Add residual plot overloading the - operator

src/plopp/backends/matplotlib/figure.py

@@ -44,3 +44,8 @@ def __truediv__(self, other):
         from .tiled import vstack
 
         return vstack(self, other)
+
+    def __sub__(self, other):
+        from .residuals import residuals
+
+        return residuals(self, other)

src/plopp/backends/matplotlib/residuals.py

@@ -0,0 +1,106 @@
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright (c) 2023 Scipp contributors (https://github.com/scipp)
+
+import matplotlib.pyplot as plt
+
+from ..protocols import FigureLike
+from .utils import copy_figure, make_figure
+
+
+class ResidualPlot:
+    def __init__(self, main_panel: FigureLike, res_panel: FigureLike):
+        self.main_panel = main_panel
+        self.res_panel = res_panel
+        self.panels = [self.main_panel, self.res_panel]
+
+    def __getitem__(self, key):
+        return self.panels[key]
+
+    def __repr__(self):
+        return f"ResidualPlot(main_panel={self.main_panel}, res_panel={self.res_panel})"
+
+    def _repr_mimebundle_(self, *args, **kwargs) -> dict:
+        return self.main_panel._repr_mimebundle_(*args, **kwargs)
+
+
+def residuals(main_fig: FigureLike, reference: FigureLike) -> ResidualPlot:
+    """
+    Create a residual plot from two figures, using the data from the second figure as
+    the reference the residuals are computed from.
+
+    Parameters
+    ----------
+    main_fig:
+        The main figure.
+    reference:
+        The reference figure.
+
+    Returns
+    -------
+    :
+        A figure with a main panel showing the data from both the main and reference
+        figures, and a smaller 'residuals' panel at the bottom displaying the difference
+        between the data from the main figure with the data from the reference figure.
+    """
+    # If there is a colormapper, we are dealing with a 2d figure
+    if hasattr(main_fig._view, 'colormapper') or hasattr(
+        reference._view, 'colormapper'
+    ):
+        raise TypeError("The residual plot only supports 1d figures.")
+    if len(reference.artists) != 1:
+        raise TypeError(
+            "The reference figure must contain exactly one line to "
+            "compute residuals."
+        )
+
+    fig = make_figure(figsize=(6.0, 4.0))
+    gs = fig.add_gridspec(
+        2,
+        1,
+        height_ratios=(4, 1),
+        hspace=0.0,
+    )
+
+    main_ax = fig.add_subplot(gs[0])
+    res_ax = fig.add_subplot(gs[1], sharex=main_ax)
+    main_panel = copy_figure(main_fig, ax=main_ax)
+    main_canvas = main_panel.canvas
+    if main_canvas.is_widget():
+        fig.canvas.toolbar_visible = False
+        fig.canvas.header_visible = False
+    ref_node = next(iter(reference.graph_nodes.values()))
+    data = ref_node()
+    if not data.name:
+        data.name = "reference"
+    ref_node.add_view(main_panel)
+    main_panel._view.render()
+    # main_view._view.artists[ref_node.id]._line.set_zorder(-10)
+    if main_canvas._legend:
+        main_ax.legend()
+    diff_nodes = [n - ref_node for n in main_fig.graph_nodes.values()]
+    res_panel = reference.__class__(reference._view.__class__, *diff_nodes, ax=res_ax)
+
+    main_ax.tick_params(
+        top=True, labeltop=True, bottom=False, labelbottom=False, direction='out'
+    )
+    main_ax.secondary_xaxis("bottom").tick_params(
+        axis="x",
+        direction="in",
+        top=False,
+        labeltop=False,
+        bottom=True,
+        labelbottom=False,
+    )
+    res_ax.tick_params(
+        top=False, labeltop=False, bottom=True, labelbottom=True, direction='out'
+    )
+    res_ax.secondary_xaxis("top").tick_params(
+        axis="x",
+        direction="in",
+        top=True,
+        labeltop=False,
+        bottom=False,
+        labelbottom=False,
+    )
+
+    return ResidualPlot(main_panel=main_panel, res_panel=res_panel)

src/plopp/data/factory.py

@@ -185,7 +185,9 @@ def scatter(npoints=500, scale=10.0, seed=1) -> sc.DataArray:
     )
 
 
-def random(shape, dtype='float64', unit='', dims=None, seed=None) -> sc.DataArray:
+def random(
+    shape, dtype='float64', unit='', dims=None, seed=None, binedges=False
+) -> sc.DataArray:
     """
     Generate a data array containing random data values.
 
