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FIX: Raise for single row/column grids with nearest shading · matplotlib/matplotlib@5f8c2f0 · GitHub
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FIX: Raise for single row/column grids with nearest shading
Explicitly providing a single row or single column grid for pcolor(mesh) with nearest shading, silently produces no plot. This happens because nearest shading interprets the X and Y coordinates as cell centers and then calculates, from neighboring centers, new X and Y coordinates for the cell corners. When a coordinate array contains only one center, its corresponding cell size cannot be determined from neighboring centers. This commit fixes the behavior of silently producing no plot by raising an error for such grids and recommending that users supply cell corners instead.
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2 files changed

Lines changed: 18 additions & 2 deletions

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‎lib/matplotlib/axes/_axes.py‎

Lines changed: 8 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -6560,8 +6560,14 @@ def _interp_grid(X, require_monotonicity=False):
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X[:, :-1] + dX,
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X[:, [-1]] + dX[:, [-1]]))
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else:
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# This is just degenerate, but we can't reliably guess
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# a dX if there is just one value.
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if require_monotonicity:
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# Coordinate array has a single cell center, so its
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# corresponding cell size cannot be determined
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# from neighboring centers.
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raise TypeError(f"Dimensions of X ({Nx}) and Y ({Ny}) "
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"must be greater than one when using "
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f"shading='nearest'. Supply explicit "
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f"cell edges to {funcname}.")
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X = np.hstack((X, X))
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return X
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‎lib/matplotlib/tests/test_axes.py‎

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Original file line numberDiff line numberDiff line change
@@ -1678,6 +1678,16 @@ def test_pcolorargs():
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# bad grid warnings.
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ax.pcolormesh(X+10*noise_X, Y+10*noise_Y, Z, shading='auto')
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assert len(record) == 2
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# Grid cannot contain a single row or single column for nearest shading.
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x = [1, 2, 3]
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y = [4]
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Z = np.arange(3).reshape(1, 3)
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with pytest.raises(TypeError):
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ax.pcolormesh(x, y, Z)
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with pytest.raises(TypeError):
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ax.pcolormesh(y, x, Z.T)
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with pytest.raises(TypeError):
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ax.pcolormesh(y, y, Z[:, [0]])
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def test_pcolormesh_underflow_error():

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