Google Earth Engine – Adding Property to ee.Feature Based on Another Property

google-earth-engine

I have a featureCollection that contains a string property called 'TaxOrder'. In total there are 12 different possible TaxOrders (['Alfisols', 'Andisols', 'Aridisols', ...]).

I want to add the number of each TaxOrder (i.e. a number between 1 and 12) to each feature relative to the TaxOrder, e.g. if the TaxOrder is 'Alfisols', add {taxOrderNum: 1} as a property.

I've figured out a very lengthy way of doing this, so I am thinking there must be a simpler way of doing it, using .remap() for example (but without actually replacing the values of an existing property).

// Remove areas with null TaxOrder
USDA_Soils = USDA_Soils.filterMetadata('TaxOrder', 'not_equals', '');
print(USDA_Soils.limit(100));

// Function to add number corresponding to tax order
var addTaxOrderNum = function(feat) {
  var result = ee.Algorithms.If({
    condition: ee.String(feat.get('TaxOrder')).equals('Alfisols'),
    trueCase: feat.set({taxOrderNum: 1}),
    falseCase: ee.Algorithms.If({
      condition: ee.String(feat.get('TaxOrder')).equals('Andisols'),
      trueCase: feat.set({taxOrderNum: 2}),
      falseCase: ee.Algorithms.If({
        condition: ee.String(feat.get('TaxOrder')).equals('Aridisols'),
        trueCase: feat.set({taxOrderNum: 3}),
        falseCase: ee.Algorithms.If({
          condition: ee.String(feat.get('TaxOrder')).equals('Entisols'),
          trueCase: feat.set({taxOrderNum: 4}),
          falseCase: ee.Algorithms.If({
            condition: ee.String(feat.get('TaxOrder')).equals('Gelisols'),
            trueCase: feat.set({taxOrderNum: 5}),
            falseCase: ee.Algorithms.If({
              condition: ee.String(feat.get('TaxOrder')).equals('Histosols'),
              trueCase: feat.set({taxOrderNum: 6}),
              falseCase: ee.Algorithms.If({
                condition: ee.String(feat.get('TaxOrder')).equals('Inceptisols'),
                trueCase: feat.set({taxOrderNum: 7}),
                falseCase: ee.Algorithms.If({
                  condition: ee.String(feat.get('TaxOrder')).equals('Mollisols'),
                  trueCase: feat.set({taxOrderNum: 8}),
                  falseCase: ee.Algorithms.If({
                    condition: ee.String(feat.get('TaxOrder')).equals('Oxisols'),
                    trueCase: feat.set({taxOrderNum: 9}),
                    falseCase: ee.Algorithms.If({
                      condition: ee.String(feat.get('TaxOrder')).equals('Spodosols'),
                      trueCase: feat.set({taxOrderNum: 10}),
                      falseCase: ee.Algorithms.If({
                        condition: ee.String(feat.get('TaxOrder')).equals('Ultisols'),
                        trueCase: feat.set({taxOrderNum: 11}),
                        falseCase: ee.Algorithms.If({
                          condition: ee.String(feat.get('TaxOrder')).equals('Vertisols'),
                          trueCase: feat.set({taxOrderNum: 12}),
                          falseCase: feat
                        })
                      })
                    })
                  })
                })
              })
            })
          })
        })
      })
    })
  });
  return result;
};

// Map function over featureCollection
var USDA_Soils_Final = USDA_Soils.map(addTaxOrderNum);
print(USDA_Soils_Final.limit(100));

https://code.earthengine.google.com/b00826b5d9ed0d12811389c7b511bd8d

Best Answer

A general rule for this kind of problem is to express your repetitive structure as data, not code. A mapping from one value to another is a kind of data that can be stored in a dictionary.

So, first define a dictionary. (This can be done more cleverly to not have to list the numbers explicitly, but let's keep things simple.)

var taxOrders = ee.Dictionary({
  'Alfisols': 1,
  'Andisols': 2,
  'Aridisols': 3,
  'Entisols': 4,
  'Gelisols': 5,
  'Histosols': 6,
  'Inceptisols': 7,
  'Mollisols': 8,
  'Oxisols': 9,
  'Spodosols': 10,
  'Ultisols': 11,
  'Vertisols': 12,
});

Then, use that dictionary inside the feature mapping function.

var addTaxOrderNum = function(feature) {
  var taxOrderNum = taxOrders.get(feature.get('TaxOrder'));
  return feature.set('taxOrderNum', taxOrderNum);
};

https://code.earthengine.google.com/423c5b4f30b3928c57b8ec9413912bf2

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