def get_array_index(self, xtype, xvalue):
        """Return the index of the closest value in the array associated with
        the specified xtype and the value provided.
        ...
        """
        xtype = self._input_xtype
        xarray = self.on_xtype(xtype)[0]
        if len(xarray) == 0:
            raise ValueError(
                f"The '{xtype}' array is empty. "
                "Please ensure it is initialized."
            )
        index = (np.abs(xarray - xvalue)).argmin()
        return index

x = np.linspace(0, 90, 1000)
y = np.random.rand(1000)
tmp = DiffractionObject(
     xarray=x,
     yarray=y,
     xtype="angle",
     wavelength=1.54,
)
index_angle = tmp.get_array_index(xvalue=0.24, xtype="angle")
index_q_from_function = tmp.get_array_index(xvalue=0.24, xtype="q")
real_index_q =  np.argmin(np.abs(tmp.on_xtype("q")[0] - 0.24))
print(index_angle == index_q_from_function)
print(index_q_from_function == real_index_q)