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Validation

Overview

We provide various geostatistical cross-validation methods to compare interpolation models or learning models. These methods are accessible through the cverror function:

GeoStatsValidation.cverror — Function
cverror(model::GeoStatsModel, geotable, method; kwargs...)

Estimate cross-validation error of geostatistical model on given geotable with error estimation method using Interpolate or InterpolateNeighbors depending on kwargs.

cverror(model::StatsLearnModel, geotable, method)
cverror((model, feats => targs), geotable, method)

Estimate cross-validation error of statistical learning model on given geotable with error estimation method.

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As an example, consider the block cross-validation error of the following decision tree learning model:

using GeoStats
using GeoIO

# load geospatial data
Ω = GeoIO.load("data/agriculture.csv", coords = ("x", "y"))

# 20%/80% split along the (1, -1) direction
Ωₛ, Ωₜ = geosplit(Ω, 0.2, (1.0, -1.0))

# features and label for supervised learning
feats = ["band1", "band2", "band3", "band4"]
label = "crop"

# learning model
model = DecisionTreeClassifier()

# loss function
loss = MisclassLoss()

# block cross-validation with r = 30.
bcv = BlockValidation(30., loss = Dict("crop" => loss))

# estimate of generalization error
ϵ̂ = cverror((model, feats => label), Ωₛ, bcv)
Dict{Symbol, Float64} with 1 entry:
  :crop => 0.232103

We can unhide the labels in the target domain and compute the actual error for comparison:

# train in Ωₛ and predict in Ωₜ
Ω̂ₜ = Ωₜ |> Learn(Ωₛ, model, feats => label)

# actual error of the model
ϵ = mean(loss.(Ωₜ.crop, Ω̂ₜ.crop))
0.23318176518596245

Methods

Leave-one-out

Leave-ball-out

K-fold

Block

Weighted

GeoStatsValidation.WeightedValidation — Type
WeightedValidation(weighting, folding; lambda=1.0, loss=Dict())

An error estimation method which samples are weighted with weighting method and split into folds with folding method. Weights are raised to lambda power in [0,1]. Optionally, specify a dictionary with loss functions from LossFunctions.jl for some of the variables.

References

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Density-ratio

GeoStatsValidation.DensityRatioValidation — Type
DensityRatioValidation(k; [options])

Density ratio validation where weights are first obtained with density ratio estimation, and then used in k-fold weighted cross-validation.

Options

  • shuffle - Shuffle the data before folding (default to true)
  • estimator - Density ratio estimator (default to LSIF())
  • optlib - Optimization library (default to default_optlib(estimator))
  • lambda - Power of density ratios (default to 1.0)
  • loss - Dictionary with loss functions (default to Dict())

Please see DensityRatioEstimation.jl for a list of supported estimators.

References

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