From dd67b3fce7eacdc8f97cb7dfa9c7fd51a2b00214 Mon Sep 17 00:00:00 2001
From: Vighnesh Birodkar <vighneshbirodkar@gmail.com>
Date: Sat, 28 Jun 2014 11:06:30 +0530
Subject: [PATCH] Changed max_edge in example/plot_rag.py

---
 doc/examples/plot_rag.py        | 24 ++++++------------------
 skimage/graph/rag.py            |  2 +-
 skimage/graph/tests/test_rag.py |  4 ++++
 3 files changed, 11 insertions(+), 19 deletions(-)

diff --git a/doc/examples/plot_rag.py b/doc/examples/plot_rag.py
index d0ed3089..203f9454 100644
--- a/doc/examples/plot_rag.py
+++ b/doc/examples/plot_rag.py
@@ -9,32 +9,20 @@ weight of all the edges incident on it can be updated by a user defined
 function `weight_func`.
 
 The default behaviour is to use the smaller edge weight incase of a conflict.
-THe example below also shows how to use a custom function to take the larger
+The example below also shows how to use a custom function to take the larger
 weight instead.
 
 """
 from skimage.graph import rag
 import networkx as nx
 from matplotlib import pyplot as plt
+import numpy as np
 
 
-def max_edge(g, src, dst, neighbor):
-    try:
-        w1 = g.edge[src][neighbor]['weight']
-    except KeyError:
-        w1 = None
-
-    try:
-        w2 = g.edge[dst][neighbor]['weight']
-    except KeyError:
-        w2 = None
-
-    if w1 is None:
-        return w2
-    elif w2 is None:
-        return w1
-    else:
-        return max(w1, w2)
+def max_edge(g, src, dst, n):
+    w1 = g[n].get(src, {'weight': -np.inf})['weight']
+    w2 = g[n].get(dst, {'weight': -np.inf})['weight']
+    return max(w1, w2)
 
 
 def display(g, title):
diff --git a/skimage/graph/rag.py b/skimage/graph/rag.py
index 9150bfc4..69eed104 100644
--- a/skimage/graph/rag.py
+++ b/skimage/graph/rag.py
@@ -17,7 +17,7 @@ def min_weight(g, src, dst, n):
     src, dst : int
         The verices in `g` to be merged.
     n : int
-        A neighbor of `src` or `dst` or both
+        A neighbor of `src` or `dst` or both.
 
     Returns
     -------
diff --git a/skimage/graph/tests/test_rag.py b/skimage/graph/tests/test_rag.py
index 8179b92f..37c31887 100644
--- a/skimage/graph/tests/test_rag.py
+++ b/skimage/graph/tests/test_rag.py
@@ -23,10 +23,14 @@ def test_rag_merge():
 
     gc = g.copy()
 
+    # We merge nodes and ensure that the minimum weight is chosen
+    # when there is a conflict.
     g.merge_nodes(0, 2)
     assert g.edge[1][2]['weight'] == 10
     assert g.edge[2][3]['weight'] == 30
 
+    # We specify `max_edge` as `weight_func` as ensure that maximum
+    # weight is chosen in case on conflict
     gc.merge_nodes(0, 2, weight_func=max_edge)
     assert gc.edge[1][2]['weight'] == 20
     assert gc.edge[2][3]['weight'] == 40