.maybe_prepend_baseline: Prepend a baseline column of 1s to a 3-D stats array
Description
Checks whether the formula includes an intercept (no -1).
If so, prepends a baseline{suffix} slice of 1s along dim 3.
Usage
.maybe_prepend_baseline(arr, formula, suffix)
Value
Updated array with P+1 slices, or the original if no intercept.
Arguments
- arr
3-D array \[M × D × P\] or NULL.
- formula
Formula that produced the array.
- suffix
".start" or ".end".