Logical specifying return format; see "value" section`.
Value
If fullMatrix = TRUE, PathLengths() returns a square matrix in
which entry [i, j] denotes the distance from internal node i to the
descendant vertex j.
Vertex pairs without a continuous directed path are denoted NA.
If fullMatrix = FALSE, PathLengths() returns a data.frame with three
columns: start lists the deepest node in each path (i.e. that closest
to the root); end lists the shallowest node (i.e. that closest to a leaf);
length lists the total length of that path.