Comparison.n_failed

The number of test units that failed.

Comparison.n_failed: int

A test unit fails if its status is "changed", "missing", "extra", or "dup_key". If the schema check failed (see schema_ok), every test unit fails, so n_failed equals n. It’s always n - n_passed.

A count of zero failures, along with a passing schema check, is what makes a comparison identical. To see how the failures break down by status, use status_counts.

Examples

One station’s reading changed, one station was dropped, and one was added.

import pointblank as pb
import polars as pl

readings_v1 = pl.DataFrame(
    {"station": ["S1", "S2", "S3", "S4"], "temp": [12.1, 14.0, 9.8, 11.2]}
)
readings_v2 = pl.DataFrame(
    {"station": ["S1", "S2", "S3", "S5"], "temp": [12.1, 14.3, 9.8, 8.0]}
)

comparison = pb.compare(readings_v1, readings_v2, keys="station")

comparison.n_failed

3

A count is useful for a quick check, for instance to stop a script when too many rows differ:

if comparison.n_failed > 0.25 * comparison.n:
    print(f"{comparison.n_failed} of {comparison.n} rows differ")

3 of 5 rows differ

To act on failures with thresholds and actions instead, compare the tables in a validation with Validate.tbl_match().