name: type-u4
kind: type
description: 4-bit unsigned integer; bit-packed with adjacent u4 / packed_bool fields.
type: reference
applies_to: inspect, predict
Bytes
ByteSize() == 0 — bit-packed. Each value is 4 bits; two u4 fields share one byte (high nibble + low nibble). Stride math handled by Schema.RecordByteSize; place packed runs together for optimal layout. FieldType.IsBitPacked() reports true.
Range
0..15 (4-bit unsigned). Natural fit for small ordinals — Likert 1..5, letter grades, satisfaction tiers, or any closed cardinal scale that lives below 16 distinct values.
Null
Orthogonal to type. Mark the field Nullable: true and the per-record null bitmap carries the actual null state. No inline sentinel — 0 is the integer zero, not null. IsNumericForAnalytics() is true, so null-skip aggregator semantics apply.
Dictionary
Absent. u4 carries no inline dictionary block; values are interpreted as plain unsigned integers. If you need labeled categories, prefer categorical_u8 (with ≤256 dict entries).
See
- Skill:
cohort-schema-design(Field-type matrix, Bit-packed runs). - Cross-link:
aggregation-designfor analytics-numeric coverage.