Deleting a node and/or edge

[karthikcs]

I am working on a project based on Langgraph. I did not see an option to delete a node and/or an edge from an existing graph. I think we should have for complex projects where we need to serialize the graph and edit in the future

[akash97715]

its really needed any leads

[RayyanMasood]

So, this is really an open problem... What can be done currently? Treat it like a LinkedList of sorts? just skip the node? Or make the graph from scratch without the node?

[MacAttak]

Yes, this would be a great feature. I'll need this in an upcoming project. @karthikcs did you have any luck finding a solution?

[karthikcs]

Hi @MacAttak ,
I have achieved the expected result with following way.

def remove_node(self, node: str):
        try:
            assert node in self.get_node_names()   ## Make sure node is in the graph
        except AssertionError:
            self.logger.error(f"Node {node} not in graph}")
            raise AssertionError(f"Node {node} not in {self.get_node_names()}")
        
        ## Before popping the node, we need to remove the edges connected to it
        ## Get the edges connected to the node
        ## Update the edges only if they are not connected to the node. 

        
        self.workflow.edges = {edge for edge in self.workflow.edges if edge[0] != node and edge[1] != node}
        self.workflow.nodes.pop(node)
        self.logger.info(f"Node {node} removed from the graph along with its edges")
        return f"Node {node} removed from the graph along with its edges"

[KrishnanSG]

@karthikcs @MacAttak @akash97715
Hope this will help you guys. This is hack, I use in my projects whenever required.

TL;DR

Logic to remove the edge. It's internally stored as a set so you can simply run the remove method to knock it off.

print(graph.builder.edges)
# edges sorted as set internally 
# {('generate_structured_response', '__end__'), ('tools', 'agent'), ('__start__', 'agent')}

graph.builder.edges.remove((from, to)) # where from and to are the node names

Original Complied Graph

Modified Graph (before delete)

I'm adding a new_node after the generate_structured_response node.

modified_agent = agent.builder
modified_agent = modified_agent.add_node("new_node", func)
modified_agent = modified_agent.add_edge("generate_structured_response", "new_node")

Important

Both the generate_structured_response and new_node point to __end__, hence it's better to knock off (generate_structured_response, __end__)

Modified Graph (after delete)

modified_agent = agent.builder
modified_agent = modified_agent.add_node("new_node", func)
modified_agent = modified_agent.add_edge("generate_structured_response", "new_node")

# logic to remove the edge. It's internally sorted as a set so you can simply run the `remove` method to knock it off.
modified_agent.edges.remove(("generate_structured_response", "__end__"))

new_math_agent = new_math_agent.add_edge("new_node", "__end__")

agent.compile(name="agent")

[sainathpawar]

Lets say this is the issue and I want to remove node tool. so execute below steps.

1. First remove edges
   graph_builder.edges.remove(("tool","chatbot"))

2. remove a node
   graph_builder.nodes.pop("tool")

This will solve your problem.