pub fn pad_to(v: &[f64], len: usize) -> Vec<f64>Expand description
Right-pad a vector with its last value, or 0.0 when empty.
pad_to is a grow-only helper used to lift a short column up to the common
wire width of a ragged reference frame; the padded tail is never read by a
correctly-sliced reference body. Asking it to shrink a column (target
shorter than the source) is always a caller bug — it would silently drop the
tail of real data — so this is a hard error with an actionable message rather
than a quiet truncation. The usual culprit is padding a full-data column to a
train-split width: pad every column to a single n = max(len) and slice each
by its own semantic length inside the reference body instead.