IndexError in rdm_plot._contour_coords when contour mask touches matrix edges

[XuShaobo-py]

Describe the bug
When plotting an RDM with a contour mask that includes the outermost edges of the matrix (e.g., an all-True mask), the _contour_coords function throws an IndexError.

This occurs because the contour-drawing algorithm checks the state of neighboring cells to find boundaries, but it lacks boundary condition checks. When a mask cell is located at the absolute edge of the matrix, checking its outer neighbor results in an out-of-bounds index.

To Reproduce

import matplotlib.pyplot as plt
import numpy as np
from rsatoolbox.rdm.rdms import RDMs
from rsatoolbox.vis.rdm_plot import show_rdm, Symmetry

n_conditions = 9
n_utv = int(n_conditions * (n_conditions - 1) / 2)  

dissim_utv = np.random.rand(n_utv)
rdms = RDMs(
    dissimilarities=dissim_utv,
    dissimilarity_measure='random'
)

mask = np.ones(n_utv, dtype=bool)  # Masking all upper triangular values as True, including the edges

show_rdm(
    rdms,
    vmin=0,
    vmax=1,
    show_colorbar=None,
    contour=mask,
    contour_symmetry=Symmetry.UPPER
)
plt.show()

Versions

• rsatoolbox 0.3.2
• python 3.11

Fix
In line 410 of rsatoolbox.vis.rdm_plot.py, change this line:

if not mask_t[(x+neighbor[0], y+neighbor[1])]:

to

nx, ny = x + neighbor[0], y + neighbor[1]
if nx < 0 or ny < 0 or nx >= mask_t.shape[0] or ny >= mask_t.shape[1] or not mask_t[(nx, ny)]:

This will fix the bug and create a rdm plot as follows:

stack trace

Traceback (most recent call last):
  File "...\rsatoolbox\vis\rdm_plot.py", line 173, in _plot_multi_rdm
    handles[p]["image"] = _show_rdm_panel(conf.for_single(rdm_index), ax_array[r, c])
  File "...\rsatoolbox\vis\rdm_plot.py", line 322, in _show_rdm_panel
    _contour(conf, ax)
  File "...\rsatoolbox\vis\rdm_plot.py", line 360, in _contour
    for (x1, y1, x2, y2) in _contour_coords(conf.contour_mask, -0.5):
  File "...\rsatoolbox\vis\rdm_plot.py", line 410, in _contour_coords
    if not mask_t[(x+neighbor[0], y+neighbor[1])]:
IndexError: index 9 is out of bounds for axis 0 with size 9