EventFrame - EncodeBox

An EventFrame is a lazy list of clinical events. Chain verbs; nothing hits the database until .to_df().

index = (
    db.diagnosis
    .matching("E11", code_type="10", match="starts_with")
    .occurring(at_least=2, gap_days=30)
    .with_index_date()
    .first_per_patient()
)

Verbs

Verb	Meaning
`matching(codes, code_type=…, match=…)`	Filter by code / type / match mode
`in_position("primary")`	Primary / secondary diagnosis
`occurring(at_least=…, at_most=…, gap_days=…)`	Patient-level occurrence + consecutive gaps
`with_index_date()`	Add `index_date`
`first_per_patient()` / `last_per_patient()`	One row per patient
`between(...)` / `in_years(...)`	Calendar filters
`with_age(...)` / `with_followup(...)`	Attach derived columns
`union(other)`	Stack event streams
`label("name")`	Name a step for repr / attrition
`to_sql()` / `to_df()` / `explain()`	Inspect / run

Match aliases

starts_with / start with, exactly / exactly match, contain, end with.

Gap semantics

gap_days uses consecutive distinct-date gaps (lead()), not span. See Which API?.

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