R：计算两个顶点之间的单个最短路径

Question

Currently, I am working on a project that involves NYC Taxi data, in which I am given where a person is picked up and dropped off in a network.

I am working with an ESRI shapefile , which I can load into R as an igraph object with the shp2graph package; I need to utilize Dijkstra's algorithm (or a similar shortest-path algorithm) to find the single shortest path between two given vertices. I thought that the get.shortest.paths() method of the igraph package would be my solution, but to my surprise, this calculates all shortest paths from a vertex to all others in a network.

To me, this seems like overkill, because I need only one single path between two specified nodes. I did some poking around online and in the igraph documentation, but all I can find are methods surrounding calculating many shortest paths from a given vertex to all others.

Due to how computationally expensive it would be to calculate every single shortest path from a vertex, and then just select one from the behemoth of a list, I'm looking for a way to utilize Dijkstra's algorithm between two specified vertices in a graph. Is there a way to do this in the igraph package, or if not, is there a good way to do this with a different package in R?

EDIT: In the end, I am hoping to look for a function that will take in the graph object and the ID of two vertices I wish to find the shortest path between, then return a list of paths/edges (or IDs) along that shortest path. This would help me to inspect each individual street along the shortest path between the two vertices.

EDIT: As an example of how I am currently using the function: path <- get.shortest.paths(NYCgraph, from=32, mode="out") . Something I would hope to find is path <- shortestPathFunction(NYCgraph, from=32, to=37) to arbitrary calculate a shortest path between vertex ID 32 and vertex ID 37 (two random street intersections in the network).

Answer 1

I found my issue, which occurred before I called get.shortest.paths(). For those who are curious on how to read in an ESRI shapefile, and find a single shortest path between two points (which was my dilemma):

myShapefile <- readOGR(dsn=".", layer="MyShapefileName") # i.e. "MyShapefileName.shp"
shpData <- readshpnw(myShapefile, ELComputed=TRUE)
igraphShpObject <- nel2igraph(shpData[[2]], shpData[[3]], weight=shpData[[4]])
testPath <- get.shortest.paths(igraphShpObject, from=42, to=52) # arbitrary nodes
testPath[1] # print the node IDs to the console

Furthermore, if one was interested in getting the ID of the edge connecting two nodes (perhaps from nodes in the testPath):

get.edge.ids(igraphShpObject, c(42,45) # arbitrary nodes 42 and 45

This indexing is the same as the indexing in shpData; for example, if you want to get the length of edge ID x, as found in get.edge.ids() , you may type shpData[[4]][x] .

I hope these tidbits may be helpful to somebody in the future encountering the same problems! This method utilizes the shp2graph , rgdal , and igraph packages in R.