[GIS] Arrays from feature collections in Google Earth engine

arraygoogle-earth-engine

I need to convert a Feature Collection containing only numeric data to a 2D matrix. I have written the following code however it gives matA as a list of arrays despite explicit type conversion, here table is my feature collection and data is the list of properties I need to extract into the matrix

// list of data to extract from FC
var data=ee.List(['bio01','bio02','bio03','bio04','bio05','bio06','bio07',
              'bio08','bio09','bio10','bio11','bio12','bio13','bio14',            
       'bio15','bio16','bio17','bio18','bio19','dem','tmax','tmin','prec']);

//data becomes the list from which the user wants to remove the ones he doesn't need

var tableArray=table.toList(200,0)  // list of features

var tableList=ee.List(tableArray.map(function(element){
  var feat=ee.Feature(element)  
  var array=feat.toArray(data)  //feature to array
  return ee.List(array) //array to list 
}))

// array needs all elements of list only not array inside list so we change feature to list

var matA=ee.Array(tableList)

print(matA)

The error I am getting is:

Array (Error)
Array: Unrecognized type, may only use numbers or lists, found type Array.

Best Answer

The following code works to convert feature collection to arrays

var tableList = table.toList(200).map(function(element) {
  return ee.Feature(element).toArray(data)
})

var matA = ee.Array.cat(tableList, 1)

Related Solutions

Google Earth Engine – Batch Processing Data of Multiple ROIs in Google Earth Engine

Here's an example that hopefully does something like what you want, but you'll need to modify it to meet your requirements for "manually selected marker points" and Sentinel 2.

In general, do NOT use for-loops or getInfo(). To be clear, DO NOT USE FOR LOOPS unless you have a very good reason to be doing so. If you don't know, use map() for all the reasons described here, here, here and here. (And check the same guides for why to NOT use getInfo() or convert to a list as I've done here.) The reason it's OK to do this here (necessary, in fact) is because Export is a client side function and you can't use a client function in map().

// Get some imagery to play with.
var landsat = ee.ImageCollection("LANDSAT/LC08/C01/T1")
    .filterDate('2016-01-01', '2017-01-01');

var composite = ee.Algorithms.Landsat.simpleComposite({
  collection: landsat,
  asFloat: true
});

var rgbVis = {bands: ["B4", "B3", "B2"], min:0, max: 0.3};
Map.addLayer(composite, rgbVis, "RGB");

// This is a hacky way to get a pixel grid at arbitrary resolution.
var pixels = ee.Image.random().multiply(10000000).toInt32()
    .reduceToVectors({
      reducer: ee.Reducer.countEvery(),
      geometry: Map.getBounds(true),
      geometryType: 'bb' ,
      eightConnected: false,
      scale: 20000,
      crs: 'EPSG:4326'
    });
Map.addLayer(pixels);

// Only do this is you have a few regions.  Not suitable for 
// large feature collections.
var pixelsList = pixels.toList(pixels.size());

// This is one of the few places in the EE API where you need 
// a for-loop and a getInfo() call.  Export is a client function.
for (var i=0; i<pixels.size().getInfo(); i++) {
  Export.image.toDrive({
    image: composite, 
    description: 'foo_' + i, 
    fileNamePrefix: 'foo_' + i, 
    region: ee.Feature(pixelsList.get(i)).geometry(), 
    scale: 30, 
  });
}

If you really need precise control over the export regions, you can make lists of coordinates and turn those into a collection of the ROIs you want to export. All that aside, you still need to click 'Run' on the exports. If you want it completely automated, use the Python API and ee.batch.Export followed by task.start().

[GIS] Extracting only some properties of each feature from a feature collection and creating a new a feature collection from them using Google Earth Engine

I think this should work:

var dates = ee.List(["property1", "property2"]);

var new_NDVI=NDVI.map(function(f){
    f = ee.Feature(f);
    return ee.Feature(null, f.toDictionary(dates));
 });

First of all, you have some syntax errors in your example code. You need to give the inputs of the function, here that is "(f)", after the "function" statement. Then you also forgot the curly opening bracket "{".

The documentation for "ee.Feature" says you need to give a geometry first, and then a dictionary with properties for the respective feature. In this case we say the geometry is non-existant, i.e. "null". The dictionary is create by calling the "toDictionary" method on the input feature "f". Dates needs to be a list of property names that exist in the features of the NDVI feature-collection.

Also note that there is no need to call the ".values(dates)" method, because that will turn the dictionary into a list.

Best Answer

Related Solutions

Google Earth Engine – Batch Processing Data of Multiple ROIs in Google Earth Engine

[GIS] Extracting only some properties of each feature from a feature collection and creating a new a feature collection from them using Google Earth Engine

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