matplotlib/matplotlib · error · ValueError

z array must have same length as triangulation x and y array

Error message

z array must have same length as triangulation x and y arrays

What it means

Error "z array must have same length as triangulation x and y arrays" thrown in matplotlib/matplotlib.

Source

Thrown at lib/matplotlib/tri/_tricontour.py:59

            self._mins = args[0]._mins
            self._maxs = args[0]._maxs
        else:
            from matplotlib import _tri
            tri, z = self._contour_args(args, kwargs)
            C = _tri.TriContourGenerator(tri.get_cpp_triangulation(), z)
            self._mins = [tri.x.min(), tri.y.min()]
            self._maxs = [tri.x.max(), tri.y.max()]

        self._contour_generator = C
        return kwargs

    def _contour_args(self, args, kwargs):
        tri, args, kwargs = Triangulation.get_from_args_and_kwargs(*args,
                                                                   **kwargs)
        z, *args = args
        z = np.ma.asarray(z)
        if z.shape != tri.x.shape:
            raise ValueError('z array must have same length as triangulation x'
                             ' and y arrays')

        # z values must be finite, only need to check points that are included
        # in the triangulation.
        z_check = z[np.unique(tri.get_masked_triangles())]
        if np.ma.is_masked(z_check):
            raise ValueError('z must not contain masked points within the '
                             'triangulation')
        if not np.isfinite(z_check).all():
            raise ValueError('z array must not contain non-finite values '
                             'within the triangulation')

        z = np.ma.masked_invalid(z, copy=False)
        self.zmax = float(z_check.max())
        self.zmin = float(z_check.min())
        if self.logscale and self.zmin <= 0:
            func = 'contourf' if self.filled else 'contour'
            raise ValueError(f'Cannot {func} log of negative values.')

View on GitHub (pinned to b379c1b69e)

When it happens

Trigger: Thrown at lib/matplotlib/tri/_tricontour.py:59 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of matplotlib/matplotlib@b379c1b69e (2026-08-21). Data as JSON: /api/errors/5f8e60afadadb8e2. Report an issue: GitHub.