# layout_as_tree

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##### The Reingold-Tilford graph layout algorithm

A tree-like layout, it is perfect for trees, acceptable for graphs with not too many cycles.

Keywords
graphs
##### Usage
layout_as_tree(graph, root = numeric(), circular = FALSE,
rootlevel = numeric(), mode = "out", flip.y = TRUE)as_tree(...)
##### Arguments
graph
The input graph.
root
The index of the root vertex or root vertices. If this is a non-empty vector then the supplied vertex ids are used as the roots of the trees (or a single tree if the graph is connected). If it is an empty vector, then the root vertices are automatically
circular
Logical scalar, whether to plot the tree in a circular fashion. Defaults to FALSE, so the tree branches are going bottom-up (or top-down, see the flip.y argument.
rootlevel
This argument can be useful when drawing forests which are not trees (i.e. they are unconnected and have tree components). It specifies the level of the root vertices for every tree in the forest. It is only considered if the roots argument i
mode
Specifies which edges to consider when building the tree. If it is out, then only the outgoing, if it is in, then only the incoming edges of a parent are considered. If it is all then all edges are used
flip.y
Logical scalar, whether to flip the y coordinates. The default is flipping because that puts the root vertex on the top.
...
Passed to layout_as_tree.
##### Details

Arranges the nodes in a tree where the given node is used as the root. The tree is directed downwards and the parents are centered above its children. For the exact algorithm, the refernce below.

If the given graph is not a tree, a breadth-first search is executed first to obtain a possible spanning tree.

##### Value

• A numeric matrix with two columns, and one row for each vertex.

##### References

Reingold, E and Tilford, J (1981). Tidier drawing of trees. IEEE Trans. on Softw. Eng., SE-7(2):223--228.

Other graph layouts: add_layout_; as_bipartite, layout.bipartite, layout_as_bipartite; as_star, layout.star, layout_as_star; component_wise; in_circle, layout_in_circle; layout.auto, layout_nicely, nicely; layout.davidson.harel, layout_with_dh, with_dh; layout.gem, layout_with_gem, with_gem; layout.graphopt, layout_with_graphopt, with_graphopt; layout.grid, layout.grid.3d, layout.grid.3d, layout_on_grid, on_grid; layout.mds, layout_with_mds, with_mds; layout.merge, layout_components, merge_coords, piecewise.layout, piecewise.layout; layout.norm, norm_coords; layout.sugiyama, layout_with_sugiyama, with_sugiyama; layout_on_sphere, on_sphere; layout_randomly, randomly; layout_with_fr, with_fr; layout_with_kk, with_kk; layout_with_lgl, with_lgl; layout, layout_, print.igraph_layout_modifier, print.igraph_layout_spec; normalize

##### Aliases
• as_tree
• layout_as_tree
##### Examples
tree <- make_tree(20, 3)
plot(tree, layout=layout_as_tree)
plot(tree, layout=layout_as_tree(tree, flip.y=FALSE))
plot(tree, layout=layout_as_tree(tree, circular=TRUE))

tree2 <- make_tree(10, 3) + make_tree(10, 2)
plot(tree2, layout=layout_as_tree)
plot(tree2, layout=layout_as_tree(tree2, root=c(1,11),
rootlevel=c(2,1)))
Documentation reproduced from package igraph, version 1.0.0, License: GPL (>= 2)

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