ToPackedArray

Status: Stable

documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

Description

ToPackedArray[list]

is ToNDArray[list]: it returns list stored as a dense machine-precision buffer. The result is still a List -- same Head, same printed form, same elements -- but NDArrayQ gives True for it. Provided under Mathematica's name for the same operation; see ToNDArray.

Examples (4)

Every input below was run against the current Mathilda build and its output recorded.

Basic examples (1)

In[1]:= ToPackedArray[{1., 2., 3.}] === ToNDArray[{1., 2., 3.}]
Out[1]= True

Applications (3)

Mathematica's name for ToNDArray

In[2]:= ToPackedArray[{1., 2., 3., 4.}]
Out[2]= {1.0, 2.0, 3.0, 4.0}

The result is a packed List

In[3]:= PackedArrayQ[ToPackedArray[{1., 2., 3.}]]
Out[3]= True

Literally the same operation

In[4]:= ToPackedArray[{1., 2., 3.}] === ToNDArray[{1., 2., 3.}]
Out[4]= True

Implementation notes

Algorithm. ToPackedArray is Mathematica's name (Developer​ToPackedArray) for ToNDArray and is the same C builtin (builtin_tondarray) registered under a second name — not a rule that rewrites to ToNDArray. Registering it as a genuine alias rather than a DownValue means it costs no extra evaluation pass, never shows up in traces, and cannot be shadowed by a user definition on the target. Every form and option is therefore identical to ToNDArray: an optional trailing DataType -> "..." is stripped (pack_take_dtype), the one positional argument is packed by pack_force_coerce → pack_build with no size threshold and coerce = true, so a mixed machine Integer/Real list widens to a float64 buffer while an all-integer list stays int64. ToPackedArray[list] === ToNDArray[list] by construction.

Data structures. Identical to ToNDArray: an EXPR_NDARRAY with present_as = NDA_HEAD_LIST (the packed-List surface — Head stays List), backed by a dense row-major buffer sized ndt_elem_size(dt) * n.

Complexity / limits. O(n) (sniff + flatten) and one allocation; ignores the automatic-packing threshold; rejects complex, ragged, empty, and non-machine input by returning the list unchanged. See ToNDArray for the dtype-coercion rules.

Attributes: Protected.

References

See also: ToNDArray

• Source: src/pack.c
• Specification: docs/spec/builtins/packed-arrays.md
• Tests: tests/test_elliptic_machine.c
• Tests: tests/test_erf.c
• Tests: tests/test_erfc.c
• Tests: tests/test_erfi.c

Notes & additional examples

Notes

ToPackedArray is the Wolfram Language's name (Developer​ToPackedArray) for ToNDArray, provided so code written against that name reads across. It is the same builtin registered twice, not a rule that rewrites to ToNDArray, so it costs no extra evaluation pass, never appears in a trace, and cannot be shadowed by a user definition on the other name. Every form and option is identical: it stores a rectangular machine-number list as a dense buffer (invisible except to NDArrayQ/PackedArrayQ), ignores the automatic-packing threshold, infers "int64"/"float64"/"bool", widens a mixed Integer/Real list to "float64", takes a DataType -> "..." override, and returns the list unchanged when it cannot pack. See ToNDArray for the full dtype rules.