dodgr_paths documentation

[RegularnaMatrica]

Hi, I've noticed that dodgr_paths don't use weight column if present (dodgr_graph_cols and make_vert_map dont use weight column) , but according to the documentation: If an additional column named weight or wt is present, shortest paths are calculated according to values specified in that column.

Currently I bypass this by:

graph[["d_weighted_orig"]] <- graph[["d_weighted"]]
in the loop ...
    penalty_vec <- ...
    graph[["d_weighted"]] <- graph[["d_weighted_orig"]] * penalty_vec
    ...

[mpadge]

Thanks @RegularnaMatrica. In this case, I think it's just the documentation that needs a little clarifying. Either "weight" or "d_weighted" will be used, but with graphs constructed from SC-data, "d_weighted" always gets preference. The following code (based on your original area from #305) shows that a "weight" column is picked up nevertheless:

library (dodgr)
packageVersion ("dodgr")
#> [1] '0.4.3.13'
bb <- c (16.3, 46.28, 16.5, 46.38)
net <- dodgr_streetnet_sc (bb, expand = 0)
graph <- weight_streetnet (net, wt_profile = "motorcar", turn_penalty = FALSE)
#> Warning: 'oneway' column has ambiguous values; should be TRUE/FALSE or
#> 'yes'/'no' only

cols <- c (".vx0", ".vx1", "d", "d_weighted")
graph0 <- graph1 <- data.frame (graph [, cols])

Paths are then automatically be routed according to "d_weighted":

set.seed (2L)
from <- sample (graph$.vx0, size = 1L)
to <- sample (graph$.vx1, size = 1L)
p0 <- dodgr_paths (graph, from, to)

Or if the column is called "weight", the results remain identical:

names (graph1) [4] <- "weight"
p1 <- dodgr_paths (graph1, from, to)
identical (p0, p1)
#> [1] TRUE

But if there is no "weight" column, paths will use "d", and so (generally) be different:

graph1$weight <- NULL
p2 <- dodgr_paths (graph1, from, to)
identical (p0, p2)
#> [1] FALSE

^{Created on 2025-09-30 with reprex v2.1.1}

(Note that that's a pretty small network, so the ifnal p2 quite often remains identical, but in general, paths with d are different from those with weighted distances.)

---

Would you like to submit a pull request updating the docs for dodgr_paths()? With all the debugging help you've given, it'd be great to see you make direct contributions to the code here. The code which determines the weighted distance column is here:

dodgr/R/graph-functions-misc.R

Lines 112 to 128 in b0841a2

	find_w_col <- function (graph) {
	w_col <- match (c ("w", "wt"), names (graph))
	if (all (is.na (w_col)) || length (w_col) != 1) {
	w_col <- grep ("weight", names (graph))
	}
	if (length (w_col) != 1) {
	w_col <- which (tolower (substring (names (graph), 1, 2)) == "dw" |
	tolower (substring (names (graph), 1, 3)) == "d_w")
	}
	if (length (w_col) > 1) {
	stop ("Unable to determine weight column in graph")
	}
	return (w_col)
	}

If that function find no matching column, then paths are calculated according to distance. I would no longer write that function the way I did back then (2017-2018, according to git blame), so feel free to also update that if you like.

[RegularnaMatrica]

I've tried to write more 'cleaner' documentation, but I failed. It's hard to write 'clean' documentation while 'find columns' functions are so flexible. Another complicating factor is that, dodgr_graph_cols handles columns differently for dodgr_streetnet compared to other objects (which includes dodgr_streetnet_sc).

Nontheless, I think that following changes are necessary:

Currently first if in find_w_col is always TRUE becasue length is 2. I tihnk that idea is to take one of c("weight", "wt", "w") columns as weight (if present, and with that order of 'importance').

find_w_col <- function (graph) {
  
  w_col <- match (c ("weight", "wt", "w"), tolower( names (graph)))
  w_col <- w_col[! is.na (w_col)]
  
  if(length (w_col) > 1) {
    return (w_col[[1]])
  }
    
  w_col <- grep ("weight", names (graph))
  
  if (length (w_col) != 1) {
    w_col <- which (tolower (substring (names (graph), 1, 2)) == "dw" |
                      tolower (substring (names (graph), 1, 3)) == "d_w")
  }
  
  if (length (w_col) != 1) {
    stop ("Unable to determine weight column in graph")
  }
  
  return (w_col)
}

also, in dodgr_graph_cols fallback to distance column won't work because it will stop if it does not find weight column:

w_col <- try (find_w_col (graph), silent = TRUE)
# sc ensures this never happens, so not covered
if (inherits (w_col, "try-error")) {
    w_col <- d_col # nocov
}