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Merged
e10v merged 1 commit into from
Jul 11, 2026
Merged

perf: precompute centered products for fallback aggregates #326

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45 changes: 23 additions & 22 deletions src/tea_tasting/backends/ibis.py
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Original file line number Diff line number Diff line change
Expand Up @@ -25,9 +25,8 @@
import tea_tasting.aggr # noqa: TC004


_CENTERED = "__centered__{}__"
_CENTERED_LEFT = "__centered__left__{}__{}__"
_CENTERED_RIGHT = "__centered_right__{}__{}__"
_CENTERED_SQUARE = "__centered_square__{}__"
_CENTERED_PRODUCT = "__centered_product__{}__{}__"


class IbisTable(BaseTable): # noqa: D101
Expand Down Expand Up @@ -176,7 +175,7 @@ def _aggregate(
fallback_var_cols = () if ibis_table.has_var else aggr_cols.var_cols
fallback_cov_cols = () if ibis_table.has_cov else aggr_cols.cov_cols
if len(fallback_var_cols) > 0 or len(fallback_cov_cols) > 0:
data = _add_centered_cols(
data = _add_centered_product_cols(
data=data,
aggr_cols=aggr_cols,
group_col=group_col,
Expand All @@ -195,7 +194,7 @@ def _aggregate(
return _get_aggregates(result, aggr_cols, group_col)


def _add_centered_cols(
def _add_centered_product_cols(
data: ibis.expr.types.Table,
aggr_cols: tea_tasting.aggr.AggrCols,
group_col: str | None,
Expand All @@ -218,18 +217,25 @@ def _add_centered_cols(
for col in var_cols:
col_expr = data[col].cast("float")
centered_col_expr = col_expr - _mean_over(data, col_expr, group_col)
exprs.append(centered_col_expr.name(_CENTERED.format(col)))
exprs.append(
(centered_col_expr * centered_col_expr)
.name(_CENTERED_SQUARE.format(col)),
)

for left, right in cov_cols:
valid = data[left].notnull() & data[right].notnull()
left_expr = data[left].cast("float")
right_expr = data[right].cast("float")
exprs.extend((
(left_expr - _mean_over(data, valid.ifelse(left_expr, null), group_col))
.name(_CENTERED_LEFT.format(left, right)),
(right_expr - _mean_over(data, valid.ifelse(right_expr, null), group_col))
.name(_CENTERED_RIGHT.format(left, right)),
))
centered_left = (
left_expr - _mean_over(data, valid.ifelse(left_expr, null), group_col)
)
centered_right = (
right_expr - _mean_over(data, valid.ifelse(right_expr, null), group_col)
)
exprs.append(
(centered_left * centered_right)
.name(_CENTERED_PRODUCT.format(left, right)),
)
return data.select(*exprs)


Expand Down Expand Up @@ -278,9 +284,7 @@ def _sample_var(
) -> ibis.expr.types.Value:
if has_var:
return data[col].cast("float").var(how="sample")
return _fallback_sample_aggr(
data[_CENTERED.format(col)] * data[_CENTERED.format(col)],
)
return _fallback_sample_aggr(data[_CENTERED_SQUARE.format(col)])


def _sample_cov(
Expand All @@ -292,16 +296,13 @@ def _sample_cov(
) -> ibis.expr.types.Value:
if has_cov:
return data[left].cast("float").cov(data[right].cast("float"), how="sample")
return _fallback_sample_aggr(
data[_CENTERED_LEFT.format(left, right)] *
data[_CENTERED_RIGHT.format(left, right)],
)
return _fallback_sample_aggr(data[_CENTERED_PRODUCT.format(left, right)])


def _fallback_sample_aggr(
centered_expr: ibis.expr.types.Column,
product_expr: ibis.expr.types.Column,
) -> ibis.expr.types.Value:
import ibis # noqa: PLC0415

count = centered_expr.count()
return (count > 1).ifelse(centered_expr.sum() / (count - 1), ibis.null()) # ty:ignore[unsupported-operator]
count = product_expr.count()
return (count > 1).ifelse(product_expr.sum() / (count - 1), ibis.null()) # ty:ignore[unsupported-operator]
14 changes: 7 additions & 7 deletions src/tea_tasting/backends/narwhals.py
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Original file line number Diff line number Diff line change
Expand Up @@ -30,7 +30,7 @@
type CovarianceSupport = Literal["full", "ungrouped_only", "none", "auto"]


_CROSS_PRODUCT = "__cross_product__{}__{}__"
_CENTERED_PRODUCT = "__centered_product__{}__{}__"
_COV_COUNT = "__cov_count__{}__{}__"
_COV_SUM = "__cov_sum__{}__{}__"

