Add viewport downsample algorithm

holoviews/operation/downsample.py

@@ -142,15 +142,19 @@ def _nth_point(x, y, n_out):
         y (np.ndarray): The y-values of the data.
         n_out (int): The number of output points.
     Returns:
-        np.array: The indexes of the selected datapoints.
+        slice: The slice of selected datapoints.
     """
     n_samples = len(x)
-    return np.arange(0, n_samples, max(1, math.ceil(n_samples / n_out)))
+    return slice(0, n_samples, max(1, math.ceil(n_samples / n_out)))
+
+def _viewport(x, y, n_out):
+    return slice(len(x))
 
 
 _ALGORITHMS = {
     'lttb': _lttb,
-    'nth': _nth_point
+    'nth': _nth_point,
+    'viewport': _viewport,
 }
 
 
@@ -164,9 +168,10 @@ class downsample1d(ResampleOperation1D):
         - `nth`: Selects every n-th point.
     """
 
-    algorithm = param.Selector(default='lttb', objects=['lttb', 'nth'])
+    algorithm = param.Selector(default='lttb', objects=list(_ALGORITHMS))
 
     def _process(self, element, key=None):
+        self.p.x_range = self.p.x_range or element.opts.get().kwargs.get("xlim")  # hack
         if isinstance(element, (Overlay, NdOverlay)):
             _process = partial(self._process, key=key)
             if isinstance(element, Overlay):
@@ -176,7 +181,9 @@ def _process(self, element, key=None):
             return element.clone(elements)
 
         if self.p.x_range:
-            element = element[slice(*self.p.x_range)]
+            xs = element.dimension_values(0)
+            x0, x1 = (np.argmin(np.abs(xs-coord)) for coord in self.p.x_range)
+            element = element.iloc[max(x0 - 1, 0):(x1 + 2)]
         if len(element) <= self.p.width:
             return element
         xs, ys = (element.dimension_values(i) for i in range(2))

holoviews/streams.py

@@ -1480,6 +1480,10 @@ class RangeX(LinkedStream):
     x_range = param.Tuple(default=None, length=2, constant=True, doc="""
       Range of the x-axis of a plot in data coordinates""")
 
+    def _set_stream_parameters(self, **kwargs):
+        kwargs.pop("y_range", None)
+        super()._set_stream_parameters(**kwargs)
+
 
 class RangeY(LinkedStream):
     """
@@ -1489,6 +1493,10 @@ class RangeY(LinkedStream):
     y_range = param.Tuple(default=None, length=2, constant=True, doc="""
       Range of the y-axis of a plot in data coordinates""")
 
+    def _set_stream_parameters(self, **kwargs):
+        kwargs.pop("x_range", None)
+        super()._set_stream_parameters(**kwargs)
+
 
 class BoundsXY(LinkedStream):
     """