test function for get_angle_index

src/diffpy/utils/diffraction_objects.py

@@ -248,15 +248,45 @@ def _set_array_from_range(self, begin, end, step_size=None, n_steps=None):
             array = np.linspace(begin, end, n_steps)
         return array
 
-    def get_angle_index(self, angle):
-        count = 0
-        for i, target in enumerate(self.angles):
-            if angle == target:
-                return i
-            else:
-                count += 1
-        if count >= len(self.angles):
-            raise IndexError(f"WARNING: no angle {angle} found in angles list")
+    def get_array_index(self, value, xtype=None):
+        """
+        returns the index of the closest value in the array associated with the specified xtype
+
+        Parameters
+        ----------
+        xtype str
+            the xtype used to access the array
+        value float
+            the target value to search for
+
+        Returns
+        -------
+        the index of the value in the array
+        """
+
+        if xtype is None:
+            xtype = self.input_xtype
+        if self.on_xtype(xtype) is None or len(self.on_xtype(xtype)[0]) == 0:
+            raise ValueError(
+                f"The '{xtype}' array is empty. " "Please ensure it is initialized and the correct xtype is used."
+            )
+        array = self.on_xtype(xtype)[0]
+        i = (np.abs(array - value)).argmin()
+        nearest_value = np.abs(array[i] - value)
+        distance = min(np.abs(value - array.min()), np.abs(value - array.max()))
+        threshold = 0.5 * (array.max() - array.min())
+
+        if nearest_value != 0 and (array.min() <= value <= array.max() or distance <= threshold):
+            warnings.warn(
+                f"WARNING: The value {value} is not an exact match of the '{xtype}' array. "
+                f"Returning the index of the closest value."
+            )
+        elif distance > threshold:
+            raise IndexError(
+                f"The value {value} is too far from any value in the '{xtype}' array. "
+                f"Please check if you have specified the correct xtype. "
+            )
+        return i
 
     def _set_xarrays(self, xarray, xtype):
         self.all_arrays = np.empty(shape=(len(xarray), 4))

tests/test_diffraction_objects.py

@@ -1,3 +1,4 @@
+import re
 from pathlib import Path
 
 import numpy as np
@@ -211,6 +212,67 @@ def _test_valid_diffraction_objects(actual_diffraction_object, function, expecte
     return np.allclose(actual_array, expected_array)
 
 
+params_index = [
+    # UC1: exact match
+    ([4 * np.pi, np.array([30.005, 60]), np.array([1, 2]), "tth", "tth", 30.005], [0]),
+    # UC2: target value lies in the array, returns the (first) closest index
+    ([4 * np.pi, np.array([30, 60]), np.array([1, 2]), "tth", "tth", 45], [0]),
+    ([4 * np.pi, np.array([30, 60]), np.array([1, 2]), "tth", "q", 0.25], [0]),
+    # UC3: target value out of the range but within reasonable distance, returns the closest index
+    ([4 * np.pi, np.array([0.25, 0.5, 0.71]), np.array([1, 2, 3]), "q", "q", 0.1], [0]),
+    ([4 * np.pi, np.array([30, 60]), np.array([1, 2]), "tth", "tth", 63], [1]),
+]
+
+
+@pytest.mark.parametrize("inputs, expected", params_index)
+def test_get_array_index(inputs, expected):
+    test = DiffractionObject(wavelength=inputs[0], xarray=inputs[1], yarray=inputs[2], xtype=inputs[3])
+    actual = test.get_array_index(value=inputs[5], xtype=inputs[4])
+    assert actual == expected[0]
+
+
+params_index_bad = [
+    # UC0: empty array
+    (
+        [2 * np.pi, np.array([]), np.array([]), "tth", "tth", 30],
+        [ValueError, "The 'tth' array is empty. Please ensure it is initialized and the correct xtype is used."],
+    ),
+    # UC1: empty array (because of invalid xtype)
+    (
+        [2 * np.pi, np.array([30, 60]), np.array([1, 2]), "tth", "invalid", 30],
+        [
+            ValueError,
+            "The 'invalid' array is empty. Please ensure it is initialized and the correct xtype is used.",
+        ],
+    ),
+    # UC3: value is too far from any element in the array
+    (
+        [2 * np.pi, np.array([30, 60, 90]), np.array([1, 2, 3]), "tth", "tth", 140],
+        [
+            IndexError,
+            "The value 140 is too far from any value in the 'tth' array. "
+            "Please check if you have specified the correct xtype.",
+        ],
+    ),
+    # UC4: value is too far from any element in the array (because of wrong xtype)
+    (
+        [2 * np.pi, np.array([30, 60, 90]), np.array([1, 2, 3]), "tth", "q", 30],
+        [
+            IndexError,
+            "The value 30 is too far from any value in the 'q' array. "
+            "Please check if you have specified the correct xtype.",
+        ],
+    ),
+]
+
+
+@pytest.mark.parametrize("inputs, expected", params_index_bad)
+def test_get_array_index_bad(inputs, expected):
+    test = DiffractionObject(wavelength=inputs[0], xarray=inputs[1], yarray=inputs[2], xtype=inputs[3])
+    with pytest.raises(expected[0], match=re.escape(expected[1])):
+        test.get_array_index(value=inputs[5], xtype=inputs[4])
+
+
 def test_dump(tmp_path, mocker):
     x, y = np.linspace(0, 5, 6), np.linspace(0, 5, 6)
     directory = Path(tmp_path)