network => igraph

Converting “network” objects to “igraph” is done by calling function asIgraph on a “network” object:

# check class of 'exNetwork'
class(exNetwork)

## [1] "network"

# convert to 'igraph'
g <- asIgraph(exNetwork)
# check class of the result
class(g)

## [1] "igraph"

Check if edgelists of the objects are identical

el.g <- get.edgelist(g)

## Warning: `get.edgelist()` was deprecated in igraph 2.0.0.
## ℹ Please use `as_edgelist()` instead.
## This warning is displayed once every 8 hours.
## Call `lifecycle::last_lifecycle_warnings()` to see where this warning was
## generated.

el.n <- as.matrix(exNetwork, "edgelist")
identical( as.numeric(el.g), as.numeric(el.n))

## [1] TRUE

igraph => network

Converting “igraph” objects to “network” is done by calling function asNetwork on an “igraph” object:

net <- asNetwork(exIgraph)

Note the warning because of a “non-standard” network attribute layout, which is a function. Printing “network” objects does not handle non-standard attributes very well. However, all the data and attributes are copied correctly.

Check if edgelists of the objects are identical

el.g2 <- get.edgelist(exIgraph)
el.n2 <- as.matrix(net, "edgelist")
identical( as.numeric(el.g2), as.numeric(el.n2))

## [1] TRUE

Handling attributes

Objects of class “igraph” and “network”, apart from storing actual network data (vertexes and edges), allow for adding attributes of vertexes, edges, and attributes of the network as a whole (called “network attributes” or “graph attributes” in the nomenclatures of packages “network” and “igraph” respectively).

Vertex and edge attributes are used by “igraph” and “network” in a largely similar fashion. However, network-level attributes are used differently. Objects of class “network” use network-level attributes to store various metadata, e.g., network size, whether the network is directed, is bipartite, etc. In “igraph” this information is stored separately.

The above difference affects the way the attributes are copied when we convert “network” and “igraph” objects into one another.

Both functions asNetwork and asIgraph have an additional argument attrmap that is used to specify how vertex, edge, and network attributes are copied. The attrmap argument requires a data frame. Rows of that data frame specify rules of copying/renaming different attributes. The data frame should have the following columns (all of class “character”):

• type: one of “network”, “vertex” or “edge”, whether the rule applies to network, vertex or edge attribute.
• fromslc: name of the which we are converting from
• fromattr: name of the attribute in the object we are converting from
• tocls: name of the class of the object we are converting to
• toattr: name of the attribute in the object we are converting to

The default rules are returned by a function attrmap(), these are:

attrmap()

##      type fromcls  fromattr   tocls       toattr
## 1 network network  directed  igraph         <NA>
## 2 network network bipartite  igraph         <NA>
## 3 network network     loops  igraph         <NA>
## 4 network network     mnext  igraph         <NA>
## 5 network network  multiple  igraph         <NA>
## 6 network network         n  igraph         <NA>
## 7 network network     hyper  igraph         <NA>
## 8  vertex  igraph      name network vertex.names

For example, the last row specifies a rule that when an object of class “igraph” is converted to class “network”, then a vertex attribute name in the “igraph” object will be copied to a vertex attribute called vertex.names in the resulting object of class “network.

If the column toattr contains an NA, that means that the corresponding attribute is not copied. For example, the first row specifies a rule that when an object of class “network” is converted to class “igraph”, then a network attribute directed in the “network” object is not copied to the resulting object of class “igraph”.

Users can customize the rules, or add new ones, by constructing similar data frames and supplying them through argument attrmap to functions asIgraph and asNetwork.

As an example let us set the option to always drop the na vertex attribute. First, we need to setup the rule by adding an extra row to the data frame returned by attrmap:

new_rule <- data.frame(type="vertex", fromcls="network", fromattr="na",
                       tocls="igraph", toattr=NA,
                       stringsAsFactors=FALSE)
# combine with the default rules
rules <- rbind( attrmap(), new_rule )
rules

##      type fromcls  fromattr   tocls       toattr
## 1 network network  directed  igraph         <NA>
## 2 network network bipartite  igraph         <NA>
## 3 network network     loops  igraph         <NA>
## 4 network network     mnext  igraph         <NA>
## 5 network network  multiple  igraph         <NA>
## 6 network network         n  igraph         <NA>
## 7 network network     hyper  igraph         <NA>
## 8  vertex  igraph      name network vertex.names
## 9  vertex network        na  igraph         <NA>

