ENH: npv: Rework npv to mimic broadcasting behaviour

Author: Kai-Striega

benchmarks/benchmarks.py

@@ -5,15 +5,6 @@
 import numpy_financial as npf
 
 
-def _to_decimal_array_1d(array):
-    return np.array([Decimal(x) for x in array.tolist()])
-
-
-def _to_decimal_array_2d(array):
-    decimals = [Decimal(x) for row in array.tolist() for x in row]
-    return np.array(decimals).reshape(array.shape)
-
-
 class Npv2D:
 
     param_names = ["n_cashflows", "cashflow_lengths", "rates_lengths"]
@@ -24,26 +15,19 @@ class Npv2D:
     ]
 
     def __init__(self):
-        self.rates_decimal = None
         self.rates = None
-        self.cashflows_decimal = None
         self.cashflows = None
 
     def setup(self, n_cashflows, cashflow_lengths, rates_lengths):
         rng = np.random.default_rng(0)
         cf_shape = (n_cashflows, cashflow_lengths)
         self.cashflows = rng.standard_normal(cf_shape)
         self.rates = rng.standard_normal(rates_lengths)
-        self.cashflows_decimal = _to_decimal_array_2d(self.cashflows)
-        self.rates_decimal = _to_decimal_array_1d(self.rates)
 
     def time_for_loop(self, n_cashflows, cashflow_lengths, rates_lengths):
         for rate in self.rates:
             for cashflow in self.cashflows:
                 npf.npv(rate, cashflow)
 
-    def time_for_loop_decimal(self, n_cashflows, cashflow_lengths, rates_lengths):
-        for rate in self.rates_decimal:
-            for cashflow in self.cashflows_decimal:
-                npf.npv(rate, cashflow)
-
+    def time_broadcast(self, n_cashflows, cashflow_lengths, rates_lengths):
+        npf.npv(self.rates, self.cashflows)

numpy_financial/_financial.py

@@ -13,8 +13,10 @@
 
 from decimal import Decimal
 
+import numba as nb
 import numpy as np
 
+
 __all__ = ['fv', 'pmt', 'nper', 'ipmt', 'ppmt', 'pv', 'rate',
            'irr', 'npv', 'mirr',
            'NoRealSolutionError', 'IterationsExceededError']
@@ -35,6 +37,19 @@ class IterationsExceededError(Exception):
     """Maximum number of iterations reached."""
 
 
+def _get_output_array_shape(*arrays):
+    return tuple(array.shape[0] for array in arrays)
+
+
+def _ufunc_like(array):
+    try:
+        # If size of array is one, return scalar
+        return array.item()
+    except ValueError:
+        # Otherwise, return entire array
+        return array.squeeze()
+
+
 def _convert_when(when):
     # Test to see if when has already been converted to ndarray
     # This will happen if one function calls another, for example ppmt
@@ -825,6 +840,20 @@ def irr(values, *, guess=None, tol=1e-12, maxiter=100, raise_exceptions=False):
     return np.nan
 
 
+@nb.njit
+def _npv_native(rates, values, out):
+    for i in range(rates.shape[0]):
+        for j in range(values.shape[0]):
+            acc = 0.0
+            for t in range(values.shape[1]):
+                if rates[i] == -1.0:
+                    acc = np.nan
+                    break
+                else:
+                    acc += values[j, t] / ((1.0 + rates[i]) ** t)
+            out[i, j] = acc
+
+
 def npv(rate, values):
     r"""Return the NPV (Net Present Value) of a cash flow series.
 
@@ -892,16 +921,31 @@ def npv(rate, values):
     >>> np.round(npf.npv(rate, cashflows) + initial_cashflow, 5)
     3065.22267
 
+    The NPV calculation may be applied to several ``rates`` and ``cashflows``
+    simulatneously. This produces an array of shape ``(len(rates), len(cashflows))``.
+    >>> rates = [0.00, 0.05, 0.10]
+    >>> cashflows = [[-4_000, 500, 800], [-5_000, 600, 900]]
+    >>> npf.npv(rates, cashflows).round(2)
+    array([[-2700.  , -3500.  ],
+           [-2798.19, -3612.24],
+           [-2884.3 , -3710.74]])
+
     """
-    values = np.atleast_2d(values)
-    timestep_array = np.arange(0, values.shape[1])
-    npv = (values / (1 + rate) ** timestep_array).sum(axis=1)
-    try:
-        # If size of array is one, return scalar
-        return npv.item()
-    except ValueError:
-        # Otherwise, return entire array
-        return npv
+    values_inner = np.atleast_2d(values)
+    rate_inner = np.atleast_1d(rate)
+
+    if rate_inner.ndim != 1:
+        msg = "invalid shape for rates. Rate must be either a scalar or 1d array"
+        raise ValueError(msg)
+
+    if values_inner.ndim != 2:
+        msg = "invalid shape for values. Values must be either a 1d or 2d array"
+        raise ValueError(msg)
+
+    output_shape = _get_output_array_shape(rate_inner, values_inner)
+    out = np.empty(output_shape)
+    _npv_native(rate_inner, values_inner, out)
+    return _ufunc_like(out)
 
 
 def mirr(values, finance_rate, reinvest_rate, *, raise_exceptions=False):

pyproject.toml

@@ -39,9 +39,12 @@ packages = [{include = "numpy_financial"}]
 [tool.poetry.dependencies]
 python = "^3.10"
 numpy = "^1.23"
+numba = "^0.59.1"
 
