GEE: Export an Array into a Table

Question

I have created an array with the results of a Pearson correlation between image bands. I want to convert that array into a properly structured Table. Currently, I am able to export it, but the output table looks like this:

All the lists in the array appear in the same cell. Instead, I would like to have each list in a row, and each element in the list in a column. Even better if I could add the name of the columns (band1, band2, R, p-value)

My code: https://code.earthengine.google.com/?scriptPath=users%2Fericacinerea%2Fgee_training%3Aband_correlation

and one extract of it:

//check the correlation between bands in a stack

//var list_of_results = ee.List([]);
var myArray = []; // recommended way

//Get the names of the input bands
var bands = ["b1","b2","b3","b4"];

for (var i=0; i<bands.length;i++) {
  for (var j=i+1; j<bands.length;j++) {
    var sample = image.sample({'region':aoi, 
                            'scale': 1000, 
                            'projection': 'EPSG:4326',
                            'numPixels':100});
    var correl = ee.Reducer.pearsonsCorrelation();
    var reduced = sample.reduceColumns(correl, [bands[i], bands[j]]);
    var results = [bands[i],bands[j], reduced.get('correlation'), reduced.get('p-value')];
    //print(results);
    myArray.push(results);
    //var list_of_results = list_of_results.add(results);
  }
}

//print outputs in lines
var csv = myArray.map(function(row){ 
  //var list = [row[0], row[1], row[2], row[3]];
  print(ee.String(row[0]).cat(',').cat(row[1]).cat(',').cat(row[2]).cat(',').cat(row[3]));
});

Export.table.toDrive(
    ee.FeatureCollection([
        ee.Feature(null, {myArray: myArray})
    ]));

Answer 1

Based in printed myArray variable in GEE console, you have a list of 6 elements with 4 elements in each one (total 24 possibilities). For reducing to only 12 possibilities (including band1, band2, R, p-value as column name), my suggestion is to modify your script as follows:

print(myArray);

//print outputs in lines
var csv = myArray.map(function(row){ 
  //var list = [row[0], row[1], row[2], row[3]];
  //print(ee.String(row[0]).cat(',').cat(row[1]).cat(',').cat(row[2]).cat(',').cat(row[3]));
});

Export.table.toDrive(
    ee.FeatureCollection([
        ee.Feature(null, {
          'b1,2_R': ee.List(ee.List(myArray).get(0)).get(2),
          'b1,2_p_value': ee.List(ee.List(myArray).get(0)).get(3),
          'b1,3_R': ee.List(ee.List(myArray).get(1)).get(2),
          'b1,3_p_value': ee.List(ee.List(myArray).get(1)).get(3),
          'b1,4_R': ee.List(ee.List(myArray).get(2)).get(2),
          'b1,4_p_value': ee.List(ee.List(myArray).get(2)).get(3),
          'b2,3_R': ee.List(ee.List(myArray).get(3)).get(2),
          'b2,3_p_value': ee.List(ee.List(myArray).get(3)).get(3),
          'b2,4_R': ee.List(ee.List(myArray).get(4)).get(2),
          'b2,4_p_value': ee.List(ee.List(myArray).get(4)).get(3),
          'b3,4_R': ee.List(ee.List(myArray).get(5)).get(2),
          'b3,4_p_value': ee.List(ee.List(myArray).get(5)).get(3)

        })
    ]));

Above modifications it will produce each list in a row and each element in the list in a column as you desire. It can be observed in following image for new exported CSV file. Complete code here.

Answer 2

I have finally solved the problem, see the new code at: https://code.earthengine.google.com/?scriptPath=users%2Fericacinerea%2Fgee_training%3Aband_correlation_v2

//check the correlation between bands in a stack

var myArray = []; // recommended way

//Get the names of the input bands
var bands = ["b1","b2","b3","b4"];

for (var i=0; i<bands.length;i++) {
  for (var j=i+1; j<bands.length;j++) {
    var sample = image.sample({'region':aoi, 
                            'scale': 1000, 
                            'projection': 'EPSG:4326',
                            'numPixels':100});
    var correl = ee.Reducer.pearsonsCorrelation();
    var reduced = sample.reduceColumns(correl, [bands[i], bands[j]]);
    var results = {'band1':bands[i],'band2': bands[j], 'R': reduced.get('correlation'), 'p-value': reduced.get('p-value')};
    //print(results);
    myArray.push(results);
    //var list_of_results = list_of_results.add(results);
  }
}

var band_correlation_results = ee.FeatureCollection(myArray
  .map(function (dict, i) {
    return ee.Feature(null, dict);
  })
);

print(band_correlation_results, 'band_correlation_results');


Export.table.toDrive(band_correlation_results);

And the output looks like this: