### Description

`dDAGancestor`

is supposed to find a list of common ancestors
shared by two terms/nodes, given a direct acyclic graph (DAG; an
ontology). If two terms are given as NULL, then a sparse matrix of
children x ancestors is built for all terms. If one of them is null,
then a sparse matrix of children x ancestors is built but only for
non-null input terms.

### Usage

dDAGancestor(g, term1 = NULL, term2 = NULL, verbose = T)

### Arguments

- g
- an object of class "igraph" or "graphNEL"
- term1
- the first term/node as input
- term2
- the second term/node as input
- verbose
- logical to indicate whether the messages will be
displayed in the screen. By default, it sets to true for display

### Value

- When two terms are given: a list of terms/nodes that are common
ancestors for two input terms/nodes
- When two terms are given as NULL: a sparse matrix of children x
ancestors is built for all terms, with '1' for the reachable and
otherwise '0'.
- When one of terms is given as NULL: a sparse matrix of children x
ancestors is built but only for non-null input terms, with '1' for the
reachable and otherwise '0'.

### Note

none

### Examples

# 1) load HPPA as igraph object
ig.HPPA <-dRDataLoader(RData='ig.HPPA')

**'ig.HPPA' (from package 'dnet' version 1.1.2) has been loaded into the working environment (at 2018-01-19 12:34:33)**
g <- ig.HPPA
# 2) randomly give two terms
term1 <- sample(V(g)$name,1)
term2 <- sample(V(g)$name,1)
# 3) find common ancestors
dDAGancestor(g, term1, term2)

**Find common ancestors shared by HP:0002152 and HP:0009523 (2018-01-19 12:34:33)...**
[1] "HP:0000118"