Google Earth Engine - add label to feature collection table/CSV

Question

I'm exploring different ocean environmental data in Google Earth Engine.

I have created an image per variable by using the .reduce(ee.Reducer.mean()) function.

var sstHS_mean = sstHS_collection.reduce(ee.Reducer.mean());

I have several areas that I'm interested in comparing and have used the .reduceRegions function to reduce into a feature collection to find the mean score for each area I'm interested in.

var sstHS_region = sstHS_mean.reduceRegions({
reducer: ee.Reducer.mean(),
collection: reefsEdit,
scale: 30});

I realised I could combine feature collections and export as a CSV. Using this code.

var sal_sst_HS = ee.FeatureCollection([sstHS_region, salHS_region,]).flatten();

I can then export this as a CSV which produces this table

However, it's not clear which data comes from. Is there anyway of adding a label to each image or feature collection so I can identify it when I export the table? Maybe in place of the 0 and 1 seen under system:index or in a new column I could label?

Answer 1

You can add a property to all the features of each collection that designates where the reduction came from.

Here, I .set() a column name called 'variable' to each feature in both feature collections. For sstHS_region features, I set the variable name as 'sstHS' and for the salHS_region features I set the variable name as 'salHS'.

sstHS_region = sstHS_region.map(function(feature) {
  return feature.set('variable', 'sstHS')
});

salHS_region = salHS_region.map(function(feature) {
  return feature.set('variable', 'salHS')
})

You can also .add(ee.Image.constant(1)).rename('Variable') a band to each of the data images that your are reducing - when you do the reduction the codified variable will be included in the returned feature collection.