sampling - Export pixel neighborhood in Google Earth Engine

I have some points and know how to extract the Landsat data at these points and build and export a training dataset to feed an external classifier. But how can I efficiently and automatically build a small patch of 2-D pixels (say 3x3 neighborhood) around each sample point to build and export a similar training dataset to feed an external convolutional classifier?

Answer

I think what you need is ee.Image.neighborhoodToArray. I give an example:

var i = ee.Image.random().addBands(ee.Image.random(1)).clip(geometry)
Map.addLayer(i)

var neig = i.neighborhoodToArray(ee.Kernel.square(1))

var training = neig.reduceRegions({

  collection:points,
  scale: 1000,
  reducer: 'first'
})

Map.addLayer(training)

link: https://code.earthengine.google.com/a406f32c989923eae10d73af8b1871be