EdgeRatio()

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: TreeTools
 Title: Create, Modify and Analyse Phylogenetic Trees
-Version: 2.1.0.9000
+Version: 2.1.0.9001
 Authors@R: c(
   person("Martin R.", 'Smith', role = c("aut", "cre", "cph"), 
          email = "martin.smith@durham.ac.uk",

NAMESPACE

@@ -53,6 +53,7 @@ S3method(DropTip,Splits)
 S3method(DropTip,list)
 S3method(DropTip,multiPhylo)
 S3method(DropTip,phylo)
+S3method(EdgeRatio,phylo)
 S3method(KeepTip,"NULL")
 S3method(KeepTip,Splits)
 S3method(KeepTip,list)
@@ -298,6 +299,7 @@ export(DropTip)
 export(DropTipPhylo)
 export(EdgeAncestry)
 export(EdgeDistances)
+export(EdgeRatio)
 export(EndSentence)
 export(ExtractTaxa)
 export(FirstMatchingSplit)

NEWS.md

@@ -1,3 +1,7 @@
+# TreeTools 2.1.0.9001 (2026-02-19) #
+
+- `EdgeRatio()` reports the ratio of external:internal edges.
+
 # TreeTools 2.1.0.9000 (2026-02-16) #
 
 - `SplitInformation()` supports `Splits` and `phylo` objects.

R/EdgeRatio.R

@@ -0,0 +1,34 @@
+#' Ratio of external:internal edge length
+#' 
+#' Reports the ratio of tree length associated with external edges (i.e.
+#' edges whose child is a leaf) and internal edges.
+#' Where tree length is dominated by internal edges, variation between tips
+#' is dominantly controlled by phylogenetic history.
+#' 
+#' @param x A tree of class \code{\link[ape:read.tree]{phylo}}.
+#' @returns `EdgeRatio()` returns a numeric specifying the ratio of external
+#' to internal edge length (> 1 means the length of a tree is predominantly
+#' in external edges), with attributes `external`, `internal`, and `total`
+#' specifying the total length associated with edges of that nature.
+#' @template MRS
+#' @export
+EdgeRatio <- function(x) UseMethod("EdgeRatio")
+
+#' @rdname EdgeRatio
+#' @export
+EdgeRatio.phylo <- function(x) {
+  el <- x[["edge.length"]]
+  if (is.null(el)) {
+    warning("Edge lengths not specified")
+    return(NA_real_)
+  }
+  ed <- x[["edge"]]
+  nTip <- NTip(x)
+  external <- ed[, 2] <= nTip
+  exLen <- sum(el[external])
+  inLen <- sum(el[!external])
+  structure(exLen / inLen,
+            external = exLen,
+            internal = inLen,
+            total = sum(exLen, inLen))
+}

tests/testthat/test-EdgeRatio.R

@@ -0,0 +1,9 @@
+test_that("EdgeRatio() works", {
+  expect_warning(expect_equal(EdgeRatio(BalancedTree(5)), NA_real_),
+                 "[Ee]dge lengths not spec")
+
+  ex2 <- BalancedTree(4)
+  ex2[["edge.length"]] <- c(1, 2, 2, 1, 2, 2)
+  expect_equal(EdgeRatio(ex2),
+               structure(8/2, external = 8, internal = 2, total = 10))
+})