| network.extraction {network} | R Documentation |
Various operators which allow extraction or replacement of various components of a network object.
## S3 method for class 'network': x[i, j, na.omit = FALSE] ## S3 method for class 'network': x[i, j, names.eval=NULL, add.edges=FALSE] <- value x %e% attrname x %e% attrname <- value x %eattr% attrname x %eattr% attrname <- value x %n% attrname x %n% attrname <- value x %nattr% attrname x %nattr% attrname <- value x %v% attrname x %v% attrname <- value x %vattr% attrname x %vattr% attrname <- value
x |
an object of class network. |
i, j |
indices of the vertices with respect to which adjacency is to be tested. Empty values indicate that all vertices should be employed (see below). |
na.omit |
logical; should missing edges be omitted (treated as no-adjacency), or should NAs be returned? (Default: return NA on missing.) |
names.eval |
optionally, the name of an edge attribute to use for assigning edge values. |
add.edges |
logical; should new edges be added to x where edges are absent and the appropriate element of value is non-zero? |
value |
the value (or set thereof) to be assigned to the selected element of x. |
attrname |
the name of a network or vertex attribute (as appropriate). |
Indexing for edge extraction operates in a manner analogous to matrix objects. Thus, x[,] selects all vertex pairs, x[1,-5] selects the pairing of vertex 1 with all vertices except for 5, etc. Following this, it is acceptable for i and/or j to be logical vectors indicating which vertices are to be included. During assignment, an attempt is made to match the elements of value to the extracted pairs in an intelligent way; in particular, elements of value will be replicated if too few are supplied (allowing expressions like x[1,]<-1). Where names.eval==NULL, zero and non-zero values are taken to indicate the presence of absence of edges. x[2,4]<-6 thus adds a single (2,4) edge to x, and x[2,4]<-0 removes such an edge (if present). If x is multiplex, assigning 0 to a vertex pair will eliminate all edges on that pair. Pairs are taken to be directed where is.directed(x)==TRUE, and undirected where is.directed(x)==FALSE.
If an edge attribute is specified using names.eval, then the provided values will be assigned to that attribute. When assigning values, only extant edges are employed (unless add.edges==TRUE); in the latter case, any non-zero assignment results in the addition of an edge where currently absent. If the attribute specified is not present on a given edge, it is added. Otherwise, any existing value is overwritten. The %e% operator can also be used to extract/assign edge values; in those roles, it is respectively equivalent to get.edge.value(x,attrname) and set.edge.value(x,attrname=attrname,value=value).
The %n% and %v% operators serve as front-ends to the network and vertex extraction/assignment functions (respectively). In the extraction case, x %n% attrname is equivalent to get.network.attribute(x,attrname), with x %v% attrname corresponding to get.vertex.attribute(x,attrname). In assignment, the respective equivalences are to set.network.attribute(x,attrname,value) and set.vertex.attribute(x,attrname,value).
The %eattr%, %nattr%, and %vattr% operators are equivalent to %e%, %n%, and %v% (respectively). The short forms are more succinct, but may produce less readable code.
The extracted data, or none.
Carter T. Butts buttsc@uci.edu
Butts, C. T. (2008). “network: a Package for Managing Relational Data in R.” Journal of Statistical Software, 24(2). http://www.jstatsoft.org/v24/i02/
is.adjacent, as.sociomatrix, attribute.methods, add.edges, network.operators
#Create a random graph (inefficiently) g<-network.initialize(10) g[,]<-matrix(rbinom(100,1,0.1),10,10) plot(g) #Demonstrate edge addition/deletion g[,]<-0 g[1,]<-1 g[2:3,6:7]<-1 g[,] #Set edge values g[,,names.eval="boo"]<-5 as.sociomatrix(g,"boo") g %e% "hoo" <- "wah" g %e% "hoo" #Set/retrieve network and vertex attributes g %n% "blah" <- "Pork!" #The other white meat? g %n% "blah" == "Pork!" #TRUE! g %v% "foo" <- letters[10:1] #Letter the vertices g %v% "foo" == letters[10:1] #All TRUE