refactor: make sum_of_deltas_squared private (#602)

Author: henryiii

docs/usage/accumulators.rst

@@ -101,7 +101,7 @@ Mean
 
 This accumulator is contained in the Mean storage, and supports Views. It
 provides three values; ``.count``, ``.value``, and ``.variance``. Internally,
-the variance is stored as ``sum_of_deltas_squared``, which is used to compute
+the variance is stored as ``_sum_of_deltas_squared``, which is used to compute
 ``variance``.
 
 For example, you could compute the mean of the following values::

include/bh_python/accumulators/mean.hpp

@@ -33,29 +33,29 @@ struct mean {
          const value_type& variance) noexcept
         : count(n)
         , value(mean)
-        , sum_of_deltas_squared(variance * (n - 1)) {}
+        , _sum_of_deltas_squared(variance * (n - 1)) {}
 
     mean(const value_type& sum,
          const value_type& mean,
-         const value_type& sum_of_deltas_squared,
+         const value_type& _sum_of_deltas_squared,
          bool /* Tag to trigger python internal constructor */)
         : count(sum)
         , value(mean)
-        , sum_of_deltas_squared(sum_of_deltas_squared) {}
+        , _sum_of_deltas_squared(_sum_of_deltas_squared) {}
 
     void operator()(const value_type& x) noexcept {
         count += static_cast<value_type>(1);
         const auto delta = x - value;
         value += delta / count;
-        sum_of_deltas_squared += delta * (x - value);
+        _sum_of_deltas_squared += delta * (x - value);
     }
 
     void operator()(const boost::histogram::weight_type<value_type>& w,
                     const value_type& x) noexcept {
         count += w.value;
         const auto delta = x - value;
         value += w.value * delta / count;
-        sum_of_deltas_squared += w.value * delta * (x - value);
+        _sum_of_deltas_squared += w.value * delta * (x - value);
     }
 
     mean& operator+=(const mean& rhs) noexcept {
@@ -69,38 +69,40 @@ struct mean {
 
         count += rhs.count;
         value = (n1 * mu1 + n2 * mu2) / count;
-        sum_of_deltas_squared += rhs.sum_of_deltas_squared;
-        sum_of_deltas_squared
+        _sum_of_deltas_squared += rhs._sum_of_deltas_squared;
+        _sum_of_deltas_squared
             += n1 * (value - mu1) * (value - mu1) + n2 * (value - mu2) * (value - mu2);
 
         return *this;
     }
 
     mean& operator*=(const value_type& s) noexcept {
         value *= s;
-        sum_of_deltas_squared *= s * s;
+        _sum_of_deltas_squared *= s * s;
         return *this;
     }
 
     bool operator==(const mean& rhs) const noexcept {
         return count == rhs.count && value == rhs.value
-               && sum_of_deltas_squared == rhs.sum_of_deltas_squared;
+               && _sum_of_deltas_squared == rhs._sum_of_deltas_squared;
     }
 
     bool operator!=(const mean& rhs) const noexcept { return !operator==(rhs); }
 
-    value_type variance() const noexcept { return sum_of_deltas_squared / (count - 1); }
+    value_type variance() const noexcept {
+        return _sum_of_deltas_squared / (count - 1);
+    }
 
     template <class Archive>
     void serialize(Archive& ar, unsigned) {
         ar& boost::make_nvp("count", count);
         ar& boost::make_nvp("value", value);
-        ar& boost::make_nvp("sum_of_deltas_squared", sum_of_deltas_squared);
+        ar& boost::make_nvp("_sum_of_deltas_squared", _sum_of_deltas_squared);
     }
 
     value_type count{};
     value_type value{};
-    value_type sum_of_deltas_squared{};
+    value_type _sum_of_deltas_squared{};
 };
 
 } // namespace accumulators

notebooks/BoostHistogramHandsOn.ipynb

@@ -884,7 +884,7 @@
        "      [(3., 0.4, 0.02), (0., 0. , 0.  ), (0., 0. , 0.  ), (0., 0. , 0.  ),\n",
        "       (0., 0. , 0.  ), (0., 0. , 0.  ), (0., 0. , 0.  ), (0., 0. , 0.  ),\n",
        "       (0., 0. , 0.  ), (0., 0. , 0.  )],\n",
-       "      dtype=[('count', '<f8'), ('value', '<f8'), ('sum_of_deltas_squared', '<f8')])"
+       "      dtype=[('count', '<f8'), ('value', '<f8'), ('_sum_of_deltas_squared', '<f8')])"
       ]
      },
      "execution_count": 36,

src/boost_histogram/_core/accumulators.pyi

@@ -79,7 +79,7 @@ class Mean(_BaseAccumulator):
     @property
     def value(self) -> float: ...
     @property
-    def sum_of_deltas_squared(self) -> float: ...
+    def _sum_of_deltas_squared(self) -> float: ...
     @property
     def variance(self) -> float: ...
     def __call__(

src/boost_histogram/_internal/view.py

@@ -219,20 +219,20 @@ def variance(self) -> np.ndarray:
             )
 
