treeDists: Provide objects for determining distances among nodes of a reference tree.

Description

Provides objects (dists, paths) that can be used to calculate vectors of distances between an internal node and each leaf node. Also returns a square matrix of distances between leaf nodes.

Usage

treeDists(placefile, distfile)

Arguments

placefile

path to pplacer output

distfile

path to output of guppy distmat

Value

A list with the following elements:
distsrectangular matrix of distances with rows corresponding to all nodes in pplacer order, and columns corresponding to tips in the order of the corresponding phylo{ape} object.
pathsrectangular matrix in the same configuration as dists with values of 1 or -1 if the path between nodes is serial or parallel, respectively (see Details)
dmatsquare matrix containing distances between pairs of tips.

Details

A placement on an edge looks like this: proximal | | d_p | |---- x | | d_d | | distal d_p is the distance from the placement x to the proximal side of the edge, and d_d the distance to the distal side.

If the distance from x to a leaf y is an S-distance Q, then the path from x to y will go through the distal side of the edge and we will need to add d_d to Q to get the distance from x to y. If the distance from x to a leaf y is a P-distance Q, then the path from x to y will go through the proximal side of the edge, and we will need to subtract off d_d from Q to get the distance from x to y. In either case, we always need to add the length of the pendant edge, which is the second column.

To review, say the values of the two leftmost columns are a and b for a given placement x, and that it is on an edge i. We are interested in the distance of x to a leaf y, which is on edge j. We look at the distance matrix, entry (i,j), and say it is an S-distance Q. Then our distance is Q+a+b. If it is a P-distance Q, then the distance is Q-a+b.

The distances between leaves should always be P-distances, and there we need no trickery.

(thanks to Erick Matsen for this description)

References

Documentation for pplacer and guppy can be found here: http://matsen.fhcrc.org/pplacer/

Examples

Run this code

placefile <- system.file('extdata','merged.json', package='clstutils')
distfile <- system.file('extdata','merged.distmat.bz2', package='clstutils')
treedists <- treeDists(placefile, distfile)

## coordinates of a single placement
placetab <- data.frame(at=49, edge=5.14909e-07, branch=5.14909e-07)

## dvects is a matrix in which each row corresponds to a vector of
## distances between a single placement along the edge of the reference
## tree used to generate 'distfile', and each column correspons to a
## reference sequence (ie, a terminal node).

dvects <- with(placetab, {
treedists$dists[at+1,,drop=FALSE] + treedists$paths[at+1,,drop=FALSE]*edge + branch
})

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