 [tool.poetry.group.test.dependencies]
 pytest = "^8.0"
+hypothesis = {extras = ["numpy"], version = "^6.99.11"}
+pytest-xdist = {extras = ["psutil"], version = "^3.5.0"}
 
 
 [tool.poetry.group.docs.dependencies]

tests/test_financial.py

@@ -11,10 +11,45 @@
     assert_equal,
     assert_raises,
 )
+from hypothesis import given, settings
+import hypothesis.strategies as st
+import hypothesis.extra.numpy as npst
 
 import numpy_financial as npf
 
 
+def float_dtype():
+    return npst.floating_dtypes(sizes=[32, 64], endianness="<")
+
+
+def int_dtype():
+    return npst.integer_dtypes(sizes=[32, 64], endianness="<")
+
+
+def uint_dtype():
+    return npst.unsigned_integer_dtypes(sizes=[32, 64], endianness="<")
+
+
+real_scalar_dtypes = st.one_of(float_dtype(), int_dtype(), uint_dtype())
+
+
+cashflow_array_strategy = npst.arrays(
+    dtype=real_scalar_dtypes,
+    shape=npst.array_shapes(min_dims=1, max_dims=2, min_side=0, max_side=25),
+)
+cashflow_list_strategy = cashflow_array_strategy.map(lambda x: x.tolist())
+
+cashflow_array_like_strategy = st.one_of(
+    cashflow_array_strategy,
+    cashflow_list_strategy,
+)
+
+short_scalar_array = npst.arrays(
+    dtype=real_scalar_dtypes,
+    shape=npst.array_shapes(min_dims=0, max_dims=1, min_side=0, max_side=5),
+)
+
+
 def assert_decimal_close(actual, expected, tol=Decimal("1e-7")):
     # Check if both actual and expected are iterable (like arrays)
     if hasattr(actual, "__iter__") and hasattr(expected, "__iter__"):
@@ -244,11 +279,27 @@ def test_npv(self):
             rtol=1e-2,
         )
 
-    def test_npv_decimal(self):
-        assert_equal(
-            npf.npv(Decimal("0.05"), [-15000, 1500, 2500, 3500, 4500, 6000]),
-            Decimal("122.894854950942692161628715"),
-        )
+    @given(rates=short_scalar_array, values=cashflow_array_strategy)
+    @settings(deadline=None)
+    def test_fuzz(self, rates, values):
+        npf.npv(rates, values)
+
+    @pytest.mark.parametrize("rates", ([[1, 2, 3]], numpy.empty(shape=(1, 1, 1))))
+    def test_invalid_rates_shape(self, rates):
+        cashflows = [1, 2, 3]
+        with pytest.raises(ValueError):
+            npf.npv(rates, cashflows)
+
+    @pytest.mark.parametrize("cf", ([[[1, 2, 3]]], numpy.empty(shape=(1, 1, 1))))
+    def test_invalid_cashflows_shape(self, cf):
+        rates = [1, 2, 3]
+        with pytest.raises(ValueError):
+            npf.npv(rates, cf)
+
+    @pytest.mark.parametrize("rate", (-1, -1.0))
+    def test_rate_of_negative_one_returns_nan(self, rate):
+        cashflow = numpy.arange(5)
+        assert numpy.isnan(npf.npv(rate, cashflow))
 
 
 class TestPmt:
@@ -336,68 +387,6 @@ def test_mirr(self, values, finance_rate, reinvest_rate, expected):
         else:
             assert_(numpy.isnan(result))
 
-    @pytest.mark.parametrize("number_type", [Decimal, float])
-    @pytest.mark.parametrize(
-        "args, expected",
-        [
-            (
-                {
-                    "values": [
-                        "-4500",
-                        "-800",
-                        "800",
-                        "800",
-                        "600",
-                        "600",
-                        "800",
-                        "800",
-                        "700",
-                        "3000",
-                    ],
-                    "finance_rate": "0.08",
-                    "reinvest_rate": "0.055",
-                },
-                "0.066597175031553548874239618",
-            ),
-            (
-                {
-                    "values": ["-120000", "39000", "30000", "21000", "37000", "46000"],
-                    "finance_rate": "0.10",
-                    "reinvest_rate": "0.12",
-                },
-                "0.126094130365905145828421880",
-            ),
-            (
-                {
-                    "values": ["100", "200", "-50", "300", "-200"],
-                    "finance_rate": "0.05",
-                    "reinvest_rate": "0.06",
-                },
-                "0.342823387842176663647819868",
-            ),
-            (
-                {
-                    "values": ["39000", "30000", "21000", "37000", "46000"],
-                    "finance_rate": "0.10",
-                    "reinvest_rate": "0.12",
-                },
-                numpy.nan,
-            ),
-        ],
-    )
-    def test_mirr_decimal(self, number_type, args, expected):
-        values = [number_type(v) for v in args["values"]]
-        result = npf.mirr(
-            values,
-            number_type(args["finance_rate"]),
-            number_type(args["reinvest_rate"]),
-        )
-
-        if expected is not numpy.nan:
-            assert_decimal_close(result, number_type(expected), tol=1e-15)
-        else:
-            assert numpy.isnan(result)
-
     def test_mirr_no_real_solution_exception(self):
         # Test that if there is no solution because all the cashflows
         # have the same sign, then npf.mirr returns NoRealSolutionException