Add line_annate gist

line_annotation.py

@@ -0,0 +1,122 @@
+"""
+from  https://gist.github.com/coroa/cdcdb1ec1c73d4f6588501e2f7f46c45
+MIT License
+"""
+
+
+import numpy as np
+from matplotlib.text import Annotation
+from matplotlib.transforms import Affine2D
+
+
+class LineAnnotation(Annotation):
+    """A sloped annotation to *line* at position *x* with *text*
+    Optionally an arrow pointing from the text to the graph at *x* can be drawn.
+    Usage
+    -----
+    fig, ax = subplots()
+    x = linspace(0, 2*pi)
+    line, = ax.plot(x, sin(x))
+    ax.add_artist(LineAnnotation("text", line, 1.5))
+    """
+
+    def __init__(
+        self, text, line, x, xytext=(0, 5), textcoords="offset points", **kwargs
+    ):
+        """Annotate the point at *x* of the graph *line* with text *text*.
+
+        By default, the text is displayed with the same rotation as the slope of the
+        graph at a relative position *xytext* above it (perpendicularly above).
+
+        An arrow pointing from the text to the annotated point *xy* can
+        be added by defining *arrowprops*.
+
+        Parameters
+        ----------
+        text : str
+            The text of the annotation.
+        line : Line2D
+            Matplotlib line object to annotate
+        x : float
+            The point *x* to annotate. y is calculated from the points on the line.
+        xytext : (float, float), default: (0, 5)
+            The position *(x, y)* relative to the point *x* on the *line* to place the
+            text at. The coordinate system is determined by *textcoords*.
+        **kwargs
+            Additional keyword arguments are passed on to `Annotation`.
+
+        See also
+        --------
+        `Annotation`
+        `line_annotate`
+        """
+        assert textcoords.startswith(
+            "offset "
+        ), "*textcoords* must be 'offset points' or 'offset pixels'"
+
+        self.line = line
+        self.xytext = xytext
+
+        # Determine points of line immediately to the left and right of x
+        xs, ys = line.get_data()
+
+        def neighbours(x, xs, ys, try_invert=True):
+            (inds,) = np.where((xs <= x)[:-1] & (xs > x)[1:])
+            if len(inds) == 0:
+                assert try_invert, "line must cross x"
+                return neighbours(x, xs[::-1], ys[::-1], try_invert=False)
+
+            i = inds[0]
+            return np.asarray([(xs[i], ys[i]), (xs[i + 1], ys[i + 1])])
+
+        self.neighbours = n1, n2 = neighbours(x, xs, ys)
+
+        # Calculate y by interpolating neighbouring points
+        y = n1[1] + ((x - n1[0]) * (n2[1] - n1[1]) / (n2[0] - n1[0]))
+
+        kwargs = {
+            "horizontalalignment": "center",
+            "rotation_mode": "anchor",
+            **kwargs,
+        }
+        super().__init__(text, (x, y), xytext=xytext, textcoords=textcoords, **kwargs)
+
+    def get_rotation(self):
+        """Determines angle of the slope of the neighbours in display coordinate system"""
+        transData = self.line.get_transform()
+        dx, dy = np.diff(transData.transform(self.neighbours), axis=0).squeeze()
+        return np.rad2deg(np.arctan2(dy, dx))
+
+    def update_positions(self, renderer):
+        """Updates relative position of annotation text
+        Note
+        ----
+        Called during annotation `draw` call
+        """
+        xytext = Affine2D().rotate_deg(self.get_rotation()).transform(self.xytext)
+        self.set_position(xytext)
+        super().update_positions(renderer)
+
+
+def line_annotate(text, line, x, *args, **kwargs):
+    """Add a sloped annotation to *line* at position *x* with *text*
+
+    Optionally an arrow pointing from the text to the graph at *x* can be drawn.
+
+    Usage
+    -----
+    x = linspace(0, 2*pi)
+    line, = ax.plot(x, sin(x))
+    line_annotate("sin(x)", line, 1.5)
+
+    See also
+    --------
+    `LineAnnotation`
+    `plt.annotate`
+    """
+    ax = line.axes
+    a = LineAnnotation(text, line, x, *args, **kwargs)
+    if "clip_on" in kwargs:
+        a.set_clip_path(ax.patch)
+    ax.add_artist(a)
+    return a