feat[next]: concat_where embedded (limited to 1D)

pyproject.toml

@@ -318,6 +318,7 @@ markers = [
   'uses_max_over: tests that use the max_over builtin',
   'uses_mesh_with_skip_values: tests that use a mesh with skip values',
   'uses_concat_where: tests that use the concat_where builtin',
+  'embedded_concat_where_infinite_domain: tests with concat_where resulting in an infinite domain',
   'uses_program_metrics: tests that require backend support for program metrics',
   'uses_program_with_sliced_out_arguments: tests that use a sliced argument which is not supported for non-mutable arrays, e.g. JAX',
   'checks_specific_error: tests that rely on the backend to produce a specific error message'

src/gt4py/next/embedded/nd_array_field.py

@@ -18,16 +18,7 @@
 from numpy import typing as npt
 
 from gt4py._core import definitions as core_defs
-from gt4py.eve.extended_typing import (
-    ClassVar,
-    Iterable,
-    Never,
-    Optional,
-    ParamSpec,
-    TypeAlias,
-    TypeVar,
-    cast,
-)
+from gt4py.eve.extended_typing import ClassVar, Never, Optional, ParamSpec, TypeAlias, TypeVar, cast
 from gt4py.next import common, utils
 from gt4py.next.embedded import (
     common as embedded_common,
@@ -820,39 +811,6 @@ def _hyperslice(
 NdArrayField.register_builtin_func(fbuiltins.where, _make_builtin("where", "where"))
 
 
-def _compute_mask_slices(
-    mask: core_defs.NDArrayObject,
-) -> list[tuple[bool, slice]]:
-    """Take a 1-dimensional mask and return a sequence of mappings from boolean values to slices."""
-    # TODO: does it make sense to upgrade this naive algorithm to numpy?
-    assert mask.ndim == 1
-    cur = bool(mask[0].item())
-    ind = 0
-    res = []
-    for i in range(1, mask.shape[0]):
-        # Use `.item()` to extract the scalar from a 0-d array in case of e.g. cupy
-        if (mask_i := bool(mask[i].item())) != cur:
-            res.append((cur, slice(ind, i)))
-            cur = mask_i
-            ind = i
-    res.append((cur, slice(ind, mask.shape[0])))
-    return res
-
-
-def _trim_empty_domains(
-    lst: Iterable[tuple[bool, common.Domain]],
-) -> list[tuple[bool, common.Domain]]:
-    """Remove empty domains from beginning and end of the list."""
-    lst = list(lst)
-    if not lst:
-        return lst
-    if lst[0][1].is_empty():
-        return _trim_empty_domains(lst[1:])
-    if lst[-1][1].is_empty():
-        return _trim_empty_domains(lst[:-1])
-    return lst
-
-
 def _to_field(
     value: common.Field | core_defs.Scalar, nd_array_field_type: type[NdArrayField]
 ) -> common.Field:
@@ -906,85 +864,95 @@ def _stack_domains(*domains: common.Domain, dim: common.Dimension) -> Optional[c
 
 def _concat(*fields: common.Field, dim: common.Dimension) -> common.Field:
     # TODO(havogt): this function could be extended to a general concat
-    # currently only concatenate along the given dimension and requires the fields to be ordered
+    # currently only concatenate along the given dimension
+    sorted_fields = sorted(fields, key=lambda f: f.domain[dim].unit_range.start)
 
     if (
-        len(fields) > 1
-        and not embedded_common.domain_intersection(*[f.domain for f in fields]).is_empty()
+        len(sorted_fields) > 1
+        and not embedded_common.domain_intersection(*[f.domain for f in sorted_fields]).is_empty()
     ):
         raise ValueError("Fields to concatenate must not overlap.")
-    new_domain = _stack_domains(*[f.domain for f in fields], dim=dim)
+    new_domain = _stack_domains(*[f.domain for f in sorted_fields], dim=dim)
     if new_domain is None:
         raise embedded_exceptions.NonContiguousDomain(f"Cannot concatenate fields along {dim}.")
-    nd_array_class = _get_nd_array_class(*fields)
+    nd_array_class = _get_nd_array_class(*sorted_fields)
     return nd_array_class.from_array(
         nd_array_class.array_ns.concatenate(
-            [nd_array_class.array_ns.broadcast_to(f.ndarray, f.domain.shape) for f in fields],
+            [
+                nd_array_class.array_ns.broadcast_to(f.ndarray, f.domain.shape)
+                for f in sorted_fields
+            ],
             axis=new_domain.dim_index(dim, allow_missing=False),
         ),
         domain=new_domain,
     )
 