Now we can use it with asIgraph:

(ig1 <- asIgraph(exNetwork))

## IGRAPH 76a3dff D--- 15 11 -- 
## + attr: label (v/c), na (v/l), vertex.names (v/c), label (e/c), na
## | (e/l)
## + edges from 76a3dff:
##  [1]  2-> 1  3-> 1  4-> 1  5-> 1  6-> 7  8-> 9 10->11 11->12 14->12 12->13
## [11] 13->14

(ig2 <- asIgraph(exNetwork, amap=rules))

## IGRAPH cbb331f D--- 15 11 -- 
## + attr: label (v/c), vertex.names (v/c), label (e/c), na (e/l)
## + edges from cbb331f:
##  [1]  2-> 1  3-> 1  4-> 1  5-> 1  6-> 7  8-> 9 10->11 11->12 14->12 12->13
## [11] 13->14

# check if "na" was dropped
"na" %in% igraph::vertex_attr_names(ig1)

## [1] TRUE

"na" %in% igraph::vertex_attr_names(ig2)

## [1] FALSE

Example networks

Package intergraph contains four example networks:

• Objects exNetwork and exIgraph contain the same directed network as objects of class “network” and “igraph” respectively.
• Objects exNetwork2 and exIgraph2 contain the same undirected network as objects of class “network” and “igraph” respectively.

All four datasets contain:

• A vertex attribute label with vertex labels. These are letters from a to o.
• An edge attribute label with edge labels. These are pasted letters of the adjecent nodes.

We will use them in the examples below.

Networks are shown below using the following code:

layout(matrix(1:4, 2, 2, byrow=TRUE))
op <- par(mar=c(1,1,2,1))
# compute layout
coords <- layout.fruchterman.reingold(exIgraph)
plot(exIgraph, main="exIgraph", layout=coords)
plot(exIgraph2, main="exIgraph2", layout=coords)
plot(exNetwork, main="exNetwork", displaylabels=TRUE, coord=coords)
plot(exNetwork2, main="exNetwork2", displaylabels=TRUE, coord=coords)
par(op)

## Warning: `layout.fruchterman.reingold()` was deprecated in igraph 2.1.0.
## ℹ Please use `layout_with_fr()` instead.
## This warning is displayed once every 8 hours.
## Call `lifecycle::last_lifecycle_warnings()` to see where this warning was
## generated.

Session information

sessionInfo()

## R version 4.4.2 (2024-10-31)
## Platform: x86_64-pc-linux-gnu
## Running under: Ubuntu 24.04.1 LTS
## 
## Matrix products: default
## BLAS:   /usr/lib/x86_64-linux-gnu/openblas-pthread/libblas.so.3 
## LAPACK: /usr/lib/x86_64-linux-gnu/openblas-pthread/libopenblasp-r0.3.26.so;  LAPACK version 3.12.0
## 
## locale:
##  [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
##  [3] LC_TIME=en_US.UTF-8        LC_COLLATE=C              
##  [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
##  [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
##  [9] LC_ADDRESS=C               LC_TELEPHONE=C            
## [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       
## 
## time zone: Etc/UTC
## tzcode source: system (glibc)
## 
## attached base packages:
## [1] stats     graphics  grDevices utils     datasets  methods   base     
## 
## other attached packages:
## [1] igraph_2.1.1     network_1.18.2   knitr_1.49       intergraph_2.0-5
## [5] rmarkdown_2.29  
## 
## loaded via a namespace (and not attached):
##  [1] crayon_1.5.3          vctrs_0.6.5           cli_3.6.3            
##  [4] rlang_1.1.4           xfun_0.49             jsonlite_1.8.9       
##  [7] glue_1.8.0            buildtools_1.0.0      htmltools_0.5.8.1    
## [10] maketools_1.3.1       sys_3.4.3             sass_0.4.9           
## [13] fansi_1.0.6           grid_4.4.2            evaluate_1.0.1       
## [16] jquerylib_0.1.4       tibble_3.2.1          fastmap_1.2.0        
## [19] yaml_2.3.10           lifecycle_1.0.4       compiler_4.4.2       
## [22] coda_0.19-4.1         pkgconfig_2.0.3       statnet.common_4.10.0
## [25] lattice_0.22-6        digest_0.6.37         R6_2.5.1             
## [28] utf8_1.2.4            pillar_1.9.0          magrittr_2.0.3       
## [31] bslib_0.8.0           tools_4.4.2           cachem_1.1.0