R/getChildren.R

In SWS-Methodology/faoswsUtil: A suite of function to support the FAO new Statistical Working System

##' Get Children
##' 
##' This function takes a commodity tree and a vector of node ids and returns a 
##' vector of these nodes as well as all the descendants (or ancestors) of these
##' nodes.
##' 
##' @param commodityTree A data.table with parent and child node IDs 
##'   (corresponding to the IDs in nodes) which specify the commodity tree 
##'   structure.
##' @param parentColname The column name of commodityTree which contains the ID 
##'   of the parent node.
##' @param childColname The column name of commodityTree which contains the ID 
##'   of the child node.
##' @param topNodes Vector containing the node names/ids for which the children 
##'   are sought.
##' @param parentFlag Logical.  If TRUE (default) this function gets all 
##'   descendants.  If FALSE, it gets all ancestors.
##'   
##' @return A numeric vector containing topNodes as well as all descendants (or
##'   ancestors) of topNodes.
##' 
##' @export
##' 

getChildren = function(commodityTree, parentColname, childColname, topNodes,
                       parentFlag = TRUE){
    
    ## Data Quality Checks
    stopifnot(is(commodityTree, "data.table"))
    stopifnot(c(parentColname, childColname) %in% colnames(commodityTree))
    
    oldNodes = topNodes
    newNodes = topNodes
    while(length(newNodes) > 0){
        if(parentFlag){
            newNodes = commodityTree[get(parentColname) %in% oldNodes,
                                     unique(get(childColname))]
        } else {
            newNodes = commodityTree[get(childColname) %in% oldNodes,
                                     unique(get(parentColname))]
        }
        newNodes = setdiff(newNodes, oldNodes)
        oldNodes = c(oldNodes, newNodes)
    }
    oldNodes
}