Computing a pixel-wise R-squared value between two image collections - collections

Question

I have several image collections: september_CCI (chlorophyll-carotenoid index), SDD (snow disappearance date), cumulative_summer_VPD (vapor pressure deficit), and cumulative_summer_precipitation. Each image collection covers the same years (2000-2020) and they are the same spatial dimensions.
CCI is the dependent variable. SDD, cumulative_summer_VPD, and cumulative_summer_precipitation are the independent variables.
I would like to compute the pixel-wise R-squared between CCI and each of the independent variables.
Here's some code that I found elsewhere and have tried to adapt to my case:
// 1. Join datasets. First, define filter. This is based on the date.
var filter = ee.Filter.equals({
leftField: 'system:time_start',
rightField: 'system:time_start'
});
// 2. Create the join.
var innerJoin = ee.Join.inner('primary', 'secondary');
// 3. Apply the join.
var merge = innerJoin.apply(septCCI, sdd2, filter);
// 4. Merge both collections.
var mergedCCI_SDD = merge.map(function(f){
var cci = ee.Image(f.get('primary')).rename('cci');
var sdd = ee.Image(f.get('secondary')).rename('sdd');
return cci.addBands(sdd).copyProperties(cci);
});
var covariance = function(mergedCCI_SDD, cci, sdd) {
return mergedCCI_SDD.select([cci, sdd]).map(function(image) {
return image.toArray();
}).reduce(ee.Reducer.covariance(), 8);
};
var correlation = function(vcArrayImage) {
var covariance = ee.Image(vcArrayImage).arrayGet([0, 1]);
var sd0 = ee.Image(vcArrayImage).arrayGet([0, 0]).sqrt();
var sd1 = ee.Image(vcArrayImage).arrayGet([1, 1]).sqrt();
return covariance.divide(sd0).divide(sd1).rename('correlation');
};
// Compute and display cross-covariance.
var covCCI_SDD = covariance(mergedCCI_SDD, 'cci', 'sdd');
Map.addLayer(covCCI_SDD.arrayGet([0, 1]), {}, 'CCI-SDD cov');
// Compute and display cross-correlation.
var corrCCI_SDD = correlation(covCCI_SDD);
Map.addLayer(corrCCI_SDD, {min: -0.5, max: 0.5}, 'CCI-SDD corr');
When I try to run this (within a much larger piece of code), I get the following error, which corresponds to the line on which
there is this code: return image.toArray();
Line 643: Required argument (properties) missing to function: Feature.toArray(feature, properties)
Creates an array from the given properties of an object, which must all be numbers.
Args:
feature (Feature): The object from which to select array properties.
properties (List): The property selectors for each array element.
Thanks for any help you can provide.