JuliaAI · ablaom · Feb 19, 2025 · Feb 20, 2025 · Feb 20, 2025 · Feb 20, 2025
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
@@ -29,7 +29,7 @@ jobs:
         with:
           version: ${{ matrix.version }}
           arch: ${{ matrix.arch }}
-      - uses: actions/cache@v1
+      - uses: julia-actions/cache@v1
         env:
           cache-name: cache-artifacts
         with:

diff --git a/Project.toml b/Project.toml
@@ -1,7 +1,7 @@
 name = "LearnAPI"
 uuid = "92ad9a40-7767-427a-9ee6-6e577f1266cb"
 authors = ["Anthony D. Blaom <[email protected]>"]
-version = "1.0.1"
+version = "2.0.0"
 
 [compat]
 julia = "1.10"

diff --git a/README.md b/README.md
@@ -24,7 +24,7 @@ Here `learner` specifies the configuration the algorithm (the hyperparameters) w
 `model` stores learned parameters and any byproducts of algorithm execution.
 
 LearnAPI.jl is mostly method stubs and lots of documentation. It does not provide
-meta-algorithms, such as cross-validation or hyperparameter optimization, but does aim to
+meta-algorithms, such as cross-validation, hyperparameter optimization, or model composition, but does aim to
 support such algorithms.
 
 ## Related packages
@@ -37,6 +37,8 @@ support such algorithms.
 
 - [StatisticalMeasures.jl](https://github.com/JuliaAI/StatisticalMeasures.jl): Package providing metrics, compatible with LearnAPI.jl
 
+- [StatsModels.jl](https://github.com/JuliaStats/StatsModels.jl): Provides the R-style formula implementation of data preprocessing handled by [LearnDataFrontEnds.jl](https://github.com/JuliaAI/LearnDataFrontEnds.jl)
+
 ### Selected packages providing alternative API's
 
 The following alphabetical list of packages provide public base API's.  Some provide

diff --git a/ROADMAP.md b/ROADMAP.md
@@ -14,7 +14,7 @@
   "Common Implementation Patterns". As real-world implementations roll out, we could
   increasingly point to those instead, to conserve effort
   - [x] regression
-  - [ ] classification
+  - [x] classification
   - [ ] clustering
   - [x] gradient descent
   - [x] iterative algorithms

diff --git a/docs/Project.toml b/docs/Project.toml
@@ -2,7 +2,6 @@
 Documenter = "e30172f5-a6a5-5a46-863b-614d45cd2de4"
 DocumenterInterLinks = "d12716ef-a0f6-4df4-a9f1-a5a34e75c656"
 LearnAPI = "92ad9a40-7767-427a-9ee6-6e577f1266cb"
-LearnTestAPI = "3111ed91-c4f2-40e7-bb19-7f6c618409b8"
 MLCore = "c2834f40-e789-41da-a90e-33b280584a8c"
 ScientificTypesBase = "30f210dd-8aff-4c5f-94ba-8e64358c1161"
 Tables = "bd369af6-aec1-5ad0-b16a-f7cc5008161c"

diff --git a/docs/make.jl b/docs/make.jl
@@ -2,12 +2,12 @@ using Documenter
 using LearnAPI
 using ScientificTypesBase
 using DocumenterInterLinks
-using LearnTestAPI
+# using LearnTestAPI
 
 const  REPO = Remotes.GitHub("JuliaAI", "LearnAPI.jl")
 
 makedocs(
-    modules=[LearnAPI, LearnTestAPI],
+    modules=[LearnAPI, ], #LearnTestAPI],
     format=Documenter.HTML(
         prettyurls = true,#get(ENV, "CI", nothing) == "true",
         collapselevel = 1,
@@ -18,6 +18,7 @@ makedocs(
         "Reference" => [
             "Overview" => "reference.md",
             "Public Names" => "list_of_public_names.md",
+            "Kinds of learner" => "kinds_of_learner.md",
             "fit/update" => "fit_update.md",
             "predict/transform" => "predict_transform.md",
             "Kinds of Target Proxy" => "kinds_of_target_proxy.md",

diff --git a/docs/src/anatomy_of_an_implementation.md b/docs/src/anatomy_of_an_implementation.md
@@ -1,6 +1,7 @@
 # Anatomy of an Implementation
 
