8E9o83kUtmk/discussion

EE is picky on the type of properties for assets. You probably have to stringify the list:

var FC = ee.FeatureCollection([
  ee.Feature(ee.Geometry.Point(120, 0), {
    'instrumentMode': JSON.stringify(['IW', 'EW'])
  })
  ]);
print('FC', FC);
Export.table.toAsset(FC)

Then decode it when reading it:

var instrumentMode = ee.FeatureCollection('users/wiell/myExportTableTask')
  .first()
  .getString('instrumentMode')
  .decodeJSON()
print(instrumentMode)  

Answer 2

Use server ee.String.encodeJSON() instead of client JSON.stringify() to stringify any structured properties inside a map().

var list = ee.List(['IW', 'EW']);
var FC = ee.FeatureCollection([
  ee.Feature(ee.Geometry.Point(120, 0), { "instrumentMode":ee.String.encodeJSON(list) })
  ]);
print('FC', FC);
Export.table.toAsset(FC)

It exports a feature containing prop {"instrumentMode":["IW","EW"]}