[FIX] Allow both vmin and threshold argument values to be used in plotting functions using colorscale

doc/changes/latest.rst

@@ -34,6 +34,8 @@ Fixes
 
 - Fix ``fit_transform`` behavior to match when ``fit`` method is passed image data (:gh:`3897` by `Yasmin Mzayek`_)
 
+- Allow using both vmin and threshold with  "plotly" engine to be consistent with "matplotlib" behavior (:gh:`3945` by `Yasmin Mzayek`_)
+
 Enhancements
 ------------
 

nilearn/plotting/js_plotting_utils.py

@@ -80,11 +80,6 @@ def colorscale(cmap, values, threshold=None, symmetric_cmap=True,
     if symmetric_cmap and vmin is not None:
         warnings.warn('vmin cannot be chosen when cmap is symmetric')
         vmin = None
-    if threshold is not None:
-        if vmin is not None:
-            warnings.warn('choosing both vmin and a threshold is not allowed; '
-                          'setting vmin to 0')
-        vmin = 0
     if vmax is None:
         vmax = abs_values.max()
     # cast to float to avoid TypeError if vmax is a numpy boolean

nilearn/plotting/tests/test_js_plotting_utils.py

@@ -121,16 +121,13 @@ def test_colorscale_symmetric_cmap(vmin, vmax):
 
 
 @pytest.fixture
-def expected_vmin_vmax(values, vmax, vmin, threshold):
+def expected_vmin_vmax(values, vmax, vmin):
     """Returns expected vmin and vmax."""
-    if threshold is None:
-        if vmax is None:
-            return (min(values), max(values))
-        if min(values) < 0:
-            return (-vmax, vmax)
-        return (min(values), vmax) if vmin is None else (vmin, vmax)
-    else:
-        return (0, vmax)
+    if vmax is None:
+        return (min(values), max(values))
+    if min(values) < 0:
+        return (-vmax, vmax)
+    return (min(values), vmax) if vmin is None else (vmin, vmax)
 
 
 @pytest.mark.parametrize(

nilearn/plotting/tests/test_surf_plotting.py

@@ -811,6 +811,28 @@ def test_plot_surf_roi_error(engine):
         plot_surf_roi(mesh, roi_map=roi_idx, engine=engine)
 
 
+@pytest.mark.parametrize(
+    "kwargs", [{"vmin": 2}, {"vmin": 2, "threshold": 5}, {"threshold": 5}]
+)
+def test_plot_surf_roi_colorbar_vmin_equal_across_engines(kwargs):
+    """See issue https://github.com/nilearn/nilearn/issues/3944"""
+    if not PLOTLY_INSTALLED:
+        pytest.skip("Plotly is not installed; required for this test.")
+    mesh = generate_surf()
+    roi_map = np.arange(0, len(mesh[0]))
+
+    mpl_plot = plot_surf_roi(
+        mesh, roi_map=roi_map, colorbar=True, engine="matplotlib", **kwargs
+    )
+    plotly_plot = plot_surf_roi(
+        mesh, roi_map=roi_map, colorbar=True, engine="plotly", **kwargs
+    )
+    assert (
+        int(mpl_plot.axes[-1].get_yticklabels()[0].get_text())
+        == plotly_plot.figure.data[1]["cmin"]
+    )
+
+
 def test_plot_img_on_surf_hemispheres_and_orientations(img_3d_mni):
     nii = img_3d_mni
     # Check that all combinations of 1D or 2D hemis and orientations work.