@@ -213,7 +215,7 @@ def random(shape, dtype='float64', unit='', dims=None, seed=None) -> sc.DataArra
             dtype=dtype,
         ),
         coords={
-            dim: sc.arange(dim, shape[i], unit='m', dtype='float64')
+            dim: sc.arange(dim, shape[i] + int(binedges), unit='m', dtype='float64')
             for i, dim in enumerate(dims)
         },
     )

tests/backends/matplotlib/mpl_residuals_test.py

@@ -0,0 +1,101 @@
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright (c) 2023 Scipp contributors (https://github.com/scipp)
+
+import numpy as np
+import pytest
+
+import plopp as pp
+from plopp.backends.matplotlib.residuals import residuals
+from plopp.data.testing import data_array
+
+
+def test_single_line():
+    ref = data_array(ndim=1)
+    a = ref.copy()
+    a.values += np.random.uniform(-0.25, 0.25, size=len(a))
+    fig1 = ref.plot()
+    fig2 = a.plot()
+    fig = residuals(fig2, fig1)
+    assert len(fig.main_panel.fig.get_axes()) == 2
+    assert len(fig.main_panel.artists) == 2
+    assert len(fig.res_panel.artists) == 1
+
+
+def test_three_lines():
+    ref = data_array(ndim=1)
+    a = ref.copy()
+    a.values += np.random.uniform(-0.25, 0.25, size=len(a))
+    b = ref.copy()
+    b.values += np.random.uniform(-1.0, 1.0, size=len(b))
+    c = ref.copy()
+    fig1 = ref.plot()
+    fig2 = pp.plot({'a': a, 'b': b, 'c': c})
+    fig = residuals(fig2, fig1)
+    assert len(fig.main_panel.artists) == 4
+    assert len(fig.res_panel.artists) == 3
+
+
+def test_with_bin_edges():
+    ref = data_array(ndim=1, binedges=True)
+    a = ref.copy()
+    a.values += np.random.uniform(-0.25, 0.25, size=len(a))
+    fig1 = ref.plot()
+    fig2 = a.plot()
+    fig = residuals(fig2, fig1)
+    for artist in fig.main_panel.artists.values():
+        assert artist._line.get_linestyle() == '-'
+    for artist in fig.res_panel.artists.values():
+        assert artist._line.get_linestyle() == '-'
+
+
+def test_raises_when_given_2d_plots():
+    da1d = data_array(ndim=1)
+    da2d = data_array(ndim=2)
+    msg = "The residual plot only supports 1d figures."
+    with pytest.raises(TypeError, match=msg):
+        residuals(da2d.plot(), da1d.plot())
+    with pytest.raises(TypeError, match=msg):
+        residuals(da1d.plot(), da2d.plot())
+    with pytest.raises(TypeError, match=msg):
+        residuals(da2d.plot(), da2d.plot())
+
+
+def test_raises_when_reference_contains_multiple_lines():
+    ref = data_array(ndim=1)
+    a = ref.copy()
+    a.values += np.random.uniform(-0.25, 0.25, size=len(a))
+    b = ref.copy()
+    b.values += np.random.uniform(-1.0, 1.0, size=len(b))
+    fig1 = pp.plot({'a': a, 'b': b})
+    fig2 = ref.plot()
+    with pytest.raises(
+        TypeError,
+        match="The reference figure must contain exactly one line",
+    ):
+        residuals(fig2, fig1)
+
+
+def test_single_line_operator_minus():
+    ref = data_array(ndim=1)
+    a = ref.copy()
+    a.values += np.random.uniform(-0.25, 0.25, size=len(a))
+    fig1 = ref.plot()
+    fig2 = a.plot()
+    fig = fig2 - fig1
+    assert len(fig.main_panel.fig.get_axes()) == 2
+    assert len(fig.main_panel.artists) == 2
+    assert len(fig.res_panel.artists) == 1
+
+
+def test_three_lines_operator_minus():
+    ref = data_array(ndim=1)
+    a = ref.copy()
+    a.values += np.random.uniform(-0.25, 0.25, size=len(a))
+    b = ref.copy()
+    b.values += np.random.uniform(-1.0, 1.0, size=len(b))
+    c = ref.copy()
+    fig1 = ref.plot()
+    fig2 = pp.plot({'a': a, 'b': b, 'c': c})
+    fig = fig2 - fig1
+    assert len(fig.main_panel.artists) == 4
+    assert len(fig.res_panel.artists) == 3