Google Earth Engine – How to Rename Columns in FeatureCollection

errorfeaturesgoogle-earth-engine

I have a Feature Collection I'm exporting as a csv. I used the reduceRegions function to get mean values of several different variables per region, and merged these into one large FeatureCollection. I simply want to chnage the column/property name for one of these. I found you could use the select function, but I have to rename one but still all the columns in as otherwise the selec function removes them from the FeatureCollection.

//var Dat = Dat.select(['mean', 'id'], ['SE_score', 'id']);

However, I'm getting this error

FeatureCollection (Error)
Error in map(ID=7_PB_IleDiamant_Lagoon): Feature.select: Selected a different number of properties (1) than names (2).

I think this is because I don't actually have data for some of these variables, they're just blank, which is fine for my export, but it means it's not allowing me to change the property name from 'mean' to 'SE_score'.

Are there other methods for changing column/property names you're aware of?

Best Answer

You could try:

var DataRenamed = Data.map(function(feat){
  return ee.Feature(feat.geometry(), { 
    SE_score: feat.get('mean'),
    id: feat.get('id')
  })
})

If you don't want or need the geometry, change feat.geometry() to null

Make sure that when you export the table, you set the selectors property. Otherwise you might have the change that a property with null values is not exported.

Export.table.toDrive({
           collection: DataRenamed, 
           description: 'NAME', 
           fileFormat: 'CSV', 
           selectors: ['SE_score', 'id']})

Related Solutions

[GIS] How to visualize points in a FeatureCollection based on feature properties using Google Earth Engine

The Google Earth Engine Developers group just provided two solutions - one quick fix and one more elegant.

The quick fix - filter out the "wet" features, then add those as a unique layer. Then filter out the "dry" features, and add those as a second layer. Here's the code used to filter out wet features:

    var Wet = ee.FeatureCollection(fieldObs.filter(ee.Filter.eq('water_stat', 'Wet')));
    print(Wet)

The more elegant solution was provided by Noel Gorelick:

Map over the features, give each feature a "style" dictionary containing a >"color" property based on its status.
Then call collection.style(), passing the name of the style dictionary >property. See this example: https://code.earthengine.google.com/a9ba80f9d412c918f3499261f5d435e7

In Noel's method, the entire FeatureCollection can be added as a single layer, with unique colors based on feature properties. Just what I was looking for.

Google Earth Engine – How to Fix reduceRegions Is Not a Function Error

reduceRegions is a method of an Image not an ImageCollection and winter_day_C is an ImageCollection, not an Image.

If you want to reduce spatially to create a single mean value per city by image (date), then map reduceRegions to each image in the ImageCollection.

// Import day and night time land surface temperature (LST) by season from MODIS
var modis = ee.ImageCollection("MODIS/006/MOD11A1");

// WINTER.  
var winter_day = modis.filter(ee.Filter.date('2009-12-01', '2010-03-01')).select('LST_Day_1km');

// Convert to Celsius. 
var winter_day_C = winter_day.map(function(image) {
  return image
    .multiply(0.02)
    .subtract(273.15)
    .reduceRegions({  // <---- reduceRegions on the Image object
      collection: cities,
      reducer: ee.Reducer.mean(),
      scale: 100,
    })
    .copyProperties(image, ['system:time_start']);
});

To avoid the "Error: Unable to use a collection in an algorithm that requires a feature or image. This may happen when trying to use a collection of collections where a collection of features is expected;" do what the error tells you to and "use flatten, or map a function to convert inner collections to features."

// Export 
Export.table.toDrive({
  collection: winter_day_C.flatten(),  // <----- flatten()
  description: '2010_WinterDayLST_export',
  fileFormat: 'CSV'
});

Best Answer

Related Solutions

[GIS] How to visualize points in a FeatureCollection based on feature properties using Google Earth Engine

Google Earth Engine – How to Fix reduceRegions Is Not a Function Error

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