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 sub-graph hierarchy do not have access to it but its descendants do.
• Inherited property : means that the property is inherited from an ancestor in the sub-graph 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"