# Calculate vector of shortest distances from a series of 'from' points to nearest one of series of 'to' points. ```r dodgr_dists_nearest( graph, from = NULL, to = NULL, shortest = TRUE, heap = "BHeap", quiet = TRUE ) ``` ## Arguments - `graph`: `data.frame` or equivalent object representing the network graph (see Notes) - `from`: Vector or matrix of points from which route distances are to be calculated (see Notes) - `to`: Vector or matrix of points to which shortest route distances are to be calculated to nearest 'to' point only. - `shortest`: If `FALSE`, calculate distances along the **fastest** rather than shortest routes (see Notes). - `heap`: Type of heap to use in priority queue. Options include Fibonacci Heap (default; `FHeap`), Binary Heap (`BHeap`), `Trinomial Heap (`TriHeap`), Extended Trinomial Heap (`TriHeapExt`, and 2-3 Heap (`Heap23`). - `quiet`: If `FALSE`, display progress messages on screen. ## Returns Vector of distances, one element for each 'from' point giving the distance to the nearest 'to' point. ## Note `graph` must minimally contain three columns of `from`, `to`, `dist`. If an additional column named `weight` or `wt` is present, shortest paths are calculated according to values specified in that column; otherwise according to `dist` values. Either way, final distances between `from` and `to` points are calculated by default according to values of `dist`. That is, paths between any pair of points will be calculated according to the minimal total sum of `weight` values (if present), while reported distances will be total sums of `dist` values. For street networks produced with weight_streetnet , distances may also be calculated along the **fastest** routes with the `shortest = FALSE` option. Graphs must in this case have columns of `time` and `time_weighted`. Note that the fastest routes will only be approximate when derived from `sf`-format data generated with the `osmdata` function `osmdata_sf()`, and will be much more accurate when derived from `sc`-format data generated with `osmdata_sc()`. See weight_streetnet for details. The `from` and `to` columns of `graph` may be either single columns of numeric or character values specifying the numbers or names of graph vertices, or combinations to two columns specifying geographical (longitude and latitude) coordinates. In the latter case, almost any sensible combination of names will be accepted (for example, `fromx, fromy`, `from_x, from_y`, or `fr_lat, fr_lon`.) `from` and `to` values can be either two-column matrices or equivalent of longitude and latitude coordinates, or else single columns precisely matching node numbers or names given in `graph$from` or `graph$to`. If `to` is `NULL`, pairwise distances are calculated from all `from` points to all other nodes in `graph`. If both `from` and `to` are `NULL`, pairwise distances are calculated between all nodes in `graph`. Calculations are always calculated in parallel, using multiple threads. ## Examples ```r # A simple graph graph <- data.frame ( from = c ("A", "B", "B", "B", "C", "C", "D", "D"), to = c ("B", "A", "C", "D", "B", "D", "C", "A"), d = c (1, 2, 1, 3, 2, 1, 2, 1) ) dodgr_dists (graph) # A larger example from the included [hampi()] data. graph <- weight_streetnet (hampi) from <- sample (graph$from_id, size = 100) to <- sample (graph$to_id, size = 50) d <- dodgr_dists (graph, from = from, to = to) # d is a 100-by-50 matrix of distances between `from` and `to` ## Not run: # a more complex street network example, thanks to @chrijo; see # https://github.com/UrbanAnalyst/dodgr/issues/47 xy <- rbind ( c (7.005994, 51.45774), # limbeckerplatz 1 essen germany c (7.012874, 51.45041) ) # hauptbahnhof essen germany xy <- data.frame (lon = xy [, 1], lat = xy [, 2]) essen <- dodgr_streetnet (pts = xy, expand = 0.2, quiet = FALSE) graph <- weight_streetnet (essen, wt_profile = "foot") d <- dodgr_dists (graph, from = xy, to = xy) # First reason why this does not work is because the graph has multiple, # disconnected components. table (graph$component) # reduce to largest connected component, which is always number 1 graph <- graph [which (graph$component == 1), ] d <- dodgr_dists (graph, from = xy, to = xy) # should work, but even then note that table (essen$level) # There are parts of the network on different building levels (because of # shopping malls and the like). These may or may not be connected, so it may # be necessary to filter out particular levels index <- which (!(essen$level == "-1" | essen$level == "1")) # for example library (sf) # needed for following sub-select operation essen <- essen [index, ] graph <- weight_streetnet (essen, wt_profile = "foot") graph <- graph [which (graph$component == 1), ] d <- dodgr_dists (graph, from = xy, to = xy) ## End(Not run) ``` ## See Also Other distances: `dodgr_distances()`, `dodgr_dists()`, `dodgr_dists_categorical()`, `dodgr_flows_aggregate()`, `dodgr_flows_disperse()`, `dodgr_flows_si()`, `dodgr_isochrones()`, `dodgr_isodists()`, `dodgr_isoverts()`, `dodgr_paths()`, `dodgr_times()`

dodgr_dists_nearest function