The dead-column report: every column on a source or transform table from which no chain of edges reaches a target table. In a multi-model lineage that surfaces base-table columns nothing reads and intermediate-model outputs no downstream model consumes, both safe to drop as far as the graph can see.
Arguments
- lineage
The result of
extract_lineage(), or any list withnodesandedgesbuilt withcreate_table_node()andcreate_column_edge().
Value
A data frame with columns table, column, and table_type,
one row per unused column, sorted by table then column. Zero rows
when every column reaches a target.
Details
A single-query extraction usually reports nothing, because its source
nodes only carry columns the query referenced. Tables whose type is
unknown (hand-built nodes without a table_type) count as targets, on
the same reasoning as lineage_diff() severity: the graph cannot see
who consumes them, so their columns, and columns feeding them, are
not called unused.
See also
Other lineage accessors:
lineage_check(),
lineage_diff(),
lineage_edges(),
lineage_tables(),
lineage_upstream()
Examples
lineage <- list(
nodes = list(
create_table_node("orders", c("order_id", "amount", "internal_note")),
create_table_node("daily_totals", "total", table_type = "target")
),
edges = list(
create_column_edge("orders", "amount", "daily_totals", "total")
)
)
lineage_unused(lineage)
#> table column table_type
#> 1 orders internal_note source
#> 2 orders order_id source