<｜begin▁of▁sentence｜>### Instruction:
As a network analyst specializing in political affiliations, imagine you're tasked with understanding the underlying community structure within a network of books on US politics. Picture yourself at a research institute focused on political discourse. Your colleague hands you a dataset stored in a file named "polbooks.gml," which contains information about connections between various political books. You've recently learned about a powerful tool called the EM algorithm available in a library called cdlib. This algorithm can help uncover hidden communities within networks. Your task is to utilize the EM algorithm from the cdlib library to detect communities within this network. Specifically, you're asked to identify three distinct communities. Once you've conducted the community detection, you're requested to generate and display a JSON representation of the resulting NodeClustering object, capturing the detected communities and their respective nodes.
### Response:
import networkx as nx
from cdlib import algorithms

# Reading the graph from polbooks dataset
G = nx.read_gml('polbooks.gml')

# Running EM algorithm with a predefined number of communities (k=3)
communities = algorithms.em(G, k=3)

# Generating a JSON representation of the NodeClustering object
communities_json = communities.to_json()
print(communities_json)
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