Returns the ids of the sister(s) of nd ids given.
Details
An error is raised if there is no sister (e.g. for the root). There can be more than one sister if tree is polytomous. Parallelizable.
Examples
tree <- randTree(10)
getNdsSstr(tree, ids = tree["tips"])
#> [1] "t9" "t3" "t8" "t10" "t6" "n8" "t4" "n7" "t2" "t1"