-The core LearnAPI.jl pattern looks like this:
+LearnAPI.jl supports three core patterns. The default pattern, known as the
+[`LearnAPI.Descriminative`](@ref) pattern, looks like this:
 
 ```julia
 model = fit(learner, data)
@@ -10,38 +11,51 @@ predict(model, newdata)
 Here `learner` specifies [hyperparameters](@ref hyperparameters), while `model` stores
 learned parameters and any byproducts of algorithm execution.
 
-Variations on this pattern:
+[Transformers](@ref) ordinarily implement `transform` instead of `predict`. For more on
+`predict` versus `transform`, see [Predict or transform?](@ref)
 
-- [Transformers](@ref) ordinarily implement `transform` instead of `predict`. For more on
-  `predict` versus `transform`, see [Predict or transform?](@ref)
+Two other `fit`/`predict`/`transform` patterns supported by LearnAPI.jl are:
+[`LearnAPI.Generative`](@ref) which has the form:
 
-- ["Static" (non-generalizing) algorithms](@ref static_algorithms), which includes some
-  simple transformers and some clustering algorithms, have a `fit` that consumes no
-  `data`. Instead `predict` or `transform` does the heavy lifting.
+```julia
+model = fit(learner, data)
+predict(model) # a single distribution, for example
+```
 
-- In [density estimation](@ref density_estimation), the `newdata` argument in `predict` is
-  missing.
+and [`LearnAPI.Static`](@ref), which looks like this:
+
+```julia
+model = fit(learner) # no `data` argument
+predict(model, data) # may mutate `model` to record byproducts of computation
+```
 
-These are the basic possibilities.
+Do not read too much into the names for these patterns, which are formalized [here](@ref kinds_of_learner). Use may not always correspond to prior associations.
 
-Elaborating on the core pattern above, this tutorial details an implementation of the
-LearnAPI.jl for naive [ridge regression](https://en.wikipedia.org/wiki/Ridge_regression)
-with no intercept. The kind of workflow we want to enable has been previewed in [Sample
-workflow](@ref). Readers can also refer to the [demonstration](@ref workflow) of the
-implementation given later.
+Elaborating on the common `Descriminative` pattern above, this tutorial details an
+implementation of the LearnAPI.jl for naive [ridge
+regression](https://en.wikipedia.org/wiki/Ridge_regression) with no intercept. The kind of
+workflow we want to enable has been previewed in [Sample workflow](@ref). Readers can also
+refer to the [demonstration](@ref workflow) of the implementation given later.
 
-## A basic implementation
+!!! tip "Quick Start for new implementations"
 
-See [here](@ref code) for code without explanations.
+	1. From this tutorial, read at least "[A basic implementation](@ref)" below.
+	1. Looking over the examples in "[Common Implementation Patterns](@ref patterns)", identify the appropriate core learner pattern above for your algorithm.
+	1. Implement `fit` (probably following an existing example). Read the [`fit`](@ref) document string to see what else may need to be implemented, paying particular attention to the "New implementations" section.
+	3. Rinse and repeat with each new method implemented.
+	4. Identify any additional [learner traits](@ref traits) that have appropriate overloadings; use the [`@trait`](@ref) macro to define these in one block.
+	5. Ensure your implementation includes the compulsory method [`LearnAPI.learner`](@ref) and compulsory traits [`LearnAPI.constructor`](@ref) and [`LearnAPI.functions`](@ref). Read and apply "[Testing your implementation](@ref)".
 
-We suppose our algorithm's `fit` method consumes data in the form `(X, y)`, where
-`X` is a suitable table¹ (the features) and `y` a vector (the target).
+	If you get stuck, refer back to this tutorial and the [Reference](@ref reference) sections.
 
-!!! important
 
-    Implementations wishing to support other data
-    patterns may need to take additional steps explained under
-    [Other data patterns](@ref di) below.
+## A basic implementation
+
+See [here](@ref code) for code without explanations.
+
+Let us suppose our algorithm's `fit` method is to consume data in the form `(X, y)`, where
+`X` is a suitable table¹ (the features, a.k.a., covariates or predictors) and `y` a vector
+(the target, a.k.a., labels or response).
 
 The first line below imports the lightweight package LearnAPI.jl whose methods we will be
 extending. The second imports libraries needed for the core algorithm.
@@ -158,6 +172,22 @@ If the kind of proxy is omitted, as in `predict(model, Xnew)`, then a fallback g
 first element of the tuple returned by [`LearnAPI.kinds_of_proxy(learner)`](@ref), which
 we overload appropriately below.
 
+### Data deconstructors: `target` and `features`
+
+LearnAPI.jl is flexible about the form of training `data`. However, to buy into
+meta-functionality, such as cross-validation, we'll need to say something about the
+structure of this data. We implement [`LearnAPI.target`](@ref) to say what
+part of the data constitutes a [target variable](@ref proxy), and
+[`LearnAPI.features`](@ref) to say what are the features (valid `newdata` in a
+`predict(model, newdata)` call):
+
+```@example anatomy
+LearnAPI.target(learner::Ridge, (X, y)) = y
+LearnAPI.features(learner::Ridge, (X, y)) = X
+```
+
+Another data deconstructor, for learners that support per-observation weights in training,
+is [`LearnAPI.weights`](@ref).
 
 ### [Accessor functions](@id af)
 
@@ -241,15 +271,11 @@ the *type* of the argument.
 ### The `functions` trait
 
 The last trait, `functions`, above returns a list of all LearnAPI.jl methods that can be
-meaningfully applied to the learner or associated model, with the exception of traits. You
-always include the first five you see here: `fit`, `learner`, `clone` ,`strip`,
-`obs`. Here [`clone`](@ref) is a utility function provided by LearnAPI that you never
-overload, while [`obs`](@ref) is discussed under [Providing a separate data front
-end](@ref) below and is always included because it has a meaningful fallback. The
-`features` method, here provided by a fallback, articulates how the features `X` can be
-extracted from the training data `(X, y)`. We must also include `target` here to flag our
-model as supervised; again the method itself is provided by a fallback valid in the
-present case.
+meaningfully applied to the learner or the output of `fit` (denoted `model` above), with
+the exception of traits. You always include the first five you see here: `fit`, `learner`,
+`clone` ,`strip`, `obs`. Here [`clone`](@ref) is a utility function provided by LearnAPI
+that you never overload, while [`obs`](@ref) is discussed under [Providing a separate data
+front end](@ref) below and is always included because it has a meaningful fallback.
 
 See [`LearnAPI.functions`](@ref) for a checklist of what the `functions` trait needs to
 return.
@@ -340,11 +366,6 @@ assumptions about data from those made above.
   under [Providing a separate data front end](@ref) below; or (ii) overload the trait
   [`LearnAPI.data_interface`](@ref) to specify a more relaxed data API.
 
-- Where the form of data consumed by `fit` is different from that consumed by
-  `predict/transform` (as in classical supervised learning) it may be necessary to
-  explicitly overload the functions [`LearnAPI.features`](@ref) and (if supervised)
-  [`LearnAPI.target`](@ref). The same holds if overloading [`obs`](@ref); see below.
-
 
 ## Providing a separate data front end
 
@@ -414,7 +435,7 @@ The [`obs`](@ref) methods exist to:
 
 !!! important
 
-    While many new learner implementations will want to adopt a canned data front end, such as those provided by [LearnDataFrontEnds.jl](https://juliaai.github.io/LearnAPI.jl/dev/), we
+    While many new learner implementations will want to adopt a canned data front end, such as those provided by [LearnDataFrontEnds.jl](https://juliaai.github.io/LearnDataFrontEnds.jl/dev/), we
     focus here on a self-contained implementation of `obs` for the ridge example above, to show
     how it works.
 
@@ -448,14 +469,14 @@ newobservations = MLCore.getobs(observations, test_indices)
 predict(model, newobservations)
 ```
 
