improve warning message in sparse
@@ -543,8 +543,8 @@ class _compressed_sparse_matrix(sparse_data._data_matrix,
else:
warnings.warn('Changing the sparsity structure of a '
- '{}_matrix is expensive.'
- ' lil_matrix is more efficient.'.format(self.format))
+ '{}_matrix is expensive.'.format(self.format),
+ _base.SparseEfficiencyWarning)
# replace where possible
mask = offsets > -1
self.data[offsets[mask]] = x[mask]
