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ndarray: accept axis: on reductions and cumsum #883

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tannevaled merged 3 commits into from
Nov 4, 2026
Merged

ndarray: accept axis: on reductions and cumsum #883

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2b0e264
ndarray: accept axis: on reductions and cumsum, as NumPy spells it
tannevaled Nov 3, 2026
8ddfcb5
Merge remote-tracking branch 'origin/main' into ndarray-kwargs
tannevaled Nov 3, 2026
95a6e66
Merge remote-tracking branch 'origin/main' into ndarray-kwargs
tannevaled Nov 4, 2026
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38 changes: 28 additions & 10 deletions internal/vm/ndarray.go
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Original file line number Diff line number Diff line change
Expand Up @@ -19,8 +19,8 @@ import (
// The Ruby surface is the one the go-ndarray playground's code generator emits
// (Go | Ruby | NumPy): creation (zeros/ones/full/arange/linspace/eye/from),
// views (reshape/transpose/flatten/squeeze/expand_dims and NumPy basic indexing
// through #[]), elementwise ufuncs and **, reductions with an axis and
// keepdims:, products and joins. Semantics are go-ndarray's, which are NumPy's,
// through #[]), elementwise ufuncs and **, reductions with an axis (positional,
// a.sum(0), or NumPy's keyword, a.sum(axis: 0)) and keepdims:, products and joins. Semantics are go-ndarray's, which are NumPy's,
// in float64.
//
// Every method checks its own arguments. A wrong count raises ArgumentError, a
Expand Down Expand Up @@ -167,6 +167,23 @@ func ndKeep(kw map[string]object.Value) bool {
return ok && v.Truthy()
}

// ndOptAxis reads the optional axis of a reduction, given positionally (a.sum(0))
// or as NumPy's keyword (a.sum(axis: 0)). Absent or nil means no axis; giving
// both forms is an ArgumentError, as NumPy's duplicate argument is a TypeError.
func (vm *VM) ndOptAxis(args []object.Value, kw map[string]object.Value) (int, bool) {
v, ok := kw["axis"]
if len(args) == 1 {
if ok {
raise("ArgumentError", "axis given both positionally and as a keyword")
}
v, ok = args[0], true
}
if !ok || object.IsNil(v) {
return 0, false
}
return vm.ndInt(v), true
}

// ndOnes is the all-ones shape of the given rank: what a whole-array reduction
// with keepdims: true leaves.
func ndOnes(ndim int) []int {
Expand Down Expand Up @@ -549,11 +566,11 @@ func (vm *VM) registerNDArray() {
// the reduced axes as length 1 (all of them when there is no axis).
reduce := func(name string, whole func(*nd.Array) (float64, error), along func(*nd.Array, int, bool) (*nd.Array, error)) {
d(name, func(vm *VM, v object.Value, args []object.Value, _ *Proc) object.Value {
args, kw := ndKw(args, "keepdims")
args, kw := ndKw(args, "axis", "keepdims")
ndArgc(args, 0, 1)
a, keep := self(v), ndKeep(kw)
if len(args) == 1 && !object.IsNil(args[0]) {
return mustArray(along(a, vm.ndInt(args[0]), keep))
if axis, ok := vm.ndOptAxis(args, kw); ok {
return mustArray(along(a, axis, keep))
}
r, err := whole(a)
if err != nil {
Expand All @@ -578,11 +595,11 @@ func (vm *VM) registerNDArray() {
// indices along the axis.
argReduce := func(name string, whole func(*nd.Array) (int, error), along func(*nd.Array, int, bool) (*nd.Array, error)) {
d(name, func(vm *VM, v object.Value, args []object.Value, _ *Proc) object.Value {
args, kw := ndKw(args, "keepdims")
args, kw := ndKw(args, "axis", "keepdims")
ndArgc(args, 0, 1)
a, keep := self(v), ndKeep(kw)
if len(args) == 1 && !object.IsNil(args[0]) {
return mustArray(along(a, vm.ndInt(args[0]), keep))
if axis, ok := vm.ndOptAxis(args, kw); ok {
return mustArray(along(a, axis, keep))
}
i, err := whole(a)
if err != nil {
Expand All @@ -599,9 +616,10 @@ func (vm *VM) registerNDArray() {