 
+def _invert_domain(domain: common.Domain) -> tuple[common.Domain, ...]:
+    assert domain.ndim == 1
+    dim = domain.dims[0]
+    rng = domain.ranges[0]
+
+    result = []
+    if rng.start is not common.Infinity.NEGATIVE:
+        result.append(
+            common.Domain(
+                dims=(dim,), ranges=(common.UnitRange(common.Infinity.NEGATIVE, rng.start),)
+            )
+        )
+    if rng.stop is not common.Infinity.POSITIVE:
+        result.append(
+            common.Domain(
+                dims=(dim,), ranges=(common.UnitRange(rng.stop, common.Infinity.POSITIVE),)
+            )
+        )
+    return tuple(result)
+
+
+def _size0_field(
+    nd_array_class: type[NdArrayField], dims: tuple[common.Dimension, ...], dtype: core_defs.DType
+) -> NdArrayField:
+    return nd_array_class.from_array(
+        nd_array_class.array_ns.empty((0,) * len(dims), dtype=dtype.scalar_type),
+        domain=common.Domain(dims=dims, ranges=(common.UnitRange(0, 0),) * len(dims)),
+    )
+
+
 def _concat_where(
-    mask_field: common.Field, true_field: common.Field, false_field: common.Field
+    mask: common.Domain,
+    true_field: common.Field,
+    false_field: common.Field,
 ) -> common.Field:
-    cls_ = _get_nd_array_class(mask_field, true_field, false_field)
-    xp = cls_.array_ns
-    if mask_field.domain.ndim != 1:
+    if mask.ndim != 1:
         raise NotImplementedError(
             "'concat_where': Can only concatenate fields with a 1-dimensional mask."
         )
-    mask_dim = mask_field.domain.dims[0]
+    mask_dim = mask.dims[0]
 
     # intersect the field in dimensions orthogonal to the mask, then all slices in the mask field have same domain
     t_broadcasted, f_broadcasted = _intersect_fields(true_field, false_field, ignore_dims=mask_dim)
 
-    # TODO(havogt): for clarity, most of it could be implemented on named_range in the masked dimension, but we currently lack the utils
-    # compute the consecutive ranges (first relative, then domain) of true and false values
-    mask_values_to_slices_mapping: Iterable[tuple[bool, slice]] = _compute_mask_slices(
-        mask_field.ndarray
-    )
-    mask_values_to_domain_mapping: Iterable[tuple[bool, common.Domain]] = (
-        (mask, mask_field.domain.slice_at[domain_slice])
-        for mask, domain_slice in mask_values_to_slices_mapping
-    )
-    # mask domains intersected with the respective fields
-    mask_values_to_intersected_domains_mapping: Iterable[tuple[bool, common.Domain]] = (
-        (
-            mask_value,
-            embedded_common.domain_intersection(
-                t_broadcasted.domain if mask_value else f_broadcasted.domain, mask_domain
-            ),
-        )
-        for mask_value, mask_domain in mask_values_to_domain_mapping
-    )
+    true_domain = embedded_common.domain_intersection(t_broadcasted.domain, mask)
+    t_slices = () if true_domain.is_empty() else (t_broadcasted[true_domain],)
 
-    # remove the empty domains from the beginning and end
-    mask_values_to_intersected_domains_mapping = _trim_empty_domains(
-        mask_values_to_intersected_domains_mapping
+    inverted_masks = _invert_domain(mask)
+    false_domains = tuple(
+        intersection
+        for d in inverted_masks
+        if not (
+            intersection := embedded_common.domain_intersection(f_broadcasted.domain, d)
+        ).is_empty()
     )
-    if any(d.is_empty() for _, d in mask_values_to_intersected_domains_mapping):
-        raise embedded_exceptions.NonContiguousDomain(
-            f"In 'concat_where', cannot concatenate the following 'Domain's: {[d for _, d in mask_values_to_intersected_domains_mapping]}."
-        )
-
-    # slice the fields with the domain ranges
-    transformed = [
-        t_broadcasted[d] if v else f_broadcasted[d]
-        for v, d in mask_values_to_intersected_domains_mapping
-    ]
+    f_slices = tuple(f_broadcasted[d] for d in false_domains)
 
-    # stack the fields together
-    if transformed:
-        return _concat(*transformed, dim=mask_dim)
-    else:
-        result_domain = common.Domain(common.NamedRange(mask_dim, common.UnitRange(0, 0)))
-        result_array = xp.empty(result_domain.shape)
-    return cls_.from_array(result_array, domain=result_domain)
+    if len(t_slices) + len(f_slices) == 0:
+        # no data to concatenate, return an empty field
+        nd_array_class = _get_nd_array_class(true_field, false_field)
+        return _size0_field(nd_array_class, dims=t_broadcasted.domain.dims, dtype=true_field.dtype)
+    return _concat(*f_slices, *t_slices, dim=mask_dim)
 
