block19.cs

// step 4: one-hot encode the longitude
var pipeline3 = pipeline2.Append(context.Transforms.Categorical.OneHotEncoding(
        inputColumnName: "BinnedLongitude",
        outputColumnName: "EncodedLongitude"
    ))

    // step 5: one-hot encode the latitude
    .Append(context.Transforms.Categorical.OneHotEncoding(
        inputColumnName: "BinnedLatitude",
        outputColumnName: "EncodedLatitude"
    ))
    
    // step 6: cross the two one-hot encoded columns
    .Append(context.Transforms.CustomMapping<FromLocation, ToLocation>(
        (input, output) => { 
            output.Location = new float[input.EncodedLongitude.Length * input.EncodedLatitude.Length];
            var index = 0;
            for (var i = 0; i < input.EncodedLongitude.Length; i++)
                for (var j = 0; j < input.EncodedLatitude.Length; j++)
                    output.Location[index++] = input.EncodedLongitude[i] * input.EncodedLatitude[j];
        },
        contractName: "Location"
    ))

    // step 7: remove all the columns we don't need anymore
    .Append(context.Transforms.DropColumns(
        "MedianHouseValue",
        "Longitude",
        "Latitude",
        "BinnedLongitude",
        "BinnedLatitude",
        "EncodedLongitude",
        "EncodedLatitude"
    ));