Output of igraph clustering functions-CodePudding

I constructed a graph from a data-frame using the igraph graph_from_data_frame function. My two first column represent the edge list, and i have another column named "weight". There is several other attributes columns.

I then tried to find a community structure within my graph using cluster_fast_greedy.

data <- data %>%  rename(weight = TH_LIEN_2)
graph <- graph_from_data_frame(data,directed=FALSE)
is_weighted(graph)


cluster_1 <- cluster_fast_greedy(graph, weights = NULL)

The output is a list of three (merges, modularity, membership), each containing some of my vertices. However, the following returns "NULL":


cluster_1[["merges"]]
cluster_1[["modularity"]]
cluster_1[["membership"]]

(I believe cluster_1[["membership"]] is supposed to be a list of integer indicating the cluster the vertices belong to?)

I have tried different method of clustering (cluster_fast_greedy, cluster_label_prop, cluster_leading_eigen, cluster_spinglass, cluster_walktrap) and with a weighted and non weighted graph and the output looks the same every time. (The number of element on the list varying from 1 to 4)

Does anyone have an idea of why it does that?

Thank you and have a nice day!

Cassandra

CodePudding user response：

You should use the dollar sign $ to access the cluster object. For example

g <- make_full_graph(5) %du% make_full_graph(5) %du% make_full_graph(5)
g <- add_edges(g, c(1, 6, 1, 11, 6, 11))
fc <- cluster_fast_greedy(g)

and you will see

> str(fc)
Class 'communities'  hidden list of 5
 $ merges    : num [1:14, 1:2] 3 4 5 1 12 13 15 11 7 8 ...
 $ modularity: num [1:15] -6.89e-02 -4.59e-02 6.94e-18 6.89e-02 1.46e-01 ...
 $ membership: num [1:15] 3 3 3 3 3 1 1 1 1 1 ...
 $ algorithm : chr "fast greedy"
 $ vcount    : int 15

> fc$merges
      [,1] [,2]
 [1,]    3    2
 [2,]    4   16
 [3,]    5   17
 [4,]    1   18
 [5,]   12   14
 [6,]   13   20
 [7,]   15   21
 [8,]   11   22
 [9,]    7    9
[10,]    8   24
[11,]   10   25
[12,]    6   26
[13,]   27   19
[14,]   23   28

> fc$modularity
 [1] -6.887052e-02 -4.591368e-02  6.938894e-18  6.887052e-02  1.460055e-01
 [6]  1.689624e-01  2.148760e-01  2.837466e-01  3.608815e-01  3.838384e-01
[11]  4.297521e-01  4.986226e-01  5.757576e-01  3.838384e-01 -1.110223e-16

> fc$membership
 [1] 3 3 3 3 3 1 1 1 1 1 2 2 2 2 2

> fc$algorithm
[1] "fast greedy"

> fc$vcount
[1] 15