-which works for any non-static learner implementing `predict`, no matter how one is
-supposed to accesses the individual observations of `data` or `newdata`. See also the
-demonstration [below](@ref advanced_demo). Furthermore, fallbacks ensure the above pattern
-still works if we choose not to implement a front end at all, which is allowed, if
-supported `data` and `newdata` already implement `getobs`/`numobs`.
+which works for any [`LearnAPI.Descriminative`](@ref) learner implementing `predict`, no
+matter how one is supposed to accesses the individual observations of `data` or
+`newdata`. See also the demonstration [below](@ref advanced_demo). Furthermore, fallbacks
+ensure the above pattern still works if we choose not to implement a front end at all,
+which is allowed, if supported `data` and `newdata` already implement `getobs`/`numobs`.
 
-Here we specifically wrap all the preprocessed data into single object, for which we
-introduce a new type:
+In the ridge regression example we specifically wrap all the preprocessed data into single
+object, for which we introduce a new type:
 
 ```@example anatomy2
 struct RidgeFitObs{T,M<:AbstractMatrix{T}}
@@ -476,8 +497,8 @@ function LearnAPI.obs(::Ridge, data)
 end
 ```
 
-We informally refer to the output of `obs` as "observations" (see [The `obs`
-contract](@ref) below). The previous core `fit` signature is now replaced with two
+We informally refer to the output of `obs` as "observations" (see "[The `obs`
+contract](@ref)" below). The previous core `fit` signature is now replaced with two
 methods - one to handle "regular" input, and one to handle the pre-processed data
 (observations) which appears first below:
 
@@ -545,13 +566,10 @@ LearnAPI.predict(model::RidgeFitted, ::Point, Xnew) =
     predict(model, Point(), obs(model, Xnew))
 ```
 
-### `features` and `target` methods
+### Data deconstructors: `features` and `target`
 
-Two methods [`LearnAPI.features`](@ref) and [`LearnAPI.target`](@ref) articulate how
-features and target can be extracted from `data` consumed by LearnAPI.jl
-methods. Fallbacks provided by LearnAPI.jl sufficed in our basic implementation
-above. Here we must explicitly overload them, so that they also handle the output of
-`obs(learner, data)`:
+These methods must be able to handle any `data` supported by `fit`, which includes the
+output of `obs(learner, data)`:
 
