Aggregate child values of a Node, recursively.
The Aggregate method lets you fetch an attribute from a Node's children, and then aggregate them
using aggFun. For example, you can aggregate cost by summing costs of child Nodes. This is especially useful in the
context of tree traversal, when using post-order traversal mode.
Aggregate(node, attribute, aggFun, ...)
node |
the |
attribute |
determines what is collected. The
|
aggFun |
the aggregation function to be applied to the children's |
... |
any arguments to be passed on to attribute (in case it's a function) |
As with Get, the attribute can be a field, a method or a function. If the attribute on a child
is NULL, Aggregate is called recursively on its children.
data(acme)
#Aggregate on a field
Aggregate(acme, "cost", sum)
#This is the same as:
HomeRolledAggregate <- function(node) {
sum(sapply(node$children, function(child) {
if (!is.null(child$cost)) child$cost
else HomeRolledAggregate(child)
}))
}
HomeRolledAggregate(acme)
#Aggregate using Get
print(acme, "cost", minCost = acme$Get(Aggregate, "cost", min))
#use Aggregate with a function:
Aggregate(acme, function(x) x$cost * x$p, sum)
#cache values along the way
acme$Do(function(x) x$cost <- Aggregate(x, "cost", sum), traversal = "post-order")
acme$IT$costPlease choose more modern alternatives, such as Google Chrome or Mozilla Firefox.