Machines

fitted_params(mach)

Return the learned parameters for a machine mach that has been fit!, for example the coefficients in a linear model.

This is a named tuple and human-readable if possible.

If mach is a machine for a composite model, such as a model constructed using @pipeline, then the returned named tuple has the composite type's field names as keys. The corresponding value is the fitted parameters for the machine in the underlying learning network bound to that model. (If multiple machines share the same model, then the value is a vector.)

using MLJ
@load LogisticClassifier pkg=MLJLinearModels
X, y = @load_crabs;
pipe = @pipeline Standardizer LogisticClassifier
mach = machine(pipe, X, y) |> fit!

julia> fitted_params(mach).logistic_classifier
(classes = CategoricalArrays.CategoricalValue{String,UInt32}["B", "O"],
 coefs = Pair{Symbol,Float64}[:FL => 3.7095037897680405, :RW => 0.1135739140854546, :CL => -1.6036892745322038, :CW => -4.415667573486482, :BD => 3.238476051092471],
 intercept = 0.0883301599726305,)

Additional keys, machines and fitted_params_given_machine, give a list of all machines in the underlying network, and a dictionary of fitted parameters keyed on those machines.

```

report(mach)

Return the report for a machine mach that has been fit!, for example the coefficients in a linear model.

This is a named tuple and human-readable if possible.

If mach is a machine for a composite model, such as a model constructed using @pipeline, then the returned named tuple has the composite type's field names as keys. The corresponding value is the report for the machine in the underlying learning network bound to that model. (If multiple machines share the same model, then the value is a vector.)

using MLJ
@load LinearBinaryClassifier pkg=GLM
X, y = @load_crabs;
pipe = @pipeline Standardizer LinearBinaryClassifier
mach = machine(pipe, X, y) |> fit!

julia> report(mach).linear_binary_classifier
(deviance = 3.8893386087844543e-7,
 dof_residual = 195.0,
 stderror = [18954.83496713119, 6502.845740757159, 48484.240246060406, 34971.131004997274, 20654.82322484894, 2111.1294584763386],
 vcov = [3.592857686311793e8 9.122732393971942e6 … -8.454645589364915e7 5.38856837634321e6; 9.122732393971942e6 4.228700272808351e7 … -4.978433790526467e7 -8.442545425533723e6; … ; -8.454645589364915e7 -4.978433790526467e7 … 4.2662172244975924e8 2.1799125705781363e7; 5.38856837634321e6 -8.442545425533723e6 … 2.1799125705781363e7 4.456867590446599e6],)

Additional keys, machines and report_given_machine, give a list of all machines in the underlying network, and a dictionary of reports keyed on those machines.

```

machine(model, args...)

Construct a Machine object binding a model, storing hyper-parameters of some machine learning algorithm, to some data, args. When building a learning network, Node objects can be substituted for concrete data.

machine(Xs; oper1=node1, oper2=node2, ...)
machine(Xs, ys; oper1=node1, oper2=node2, ...)
machine(Xs, ys, ws; oper1=node1, oper2=node2, ...)

Construct a special machine called a learning network machine, that "wraps" a learning network, usually in preparation to export the network as a stand-alone composite model type. The keyword arguments declare what nodes are called when operations, such as predict and transform, are called on the machine.

In addition to the operations named in the constructor, the methods fit!, report, and fitted_params can be applied as usual to the machine constructed.

machine(Probablistic(), args...; kwargs...)
machine(Deterministic(), args...; kwargs...)
machine(Unsupervised(), args...; kwargs...)
machine(Static(), args...; kwargs...)

Same as above, but specifying explicitly the kind of model the learning network is to meant to represent.

Learning network machines are not to be confused with an ordinary machine that happens to be bound to a stand-alone composite model (i.e., an exported learning network).

