igraph for R: R interface of the igraph library for graph theory and network analysis

The internal format of graph objects has changed in a mostly backward-compatible way, to prepare for upgrading the C core to 0.10. Details are described at https://github.com/igraph/rigraph/wiki/The-igraph-object-format. Accessing graph objects that have been created with an older igraph version give a clean error message with instructions (#832). The new format cannot be read by igraph 1.4.3 or older, the following error is raised when trying to do so:

This graph was created by an old(er) igraph version.
  Call upgrade_graph() on it to use with the current igraph version
  For now we convert it on the fly...
Error in is_directed(object) : 
  REAL() can only be applied to a 'numeric', not a 'NULL'

The only supported remedy is to upgrade the igraph package to version 1.5.0 or later.

graph_version() now returns an integer scalar (#832, #847), 4 as of igraph 1.5.0 (#835).

• Vertex and edge sequences are converted to numeric vectors when used in attributes (#808).

• New largest_component() returns the largest connected component (#786, @ngmaclaren).

• Fix error message in make_graph() when simplify = ... is used with a non-formula (#834).

• Add more tests for graph_from_literal() (#826).

• Reenable serialization test and tests for dyad_census(), stabilize tests (#809, #822, #823).

• The documentation for the R package is now hosted at https://r.igraph.org/ (#780).

• Update vignette("installation-troubleshooting").

• Fix use of deprecated functions in examples, e.g., replace gsize() by ecount() (#827).

• Fix typos in ?eigen_centrality docs (@JJ).

• Update CONTRIBUTING.md and ORCID information (#791, #774).

• Add DOI to CITATION (#773).

• Add data for old igraph versions as constructed objects, and tests (#838).

• Ensure we're always using named indexes to access the internal data structure (#784).

• Prepare migration to igraph/C 0.10 (#781).

• Update generated interface (#765).