Expand Down Expand Up @@ -185,7 +185,7 @@ def _aggregate(
narwhals_frame.cov == "ungrouped_only" and group_col is None
)
if not has_cov and len(aggr_cols.cov_cols) > 0:
frame = _add_cross_product_cols(frame, aggr_cols, group_col)
frame = _add_centered_product_cols(frame, aggr_cols, group_col)

exprs = _aggr_exprs(aggr_cols, has_cov=has_cov)
frame = (
Expand All @@ -200,7 +200,7 @@ def _aggregate(
return _get_aggregates(rows, aggr_cols, group_col)


def _add_cross_product_cols(
def _add_centered_product_cols(
frame: nw.LazyFrame,
aggr_cols: tea_tasting.aggr.AggrCols,
group_col: str | None,
Expand All @@ -221,7 +221,7 @@ def _add_cross_product_cols(
centered_cols.append(valid_col - mean)
exprs.append(
(centered_cols[0] * centered_cols[1]).alias(
_CROSS_PRODUCT.format(left, right),
_CENTERED_PRODUCT.format(left, right),
),
)
return frame.select(*exprs)
Expand All @@ -248,10 +248,10 @@ def _aggr_exprs(
)
else:
for left, right in aggr_cols.cov_cols:
cross_product = nw.col(_CROSS_PRODUCT.format(left, right))
centered_product = nw.col(_CENTERED_PRODUCT.format(left, right))
exprs.extend((
cross_product.sum().alias(_COV_SUM.format(left, right)),
cross_product.count().alias(_COV_COUNT.format(left, right)),
centered_product.sum().alias(_COV_SUM.format(left, right)),
centered_product.count().alias(_COV_COUNT.format(left, right)),
))
return exprs

Expand Down
50 changes: 22 additions & 28 deletions src/tea_tasting/backends/sql.py
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Original file line number Diff line number Diff line change
Expand Up @@ -137,9 +137,8 @@
) | {"singlestore"}

_SUBQUERY = "__subquery__"
_CENTERED = "__centered__{}__"
_CENTERED_LEFT = "__centered__left__{}__{}__"
_CENTERED_RIGHT = "__centered_right__{}__{}__"
_CENTERED_SQUARE = "__centered_square__{}__"
_CENTERED_PRODUCT = "__centered_product__{}__{}__"


class SQLQuery(BaseTable): # noqa: D101
Expand Down Expand Up @@ -318,7 +317,7 @@ def _aggregate(
fallback_var_cols = () if sql_query.var else aggr_cols.var_cols
fallback_cov_cols = () if sql_query.cov else aggr_cols.cov_cols
if len(fallback_var_cols) > 0 or len(fallback_cov_cols) > 0:
query = _add_centered_cols(
query = _add_centered_product_cols(
query=query,
aggr_cols=aggr_cols,
group_col=group_col,
Expand All @@ -341,7 +340,7 @@ def _aggregate(
return _get_aggregates(data, aggr_cols, group_col)


def _add_centered_cols(
def _add_centered_product_cols(
query: sqlglot.exp.Subquery,
aggr_cols: tea_tasting.aggr.AggrCols,
group_col: str | None,
Expand All @@ -358,13 +357,14 @@ def _add_centered_cols(
keep_cols.add(group_col)

exprs: list[sqlglot.exp.Expression] = [_col(col) for col in keep_cols]
exprs.extend(
sqlglot.exp.alias_(
_float(col) - _mean_over(_float(col), group_col),
_CENTERED.format(col),
for col in var_cols:
centered = _float(col) - _mean_over(_float(col), group_col)
exprs.append(
sqlglot.exp.alias_(
centered * centered.copy(),
_CENTERED_SQUARE.format(col),
),
)
for col in var_cols
)
for left, right in cov_cols:
valid = (
_col(left).is_(sqlglot.exp.Null()).not_() &
Expand All @@ -374,16 +374,14 @@ def _add_centered_cols(
right_float = _float(right)
left_valid = _if_valid(valid, left_float.copy())
right_valid = _if_valid(valid, right_float.copy())
exprs.extend((
sqlglot.exp.alias_(
left_float - _mean_over(left_valid, group_col),
_CENTERED_LEFT.format(left, right),
),
centered_left = left_float - _mean_over(left_valid, group_col)
centered_right = right_float - _mean_over(right_valid, group_col)
exprs.append(
sqlglot.exp.alias_(
right_float - _mean_over(right_valid, group_col),
_CENTERED_RIGHT.format(left, right),
centered_left * centered_right,
_CENTERED_PRODUCT.format(left, right),
),
))
)
return sqlglot.exp.select(*exprs).from_(query).subquery(_SUBQUERY)


Expand Down Expand Up @@ -422,8 +420,7 @@ def _sample_var(col: str, *, var: bool | str) -> sqlglot.exp.Expression:
return sqlglot.exp.Variance(this=_float(col))
if isinstance(var, str):
return sqlglot.exp.Anonymous(this=var, expressions=[_float(col)])
centered = _col(_CENTERED.format(col))
return _fallback_sample_aggr(centered * centered)
return _fallback_sample_aggr(_col(_CENTERED_SQUARE.format(col)))


def _sample_cov(
Expand All @@ -439,20 +436,17 @@ def _sample_cov(
this=cov,
expressions=[_float(left), _float(right)],
)
return _fallback_sample_aggr(
_col(_CENTERED_LEFT.format(left, right)) *
_col(_CENTERED_RIGHT.format(left, right)),
)
return _fallback_sample_aggr(_col(_CENTERED_PRODUCT.format(left, right)))


def _fallback_sample_aggr(
centered_expr: sqlglot.exp.Expression,
product_expr: sqlglot.exp.Expression,
) -> sqlglot.exp.Expression:
count = sqlglot.exp.Count(this=centered_expr.copy())
count = sqlglot.exp.Count(this=product_expr.copy())
one = sqlglot.exp.Literal.number(1)
return sqlglot.exp.Case().when(
count > one,
sqlglot.exp.Sum(this=centered_expr) / (count.copy() - one.copy()),
sqlglot.exp.Sum(this=product_expr) / (count.copy() - one.copy()),
).else_(sqlglot.exp.Null())


Expand Down
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