Examples

Supposing a supervised learning network's final predictions are obtained by calling a node yhat, then the code

mach = machine(Deterministic(), Xs, ys; predict=yhat)
fit!(mach; rows=train)
predictions = predict(mach, Xnew) # `Xnew` concrete data

is equivalent to

fit!(yhat, rows=train)
predictions = yhat(Xnew)

Here Xs and ys are the source nodes receiving, respectively, the input and target data.

In a unsupervised learning network for clustering, with single source node Xs for inputs, and in which the node Xout delivers the output of dimension reduction, and yhat the class labels, one can write

mach = machine(Unsupervised(), Xs; transform=Xout, predict=yhat)
fit!(mach)
transformed = transform(mach, Xnew) # `Xnew` concrete data
predictions = predict(mach, Xnew)

which is equivalent to

fit!(Xout)
fit!(yhat)
transformed = Xout(Xnew)
predictions = yhat(Xnew)

MLJBase.fit_only!(mach::Machine; rows=nothing, verbosity=1, force=false)

Without mutating any other machine on which it may depend, perform one of the following actions to the machine mach, using the data and model bound to it, and restricting the data to rows if specified:

• Ab initio training. Ignoring any previous learned parameters and cache, compute and store new learned parameters. Increment mach.state.

• Training update. Making use of previous learned parameters and/or cache, replace or mutate existing learned parameters. The effect is the same (or nearly the same) as in ab initio training, but may be faster or use less memory, assuming the model supports an update option (implements MLJBase.update). Increment mach.state.

• No-operation. Leave existing learned parameters untouched. Do not increment mach.state.

Training action logic

For the action to be a no-operation, either mach.frozen == true or none of the following apply:

• (i) mach has never been trained (mach.state == 0).

• (ii) force == true

• (iii) The state of some other machine on which mach depends has changed since the last time mach was trained (ie, the last time mach.state was last incremented)

• (iv) The specified rows have changed since the last retraining.

• (v) mach.model has changed since the last retraining.

In cases (i) - (iv), mach is trained ab initio. In case (v) a training update is applied.

To freeze or unfreeze mach, use freeze!(mach) or thaw!(mach).

Implementation detail

The data to which a machine is bound is stored in mach.args. Each element of args is either a Node object, or, in the case that concrete data was bound to the machine, it is concrete data wrapped in a Source node. In all cases, to obtain concrete data for actual training, each argument N is called, as in N() or N(rows=rows), and either MLJBase.fit (ab initio training) or MLJBase.update (training update) is dispatched on mach.model and this data. See the "Adding models for general use" section of the MLJ documentation for more on these lower-level training methods.

MLJ.save(filename, mach::Machine; kwargs...)
MLJ.save(io, mach::Machine; kwargs...)

MLJBase.save(filename, mach::Machine; kwargs...)
MLJBase.save(io, mach::Machine; kwargs...)

Serialize the machine mach to a file with path filename, or to an input/output stream io (at least IOBuffer instances are supported).

The format is JLSO (a wrapper for julia native or BSON serialization) unless a custom format has been implemented for the model type of mach.model. The keyword arguments kwargs are passed to the format-specific serializer, which in the JSLO case include these:

See (see https://github.com/invenia/JLSO.jl for details.

Machines are de-serialized using the machine constructor as shown in the example below. Data (or nodes) may be optionally passed to the constructor for retraining on new data using the saved model.

Example

using MLJ
tree = @load DecisionTreeClassifier
X, y = @load_iris
mach = fit!(machine(tree, X, y))

MLJ.save("tree.jlso", mach, compression=:none)
mach_predict_only = machine("tree.jlso")
predict(mach_predict_only, X)

mach2 = machine("tree.jlso", selectrows(X, 1:100), y[1:100])
predict(mach2, X) # same as above

fit!(mach2) # saved learned parameters are over-written
predict(mach2, X) # not same as above

# using a buffer:
io = IOBuffer()
MLJ.save(io, mach)
seekstart(io)
predict_only_mach = machine(io)
predict(predict_only_mach, X)