Google Earth Engine – Reformatting Dictionary Object to Rows and Columns

csvdictionarygoogle-earth-engine

I'm new to javascript & GEE, trying to reduce a global FeatureCollection by computing sums of two specific properties, grouped by country (using this helpful link). The output is a Dictionary Object that contains all the info I need.

I'd like to reformat the data into rows and columns and then export it as a CSV.

What is the simplest way to do this?

// Call up WDPA data, filter

var dataset = ee.FeatureCollection('WCMC/WDPA/current/polygons')
              .filter(ee.Filter.or(
              ee.Filter.and(ee.Filter.eq('MARINE','0'),
                            ee.Filter.eq('IUCN_CAT','Ia')),
              ee.Filter.and(ee.Filter.eq('MARINE','0'),
                            ee.Filter.eq('IUCN_CAT','Ib'))));

// Compute sums of protected area, grouped by country

var sums = dataset
  .filter(ee.Filter.and(
    ee.Filter.neq('GIS_AREA', null),
    ee.Filter.neq('REP_AREA', null)))
  .reduceColumns({
    selectors: ['REP_AREA', 'GIS_AREA', 'PARENT_ISO'],
    reducer: ee.Reducer.sum().repeat(2).group({
      groupField: 2,
      groupName: 'country',
    })
});

print(sums);

I can export as a CSV from there, but it obviously comes out in Dictionary form (i.e. not terribly useful in a spreadsheet). This post almost addresses the question, but their initial output is a FeatureCollection, and mine is an Object. I couldn't get the chosen answer to work for me, and I'm just going in circles.

Best Answer

This may not be the only way to do it, but it works:

/** YOUR CODE **/
// Call up WDPA data, filter

var dataset = ee.FeatureCollection('WCMC/WDPA/current/polygons')
              .filter(ee.Filter.or(
              ee.Filter.and(ee.Filter.eq('MARINE','0'),
                            ee.Filter.eq('IUCN_CAT','Ia')),
              ee.Filter.and(ee.Filter.eq('MARINE','0'),
                            ee.Filter.eq('IUCN_CAT','Ib'))));

// Compute sums of protected area, grouped by country

var sums = dataset
  .filter(ee.Filter.and(
    ee.Filter.neq('GIS_AREA', null),
    ee.Filter.neq('REP_AREA', null)))
  .reduceColumns({
    selectors: ['REP_AREA', 'GIS_AREA', 'PARENT_ISO'],
    reducer: ee.Reducer.sum().repeat(2).group({
      groupField: 2,
      groupName: 'country',
    })
});

print(sums);

/** MY ANSWER **/
var groups = ee.List(sums.get('groups'));

var fc = ee.FeatureCollection(groups.map(function(obj) {
  var object = ee.Dictionary(obj)
  var name = ee.String(object.get('country'))
  var sum = ee.List(object.get('sum'))
  var rep = ee.Number(sum.get(0))
  var gis = ee.Number(sum.get(1))
  return ee.Feature(null, {'name':name, 'rep_area':rep, 'gis_area':gis})
}))

print(fc.limit(1))

Export.table.toDrive({
  collection: fc, 
  description: 'description', 
  folder: 'FOLDER', 
  fileNamePrefix: 'NAME', 
  fileFormat: 'CSV',
})
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