 ```@example anatomy2
 LearnAPI.features(::Ridge, observations::RidgeFitObs) = observations.A
@@ -573,7 +591,7 @@ LearnAPI.target(learner::Ridge, data) = LearnAPI.target(learner, obs(learner, da
 
 Since LearnAPI.jl provides fallbacks for `obs` that simply return the unadulterated data
 argument, overloading `obs` is optional. This is provided data in publicized
-`fit`/`predict` signatures already consists only of objects implement the
+`fit`/`predict` signatures already consists only of objects implementing the
 [`LearnAPI.RandomAccess`](@ref) interface (most tables¹, arrays³, and tuples thereof).
 
 To opt out of supporting the MLCore.jl interface altogether, an implementation must

diff --git a/docs/src/common_implementation_patterns.md b/docs/src/common_implementation_patterns.md
@@ -9,8 +9,10 @@ This guide is intended to be consulted after reading [Anatomy of an Implementati
 which introduces the main interface objects and terminology.
 
 Although an implementation is defined purely by the methods and traits it implements, many
-implementations fall into one (or more) of the following informally understood patterns or
-tasks:
+implementations fall into one (or more) of the informally understood patterns or tasks
+below. While some generally fall into one of the core `Descriminative`, `Generative` or
+`Static` patterns detailed [here](@id kinds of learner), there are exceptions (such as
+clustering, which has both `Descriminative` and `Static` variations).
 
 - [Regression](@ref): Supervised learners for continuous targets
 

diff --git a/docs/src/examples.md b/docs/src/examples.md
@@ -24,7 +24,6 @@ end
 Instantiate a ridge regression learner, with regularization of `lambda`.
 """
 Ridge(; lambda=0.1) = Ridge(lambda)
-LearnAPI.constructor(::Ridge) = Ridge
 
 # struct for output of `fit`
 struct RidgeFitted{T,F}
@@ -58,6 +57,10 @@ end
 LearnAPI.predict(model::RidgeFitted, ::Point, Xnew) =
     Tables.matrix(Xnew)*model.coefficients
 
+# data deconstructors:
+LearnAPI.target(learner::Ridge, (X, y)) = y
+LearnAPI.features(learner::Ridge, (X, y)) = X
+
 # accessor functions:
 LearnAPI.learner(model::RidgeFitted) = model.learner
 LearnAPI.coefficients(model::RidgeFitted) = model.named_coefficients
@@ -160,7 +163,7 @@ LearnAPI.predict(model::RidgeFitted, ::Point, observations::AbstractMatrix) =
 LearnAPI.predict(model::RidgeFitted, ::Point, Xnew) =
     predict(model, Point(), obs(model, Xnew))
 
-# methods to deconstruct training data:
+# training data deconstructors:
 LearnAPI.features(::Ridge, observations::RidgeFitObs) = observations.A
 LearnAPI.target(::Ridge, observations::RidgeFitObs) = observations.y
 LearnAPI.features(learner::Ridge, data) = LearnAPI.features(learner, obs(learner, data))

diff --git a/docs/src/features_target_weights.md b/docs/src/features_target_weights.md
@@ -4,7 +4,7 @@ Methods for extracting certain parts of `data` for all supported calls of the fo
 [`fit(learner, data)`](@ref).
 
 ```julia
-LearnAPI.features(learner, data) -> <training "features", suitable input for `predict` or `transform`>
+LearnAPI.features(learner, data) -> <training "features"; suitable input for `predict` or `transform`>
 LearnAPI.target(learner, data) -> <target variable>
 LearnAPI.weights(learner, data) -> <per-observation weights>
 ```
@@ -29,11 +29,11 @@ training_loss = sum(ŷ .!= y)
 
 # Implementation guide
 
-| method                                     | fallback return value                         | compulsory?              |
-|:-------------------------------------------|:---------------------------------------------:|--------------------------|
-| [`LearnAPI.features(learner, data)`](@ref) | `first(data)` if `data` is tuple, else `data` | if fallback insufficient |
-| [`LearnAPI.target(learner, data)`](@ref)   | `last(data)`                                  | if fallback insufficient |
-| [`LearnAPI.weights(learner, data)`](@ref)  | `nothing`                                     | no                       |
+| method                                     | fallback return value | compulsory? |
+|:-------------------------------------------|:---------------------:|-------------|
+| [`LearnAPI.features(learner, data)`](@ref) | no fallback           | no          |
+| [`LearnAPI.target(learner, data)`](@ref)   | no fallback           | no          |
+| [`LearnAPI.weights(learner, data)`](@ref)  | no fallback           | no          |
 
 
 # Reference