Declare a validation rule

Builds a rule for validate_rules(): a predicate over one column, or over the whole data frame, with a severity and a message. Rules live alongside a schema in a provenance record, which keeps the project-specific checks in data rather than scattered through code.

Usage

rule(
  name,
  expr,
  column = NULL,
  severity = c("warning", "fatal"),
  message = NULL
)

Arguments

name

Short identifier for the rule.

expr

A function, as described above.

column

Column the rule applies to, or NULL for a table-level rule.

severity

"warning" (default) or "fatal".

message

Human-readable description of what a failure means. Defaults to a generated one naming the rule.

Value

A list of class bricklayer_rule.

Details

expr is a function. Given column, it receives that column and must return a logical vector the same length (TRUE = the row passes) or a single logical for a whole-column property. Given no column, it receives the whole data frame and must return a single logical.

See also

validate_rules(), validate_schema() for the structural checks that need no rules.

Examples

# A column predicate, applied row-wise.
rule("age_non_negative", function(v) v >= 0, column = "age")
#> <rule> age_non_negative [warning] on `age`

# A whole-column property.
rule("id_unique", function(v) !anyDuplicated(v), column = "id",
     severity = "fatal")
#> <rule> id_unique [fatal] on `id`

# A table-level rule spanning two columns.
rule("dates_ordered", function(df) all(df$start <= df$end))
#> <rule> dates_ordered [warning] table-level