node.map: Build network node sequence
In travelr: Functions for Travel Demand Modeling

Description Usage Arguments Details Value Author(s) See Also Examples

Map network nodes to a continuous sequence

map.highway.nodes(nodes, numZones )
## S3 method for class 'highway.node.map'
summary(object,...)
## S3 method for class 'highway.node.map'
print(x,...)

`nodes`	An optional node specification, typically a `data.frame`, that can contain useful information such as geographical coordinates
`numZones`	The number of zones (origins and destinations) in the network. The zones must have sequential numbers from `1` to `numZones`
`object`	The `highway.node.map` object to be summarized
`x`	The `highway.node.map` object to be printed
`...`	Additional arguments passed to generic methods

map.highway.nodes builds a highway.node.map structure that can be used to convert a sequence of nodes with gaps to a compact sequence of integers with no missing values. The structure has functions to support mapping and unmapping nodes, as illustrated in the examples.

map.highway.nodes needs to know the number of zones (origins or destinations) in the system, since zones are never renumbered: they have to be continuous from 1 to however many zones there are, and the input network will need to be edited if that is not the case.

Travel models are often coded to leave gaps in node number sequences in order to facilitate editing. Such gaps cause performance problems when they are left in place, and map.highway.nodes is a simple tool for converting an integer sequence with gaps into a continuous sequence, and recovering the original sequence later from the continuous sequence.

Note:The standard R factor utility can also be used to construct a suitable node mapping, either alone or in conjunction with map.highway.nodes. The sequence with gaps can be converted to a factor, and the resulting factor codes will serve as a suitable sequence. Either approach can be used successfully, provided one carefully handles zone numbering. In particular, if the maximum zone number in the original network is, say, 250, but there is a range of numbers from 176 to 200 that are not used, then the correct value for the network numZones parameter after applying the R function factor is 225. map.highway.nodes will catch this situation and force the user to address it explicitly, saving much grief later on.

Returns a highway.node.map object, with two functions, map and unmap that can be used to map and unmap nodes

Jeremy Raw

as.highway.net

numZones <- 5
bad.nodes <- c(1:numZones,round(runif(15,min=6,max=100)))
nodeMap <- map.highway.nodes(bad.nodes,numZones)
good.nodes <- nodeMap$map(bad.nodes)
bad.nodes.2 <- nodeMap$unmap(good.nodes)
results <- data.frame(Original=bad.nodes,Mapped=good.nodes,Unmapped=bad.nodes.2)
all( results$Original==results$Unmapped )