 
-@fields("count", "value", "sum_of_deltas_squared")
+@fields("count", "value", "_sum_of_deltas_squared")
 class MeanView(View):
     __slots__ = ()
     _PARENT = Mean
 
     count: np.ndarray
     value: np.ndarray
-    sum_of_deltas_squared: np.ndarray
+    _sum_of_deltas_squared: np.ndarray
 
     # Variance is a computation
     @property
     def variance(self) -> np.ndarray:
         with np.errstate(divide="ignore", invalid="ignore"):
-            return self["sum_of_deltas_squared"] / (self["count"] - 1)  # type: ignore
+            return self["_sum_of_deltas_squared"] / (self["count"] - 1)  # type: ignore
 
 
 def _to_view(

src/register_accumulators.cpp

@@ -263,7 +263,7 @@ void register_accumulators(py::module& accumulators) {
         ;
 
     using mean = accumulators::mean<double>;
-    PYBIND11_NUMPY_DTYPE(mean, count, value, sum_of_deltas_squared);
+    PYBIND11_NUMPY_DTYPE(mean, count, value, _sum_of_deltas_squared);
 
     register_accumulator<mean>(accumulators, "Mean", py::buffer_protocol())
         .def_buffer(make_buffer<mean>())
@@ -275,7 +275,7 @@ void register_accumulators(py::module& accumulators) {
 
         .def_readonly("count", &mean::count)
         .def_readonly("value", &mean::value)
-        .def_readonly("sum_of_deltas_squared", &mean::sum_of_deltas_squared)
+        .def_readonly("_sum_of_deltas_squared", &mean::_sum_of_deltas_squared)
 
         .def_property_readonly("variance", &mean::variance)
 
@@ -311,11 +311,11 @@ void register_accumulators(py::module& accumulators) {
                      return self.count;
                  else if(key.equal(py::str("value")))
                      return self.value;
-                 else if(key.equal(py::str("sum_of_deltas_squared")))
-                     return self.sum_of_deltas_squared;
+                 else if(key.equal(py::str("_sum_of_deltas_squared")))
+                     return self._sum_of_deltas_squared;
                  else
                      throw py::key_error(
-                         py::str("{0} not one of count, value, sum_of_deltas_squared")
+                         py::str("{0} not one of count, value, _sum_of_deltas_squared")
                              .format(key));
              })
         .def("__setitem__",
@@ -324,17 +324,17 @@ void register_accumulators(py::module& accumulators) {
                      self.count = value;
                  else if(key.equal(py::str("value")))
                      self.value = value;
-                 else if(key.equal(py::str("sum_of_deltas_squared")))
-                     self.sum_of_deltas_squared = value;
+                 else if(key.equal(py::str("_sum_of_deltas_squared")))
+                     self._sum_of_deltas_squared = value;
                  else
                      throw py::key_error(
-                         py::str("{0} not one of count, value, sum_of_deltas_squared")
+                         py::str("{0} not one of count, value, _sum_of_deltas_squared")
                              .format(key));
              })
 
         .def("_ipython_key_completions_",
              [](py::object /* self */) {
-                 return py::make_tuple("count", "value", "sum_of_deltas_squared");
+                 return py::make_tuple("count", "value", "_sum_of_deltas_squared");
              })
 
         ;

tests/test_storage.py

@@ -98,7 +98,7 @@ def test_setting_profile():
 
     assert b["value"][0] == h[0].value
     assert b["count"][0] == h[0].count
-    assert b["sum_of_deltas_squared"][0] == h[0].sum_of_deltas_squared
+    assert b["_sum_of_deltas_squared"][0] == h[0]._sum_of_deltas_squared
 
     h[0] = bh.accumulators.Mean(count=6, value=3, variance=2)
     assert h[0].count == 6
@@ -109,20 +109,20 @@ def test_setting_profile():
 
     assert b["value"][0] == h[0].value
     assert b["count"][0] == h[0].count
-    assert b["sum_of_deltas_squared"][0] == h[0].sum_of_deltas_squared
+    assert b["_sum_of_deltas_squared"][0] == h[0]._sum_of_deltas_squared
 
     assert b[0]["value"] == a[0]["value"]
     assert b[0]["count"] == a[0]["count"]
-    assert b[0]["sum_of_deltas_squared"] == a[0]["sum_of_deltas_squared"]
+    assert b[0]["_sum_of_deltas_squared"] == a[0]["_sum_of_deltas_squared"]
 
     assert b[0]["value"] == a["value"][0]
     assert b[0]["count"] == a["count"][0]
-    assert b[0]["sum_of_deltas_squared"] == a["sum_of_deltas_squared"][0]
+    assert b[0]["_sum_of_deltas_squared"] == a["_sum_of_deltas_squared"][0]
 
     assert_array_equal(a.view().value, b.view()["value"])
     assert_array_equal(a.view().count, b.view()["count"])
     assert_array_equal(
-        a.view().sum_of_deltas_squared, b.view()["sum_of_deltas_squared"]
+        a.view()._sum_of_deltas_squared, b.view()["_sum_of_deltas_squared"]
     )