app.py

import streamlit as st
import matplotlib.pyplot as plt
import networkx as nx

# Sidebar for selecting an option
sidebar_option = st.sidebar.radio("Select an option", 
                                 ["Select an option", "Basic: Properties", 
                                  "Basic: Read and write graphs", "Basic: Simple graph"])

# Function to display properties and graph for Basic: Properties
def display_graph_properties(G):
    # Initialize a list for path lengths
    pathlengths = []

    # Display the source-target shortest path lengths
    st.write("### Source vertex {target:length, }")
    for v in G.nodes():
        spl = dict(nx.single_source_shortest_path_length(G, v))
        st.write(f"Vertex {v}: {spl}")
        for p in spl:
            pathlengths.append(spl[p])

    # Calculate and display the average shortest path length
    avg_path_length = sum(pathlengths) / len(pathlengths)
    st.write(f"### Average shortest path length: {avg_path_length}")

    # Calculate and display the distribution of path lengths
    dist = {}
    for p in pathlengths:
        if p in dist:
            dist[p] += 1
        else:
            dist[p] = 1

    st.write("### Length #paths")
    for d in sorted(dist.keys()):
        st.write(f"Length {d}: {dist[d]} paths")

    # Display the graph metrics with a "Properties" heading
    st.write("### Properties")
    st.write(f"Radius: {nx.radius(G)}")
    st.write(f"Diameter: {nx.diameter(G)}")
    st.write(f"Eccentricity: {nx.eccentricity(G)}")
    st.write(f"Center: {nx.center(G)}")
    st.write(f"Periphery: {nx.periphery(G)}")
    st.write(f"Density: {nx.density(G)}")

    # Visualize the graph
    st.write("### Graph Visualization")
    pos = nx.spring_layout(G, seed=3068)  # Seed layout for reproducibility
    plt.figure(figsize=(8, 6))
    nx.draw(G, pos=pos, with_labels=True, node_color='lightblue', node_size=500, font_size=10, font_weight='bold')
    st.pyplot(plt)

# Function to display graph for Basic: Read and write graphs
def display_read_write_graph(G):
    # Print the adjacency list of the graph
    st.write("### Adjacency List:")
    for line in nx.generate_adjlist(G):
        st.write(line)
    
    # Write the graph's edge list to a file
    st.write("### Writing Edge List to 'grid.edgelist' file:")
    nx.write_edgelist(G, path="grid.edgelist", delimiter=":")
    st.write("Edge list written to 'grid.edgelist'")

    # Read the graph from the edge list
    st.write("### Reading Edge List from 'grid.edgelist' file:")
    H = nx.read_edgelist(path="grid.edgelist", delimiter=":")
    st.write("Edge list read into graph H")

    # Visualize the graph
    st.write("### Graph Visualization:")
    pos = nx.spring_layout(H, seed=200)  # Seed for reproducibility
    plt.figure(figsize=(8, 6))
    nx.draw(H, pos, with_labels=True, node_color='lightblue', node_size=500, font_size=10, font_weight='bold')
    st.pyplot(plt)

# Function to display Simple Graphs for Basic: Simple graph
def display_simple_graph(G, pos=None):
    options = {
        "font_size": 36,
        "node_size": 3000,
        "node_color": "white",
        "edgecolors": "black",
        "linewidths": 5,
        "width": 5,
    }
    
    # Draw the network
    nx.draw_networkx(G, pos, **options)

    # Set margins for the axes so that nodes aren't clipped
    ax = plt.gca()
    ax.margins(0.20)
    plt.axis("off")
    st.pyplot(plt)

# Display Basic: Properties if selected
if sidebar_option == "Basic: Properties":
    st.title("Basic: Properties")
    option = st.radio("Choose a graph type:", ("Default Example", "Create your own"))

    # Default example: 5x5 grid graph
    if option == "Default Example":
        G = nx.lollipop_graph(4, 6)
        display_graph_properties(G)

    # Create your own graph
    elif option == "Create your own":
        num_nodes = st.number_input("Number of nodes:", min_value=2, max_value=50, value=5)
        num_edges = st.number_input("Number of edges per group (for lollipop graph):", min_value=1, max_value=10, value=3)

        # Button to generate the graph
        if st.button("Generate"):
            if num_nodes >= 2 and num_edges >= 1:
                G_custom = nx.lollipop_graph(num_nodes, num_edges)
                display_graph_properties(G_custom)

# Display Basic: Read and write graphs if selected
elif sidebar_option == "Basic: Read and write graphs":
    st.title("Basic: Read and write graphs")
    option = st.radio("Choose a graph type:", ("Default Example", "Create your own"))

    # Default example: 5x5 grid graph
    if option == "Default Example":
        G = nx.grid_2d_graph(5, 5)  # 5x5 grid
        display_read_write_graph(G)

    # Create your own graph
    elif option == "Create your own":
        rows = st.number_input("Number of rows:", min_value=2, max_value=20, value=5)
        cols = st.number_input("Number of columns:", min_value=2, max_value=20, value=5)

        # Button to generate the graph
        if st.button("Generate"):
            if rows >= 2 and cols >= 2:
                G_custom = nx.grid_2d_graph(rows, cols)
                display_read_write_graph(G_custom)

# Display Basic: Simple Graph if selected
elif sidebar_option == "Basic: Simple graph":
    st.title("Basic: Simple graph")
    option = st.radio("Choose a graph type:", ("Default Example", "Create your own"))

    # Default example: simple undirected graph
    if option == "Default Example":
        G = nx.Graph()
        G.add_edge(1, 2)
        G.add_edge(1, 3)
        G.add_edge(1, 5)
        G.add_edge(2, 3)
        G.add_edge(3, 4)
        G.add_edge(4, 5)

        # explicitly set positions for visualization
        pos = {1: (0, 0), 2: (-1, 0.3), 3: (2, 0.17), 4: (4, 0.255), 5: (5, 0.03)}
        display_simple_graph(G, pos)

    # Create your own graph
    elif option == "Create your own":
        num_nodes = st.number_input("Number of nodes:", min_value=2, max_value=20, value=5)
        edges = []
        
        # Let the user define edges
        st.write("Enter the edges (as pairs of nodes) separated by commas. For example, 1,2 or 3,4.")
        edge_input = st.text_area("Edges:", value="1,2\n1,3\n2,3")
        
        # Parse the edges
        if edge_input:
            edge_list = edge_input.split("\n")
            for edge in edge_list:
                u, v = map(int, edge.split(","))
                edges.append((u, v))

        # Button to generate the graph
        if st.button("Generate"):
            G_custom = nx.Graph()
            G_custom.add_edges_from(edges)
            
            # Set a basic layout (spring layout as default)
            pos = nx.spring_layout(G_custom, seed=42)
            display_simple_graph(G_custom, pos)