These functions allow you to map over the nodes in a graph, by first
performing a depth first search on the graph and then mapping over each
node in the order they are visited. The mapping function will have access to
the result and search statistics for all the nodes between itself and the
root in the search. To map over the nodes in the reverse direction use
`map_dfs_back()`

.

```
map_dfs(root, mode = "out", unreachable = FALSE, .f, ...)
map_dfs_lgl(root, mode = "out", unreachable = FALSE, .f, ...)
map_dfs_chr(root, mode = "out", unreachable = FALSE, .f, ...)
map_dfs_int(root, mode = "out", unreachable = FALSE, .f, ...)
map_dfs_dbl(root, mode = "out", unreachable = FALSE, .f, ...)
```

- root
The node to start the search from

- mode
How should edges be followed?

`'out'`

only follows outbound edges,`'in'`

only follows inbound edges, and`'all'`

follows all edges. This parameter is ignored for undirected graphs.- unreachable
Should the search jump to an unvisited node if the search is completed without visiting all nodes.

- .f
A function to map over all nodes. See Details

- ...
Additional parameters to pass to

`.f`

`map_dfs()`

returns a list of the same length as the number of nodes
in the graph, in the order matching the node order in the graph (that is, not
in the order they are called). `map_dfs_*()`

tries to coerce its result into
a vector of the classes `logical`

(`map_dfs_lgl`

), `character`

(`map_dfs_chr`

), `integer`

(`map_dfs_int`

), or `double`

(`map_dfs_dbl`

).
These functions will throw an error if they are unsuccesful, so they are type
safe.

The function provided to `.f`

will be called with the following arguments in
addition to those supplied through `...`

:

`graph`

: The full`tbl_graph`

object`node`

: The index of the node currently mapped over`rank`

: The rank of the node in the search`rank_out`

: The rank of the completion of the nodes subtree`parent`

: The index of the node that led to the current node`dist`

: The distance of the current node from the root`path`

: A table containing`node`

,`rank`

,`rank_out`

,`parent`

, dist`, and`

result`columns giving the values for each node leading to the current node. The`

result` column will contain the result of the mapping of each node in a list.

Instead of spelling out all of these in the function it is possible to simply
name the ones needed and use `...`

to catch the rest.

Other node map functions:
`map_bfs_back()`

,
`map_bfs()`

,
`map_dfs_back()`

```
# Add a random integer to the last value along a search
create_tree(40, children = 3, directed = TRUE) %>%
mutate(child_acc = map_dfs_int(node_is_root(), .f = function(node, path, ...) {
last_val <- if (nrow(path) == 0) 0L else tail(unlist(path$result), 1)
last_val + sample(1:10, 1)
}))
#> # A tbl_graph: 40 nodes and 39 edges
#> #
#> # A rooted tree
#> #
#> # Node Data: 40 × 1 (active)
#> child_acc
#> <int>
#> 1 8
#> 2 16
#> 3 12
#> 4 18
#> 5 25
#> 6 23
#> # … with 34 more rows
#> #
#> # Edge Data: 39 × 2
#> from to
#> <int> <int>
#> 1 1 2
#> 2 1 3
#> 3 1 4
#> # … with 36 more rows
```