Getting / Setting data on graph elements

Tulip allows to associate different kind of data to the graph elements. These data are stored in a structure called “property” which can be seen as an array indexed by the nodes and edges of a graph. The class tlp.PropertyInterface is the base interface for each graph property object. For each data type that can be attached to graph elements, there is a specific property class. Below is an exhaustive list of these classes:

• tlp.BooleanProperty : associate boolean values to nodes and edges
• tlp.ColorProperty : associate colors (r,g,b,a) to nodes and edges
• tlp.DoubleProperty: associate floating point values to nodes and edges
• tlp.IntegerProperty: associate integer values to nodes and edges
• tlp.LayoutProperty: associate positions (x,y,z) to nodes and bends/control points to edges
• tlp.SizeProperty: associate sizes (width,height,depth) to nodes and edges
• tlp.StringProperty: associate string values to nodes and edges

Lists of values can also be associated to graph elements through the use of the vector property classes listed below :

• tlp.BooleanVectorProperty : associate lists of boolean values to nodes and edges
• tlp.ColorVectorProperty : associate lists of colors (r,g,b,a) to nodes and edges
• tlp.DoubleVectorProperty: associate lists of floating point values to nodes and edges
• tlp.IntegerVectorProperty: associate lists of integer values to nodes and edges
• tlp.CoordVectorProperty: associate lists of positions (x,y,z) to nodes and to edges
• tlp.SizeVectorProperty: associate lists of sizes (width,height,depth) to nodes and edges
• tlp.StringVectorProperty: associate lists of string values to nodes and edges

In Tulip, there is two different kinds of graph properties :

• Local property : means that the property belongs to the graph. Its ancestors in the subgraph hierarchy do not have access to it but its descendants do.
• Inherited property : means that the property is inherited from an ancestor in the subgraph hierarchy. Only the graph whose the property is local can delete it.

Creating / Accessing / Deleting a graph property

Before using a graph property, you have to create it. To do so, use specific methods from the tlp.Graph class like tlp.Graph.getDoubleProperty(), tlp.Graph.getLayoutProperty(), tlp.Graph.getIntegerVectorProperty(), … (see Access and compute graph properties). All these methods take a string identifier as parameter to name the property. The created property can then be accessed / deleted through its identifier. It is also possible to create anonymous properties that won’t be managed by a graph. Below is some code samples that illustrate these features:

# create a DoubleProperty called "myMetric" if it does not exist
# otherwise return the already created property
myMetric = graph.getDoubleProperty("myMetric")

# Once created, a property can also be accessed through this syntax
myMetric = graph["myMetric"]

# The property can be deleted by the graph that has created it
graph.delLocalProperty("myMetric")

# Anonymous properties can also be instantiated the following way
myOtherMetric = tlp.DoubleProperty(graph)

Working with graph properties

The sample code below illustrate how to set / get data on graph elements through the use of a graph property:

# creating an integer property called "degree"
degree = graph.getIntegerProperty("degree")

# creating a boolean property called "loop"
loop = graph.getBooleanProperty("loop")

# filling the properties
for n in graph.getNodes():
  degree.setNodeValue(n, graph.deg(n))
  # the syntax below can also be used
  # degree[n] = graph.deg(n)

for e in graph.getEdges():
  loop.setEdgeValue(e, graph.source(e) == graph.target(e))
  # the syntax below can also be used
  # loop[e] = (graph.source(e) == graph.target(e))

# reading the properties
for n in graph.getNodes():
  d = degree.getNodeValue(n)
  # the syntax below can also be used
  # d = degree[n]
  print "degree of ", n, " = ", d

for e in graph.getEdges():
  isLoop = loop.getEdgeValue(e)
  # the syntax below can also be used
  # isLoop = loop[e]
  if isLoop:
    print e, " is a loop"