03. Core API Reference

split

split(data, strategy; rng)

Dispatches to strategy._split. Returns (train, test) index vectors.

splitwithpositions

split_with_positions(data, s, core_algorithm; rng=Random.default_rng())

A utility function that handles mapping between user-facing indices (which may be non-1-based or non-contiguous) and internal 1:N positions. The core_algorithm should operate on positions 1:N and return (train_pos, test_pos), which are then mapped back to the correct indices for the user.

SplitStrategy Interface

To add a new strategy, subtype SplitStrategy and implement:

_split(data, s::YourStrategy; rng)

Utility Functions

• sample_indices(data): returns iterable indices of samples (default: 1:size(data,1), but now robust to any AbstractArray axes).
• ValidFraction: bounds-checked fraction type for split ratios.

Example: Custom Splitter (new pattern)

struct MySplit <: SplitStrategy; frac; end

function mysplit(N, s, rng, data)
    cut = floor(Int, s.frac * N)
    train_pos = 1:cut
    test_pos = (cut+1):N
    return train_pos, test_pos
end

function _split(data, s::MySplit; rng=Random.default_rng())
    split_with_positions(data, s, mysplit; rng=rng)
end