R/mb.R

In MXM: Feature Selection (Including Multiple Solutions) and Bayesian Networks

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##### Return and plot if requested the neighbours of an undirected graph
#####
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mb <- function(G, node) {
  ## G is the adjacency matrix of an UN-DIRECTED graph
  ## node is a number between 1 and the number of nodes
  ## it is a node whose neighbors you want to find
  ## it can also be a vector with more than one nodes
  
  if ( is.null( colnames(G) ) ) {
    p <- ncol(G)
    nama <- paste("X", 1:p, sep = "")
  } else  nama <- colnames(G)
  
  parents <- which( G[node, ] == 3 & t(G[node, ] != 2) )
  relatives <- which( ( G[node, ] == 1 & G[, node] == 1 ) )
  children <- which( G[node, ] == 2 )
  le <- length(children) 
  spouses <- list()
  if (le > 0) {
    for (i in children) {
      spousa <- which( G[i, ] == 3 )
      spouses[[ i ]] <- setdiff(spousa, node) 
    }
  }
  
  names(spouses) <- nama[ children ]
  spo <- unlist(spouses)
  blanket <- c(parents, children, spo, relatives)
  blanket <- unique(blanket)
  
  if ( length(blanket) == 0 ) {
  } else {  
    Grel <- G[c(node, blanket), c(node, blanket)]
    aa <- which(Grel == 1 & t(Grel) == 1, arr.ind = TRUE)
    Grel[aa] <- 2
    Grel[Grel != 2] <- 0
  }
  
  list( parents = parents, children = children, spouses = spouses, relatives = relatives, markov.blanket = blanket )
}