When sparse matrices have explicit zero values, `axes.spy` plots those
zero values. This behavior seems unintentional. For example, the
following code should have a main diagonal with markers missing in the
middle, but `spy` currently plots a full main diagonal.
#~~~~~~~~~~~
import scipy.sparse as sparse
import matplotlib.pyplot as plt
sp = sparse.spdiags([[1,1,1,0,0,0,1,1,1]], [0], 9, 9)
plt.spy(sp, marker='.')
#~~~~~~~~~~~
Below is a patch which only plots the nonzero entries in a sparse
matrix. Note, sparse matrices with all zero entries raises an error;
this behavior differs from dense matrices. I could change this
behavior, but I wanted to minimize the code changed.
Cheers,
-Tony
PS: this patch also includes two trivial changes to some examples.
Index: lib/matplotlib/axes.py
===================================================================
--- lib/matplotlib/axes.py (revision 6122)
+++ lib/matplotlib/axes.py (working copy)
@@ -6723,9 +6723,11 @@
else:
if hasattr(Z, 'tocoo'):
c = Z.tocoo()
- y = c.row
- x = c.col
- z = c.data
+ nonzero = c.data != 0.
+ if all(nonzero == False):
+ raise ValueError('spy cannot plot sparse zeros
matrix')
+ y = c.row[nonzero]
+ x = c.col[nonzero]
else:
Z = np.asarray(Z)
if precision is None: mask = Z!=0.
Index: examples/pylab_examples/masked_demo.py
===================================================================
--- examples/pylab_examples/masked_demo.py (revision 6122)
+++ examples/pylab_examples/masked_demo.py (working copy)
@@ -1,4 +1,4 @@
-#!/bin/env python
+#!/usr/bin/env python
'''
Plot lines with points masked out.
Index: examples/misc/rec_groupby_demo.py
===================================================================
--- examples/misc/rec_groupby_demo.py (revision 6122)
+++ examples/misc/rec_groupby_demo.py (working copy)
@@ -2,7 +2,7 @@
import matplotlib.mlab as mlab
-r = mlab.csv2rec('data/aapl.csv')
+r = mlab.csv2rec('../data/aapl.csv')
r.sort()
def daily_return(prices):
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