// cumsum: flattened with no axis, else along the axis.
d("cumsum", func(vm *VM, v object.Value, args []object.Value, _ *Proc) object.Value {
args, kw := ndKw(args, "axis")
ndArgc(args, 0, 1)
if len(args) == 1 && !object.IsNil(args[0]) {
return mustArray(self(v).CumSum(vm.ndInt(args[0])))
if axis, ok := vm.ndOptAxis(args, kw); ok {
return mustArray(self(v).CumSum(axis))
}
return &NDArray{a: self(v).CumSumFlat()}
})
Expand Down
50 changes: 49 additions & 1 deletion internal/vm/ndarray_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -548,7 +548,13 @@ func TestNDArrayArgumentChecks(t *testing.T) {
{`NDArray.zeros(2, 0).max(1)`, "ArgumentError", "zero-length axis"},
{a + `a.argmax(1, 2)`, "ArgumentError", "(given 2, expected 0..1)"},
{a + `a.argmax("x")`, "TypeError", "String into Integer"},
{a + `a.argmin(axis: 1)`, "ArgumentError", "unknown keyword: :axis"},
{a + `a.argmin(axes: 1)`, "ArgumentError", "unknown keyword: :axes"},
{a + `a.sum(0, axis: 1)`, "ArgumentError", "both positionally and as a keyword"},
{a + `a.argmax(0, axis: 1)`, "ArgumentError", "both positionally and as a keyword"},
{a + `a.cumsum(0, axis: 1)`, "ArgumentError", "both positionally and as a keyword"},
{a + `a.sum(axis: "x")`, "TypeError", "String into Integer"},
{a + `a.sum(axis: 2)`, "IndexError", "axis out of range"},
{a + `a.cumsum(axes: 1)`, "ArgumentError", "unknown keyword: :axes"},
{a + `a.argmax(4)`, "IndexError", "axis out of range"},
{`NDArray.zeros(0).argmin(keepdims: true)`, "ArgumentError", "empty"},
{a + `a.cumsum(1, 2)`, "ArgumentError", "(given 2, expected 0..1)"},
Expand Down Expand Up @@ -585,3 +591,45 @@ func TestNDArrayArgumentChecks(t *testing.T) {
}
}
}

// TestNDArrayAxisKeyword: NumPy spells the axis as a keyword (a.sum(axis=0)), so
// a Ruby user writes a.sum(axis: 0). Before, only keepdims: was accepted and
// axis: raised "unknown keyword: :axis". Values are NumPy's, by hand, for
// a = arange(6).reshape(2, 3) = [[0,1,2],[3,4,5]]. The positional form stays.
func TestNDArrayAxisKeyword(t *testing.T) {
const a = `a = NDArray.arange(6).reshape(2, 3); `
for _, c := range []struct{ src, want string }{
// a.sum(axis=0) == [3, 5, 7]; a.sum(axis=1) == [3, 12].
{a + `p a.sum(axis: 0).to_a`, "[3.0, 5.0, 7.0]\n"},
{a + `p a.sum(axis: 1).to_a`, "[3.0, 12.0]\n"},
{a + `p a.sum(axis: -1).to_a`, "[3.0, 12.0]\n"},
// Control: the positional form gives the same answers.
{a + `p a.sum(0).to_a`, "[3.0, 5.0, 7.0]\n"},
{a + `p a.sum(1).to_a`, "[3.0, 12.0]\n"},
// a.sum(axis=1, keepdims=True).shape == (2, 1), in either order of keywords.
{a + `p a.sum(axis: 1, keepdims: true).shape`, "[2, 1]\n"},
{a + `p a.sum(keepdims: true, axis: 1).shape`, "[2, 1]\n"},
{a + `p a.sum(1, keepdims: true).shape`, "[2, 1]\n"},
// axis=None (nil) is the whole array.
{a + `p a.sum(axis: nil)`, "15.0\n"},
{a + `p a.sum(axis: nil, keepdims: true).shape`, "[1, 1]\n"},
{a + `p a.sum`, "15.0\n"},
// The other reductions.
{a + `p a.mean(axis: 0).to_a`, "[1.5, 2.5, 3.5]\n"},
{a + `p a.prod(axis: 1).to_a`, "[0.0, 60.0]\n"},
{a + `p a.max(axis: 1).to_a`, "[2.0, 5.0]\n"},
{a + `p a.min(axis: 0).to_a`, "[0.0, 1.0, 2.0]\n"},
{a + `p a.argmax(axis: 1).to_a`, "[2.0, 2.0]\n"},
{a + `p a.argmin(axis: 0).to_a`, "[0.0, 0.0, 0.0]\n"},
{a + `p a.argmax(1).to_a`, "[2.0, 2.0]\n"},
{a + `p a.argmax(axis: nil)`, "5\n"},
// cumsum(axis=0) == [[0,1,2],[3,5,7]]; no axis flattens.
{a + `p a.cumsum(axis: 0).to_a`, "[0.0, 1.0, 2.0, 3.0, 5.0, 7.0]\n"},
{a + `p a.cumsum(0).to_a`, "[0.0, 1.0, 2.0, 3.0, 5.0, 7.0]\n"},
{a + `p a.cumsum.to_a`, "[0.0, 1.0, 3.0, 6.0, 10.0, 15.0]\n"},
} {
if got := eval(t, c.src); got != c.want {
t.Errorf("src=%q got=%q want=%q", c.src, got, c.want)
}
}
}
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