Using the covariance reducer in Earth Engine

Question

How do you apply the covariance reducer to an array in Earth Engine? I have two lists containing values that I have sampled from an image and would like to calculate their covariance matrix. My attempt is

a1 = ee.Array([1,2,3,4,5]) 
a2 = ee.Array([5,4,3,2,1])
cov = ee.Array.cat([a1, a2], 1).tranpose() \
  .reduce(reducer = ee.Reducer.covariance(), axes = [0])

which would return

Array.reduce: Type must be a 1D EEArray.

Answer 1

The covariance reducer works on lists of 1D Arrays. So this code should work:

var a1 = ee.Array([1,2,3,4,5]) 
var a2 = ee.Array([5,4,3,2,1])
var cov = ee.List([a1, a2])
  .reduce(ee.Reducer.covariance())
print(cov)