The grid (core) · console.warn

statistics.compare: each group needs at leas...

Printed by The grid (core), prefixed [lattice], since 1.106.0.

Warnings reference › compare:small

Identifier: compare:small
Raised by: The grid (core)
Since: 1.106.0

What happened

A group with one or two readings cannot support the test: the variance (or the rank spread) has nothing to estimate, and a p-value from it would be noise. null is returned rather than a result from a sample this small.

The fix

Compare groups with at least three rows each.

Reference

Covered in full at the API reference.