 
-NdArrayField.register_builtin_func(experimental.concat_where, _concat_where)  # type: ignore[arg-type] # TODO(havogt): this is still the "old" concat_where, needs to be replaced in a next PR
+NdArrayField.register_builtin_func(experimental.concat_where, _concat_where)  # type: ignore[arg-type]
 
 
 def _make_reduction(

src/gt4py/next/ffront/experimental.py

@@ -25,25 +25,25 @@ def concat_where(
     false_field: common.Field | core_defs.ScalarT | Tuple | named_collections.CustomNamedCollection,
     /,
 ) -> common.Field | Tuple:
-    """
-    Concatenates two field fields based on a 1D mask.
-
-    The resulting domain is the concatenation of the mask subdomains with the domains of the respective true or false fields.
-    Empty domains at the beginning or end are ignored, but the interior must result in a consecutive domain.
-
-    TODO(havogt): I can't get this doctest to run, even after copying the __doc__ in the decorator
-    Example:
-        >>> I = common.Dimension("I")
-        >>> mask = common._field([True, False, True], domain={I: (0, 3)})
-        >>> true_field = common._field([1, 2], domain={I: (0, 2)})
-        >>> false_field = common._field([3, 4, 5], domain={I: (1, 4)})
-        >>> assert concat_where(mask, true_field, false_field) == _field([1, 3], domain={I: (0, 2)})
-
-        >>> mask = common._field([True, False, True], domain={I: (0, 3)})
-        >>> true_field = common._field([1, 2, 3], domain={I: (0, 3)})
-        >>> false_field = common._field(
-        ...     [4], domain={I: (2, 3)}
-        ... )  # error because of non-consecutive domain: missing I(1), but has I(0) and I(2) values
+    """Assemble a field by selecting from ``true_field`` where ``cond`` applies and from ``false_field`` elsewhere.
+
+    Unlike ``where`` (element-wise selection via a boolean mask field), ``concat_where``
+    works on **domain regions**: the condition is a ``Domain`` (not a ``Field``), and the
+    result is the concatenation of slices from the two fields along one dimension.
+    Each field only needs to cover its own region — they may be non-overlapping.
+
+    The condition must be a 1D ``Domain`` (e.g. ``I < 5``).
+
+    Args:
+        cond: 1D Domain specifying the "true" region.
+        true_field: Field (or scalar) providing values inside the domain region.
+        false_field: Field (or scalar) providing values outside the domain region.
+
+    Returns:
+        A new field whose domain is the concatenation of the contributed regions.
+
+    Raises:
+        NonContiguousDomain: If the resulting domain has interior gaps.
     """
     raise NotImplementedError()
 

tests/next_tests/definitions.py

@@ -125,6 +125,7 @@ class ProgramFormatterId(_PythonObjectIdMixin, str, enum.Enum):
 USES_PROGRAM_METRICS = "uses_program_metrics"
 USES_SCALAR_IN_DOMAIN_AND_FO = "uses_scalar_in_domain_and_fo"
 USES_CONCAT_WHERE = "uses_concat_where"
+EMBEDDED_CONCAT_WHERE_INFINITE_DOMAIN = "embedded_concat_where_infinite_domain"
 USES_PROGRAM_WITH_SLICED_OUT_ARGUMENTS = "uses_program_with_sliced_out_arguments"
 CHECKS_SPECIFIC_ERROR = "checks_specific_error"
 
@@ -167,7 +168,7 @@ class ProgramFormatterId(_PythonObjectIdMixin, str, enum.Enum):
         XFAIL,
         UNSUPPORTED_MESSAGE,
     ),  # we can't extract the field type from scan args
-    (USES_CONCAT_WHERE, XFAIL, UNSUPPORTED_MESSAGE),
+    (EMBEDDED_CONCAT_WHERE_INFINITE_DOMAIN, XFAIL, UNSUPPORTED_MESSAGE),
 ]
 JAX_EMBEDDED_SKIP_LIST = EMBEDDED_SKIP_LIST + [
     (USES_PROGRAM_WITH_SLICED_OUT_ARGUMENTS, XFAIL, UNSUPPORTED_MESSAGE),
@@ -179,7 +180,7 @@ class ProgramFormatterId(_PythonObjectIdMixin, str, enum.Enum):
     (USES_CONCAT_WHERE, XFAIL, UNSUPPORTED_MESSAGE),
 ]
 GTIR_EMBEDDED_SKIP_LIST = ROUNDTRIP_SKIP_LIST + [
-    (USES_CONCAT_WHERE, XFAIL, UNSUPPORTED_MESSAGE),
+    (EMBEDDED_CONCAT_WHERE_INFINITE_DOMAIN, XFAIL, UNSUPPORTED_MESSAGE),
 ]
 GTFN_SKIP_TEST_LIST = (
     COMMON_SKIP_TEST_LIST