MRPC (version 2.2.0)

EdgeOrientation: Perform edge orientation under the MRPC algorithm

Description

This function performs the second step of the MRPC algorithm where it determines the edge direction in the graph skeleton inferred by the function ModiSkeleton. If the data contain genetic variants, this function first determines the edges between genetic variants and phenotype nodes based on the principle of Mendelian randomization. Next it identifies potential v-structures and orients the edges in them. For the remaining edges, it examines triplets in turn to see whether a triplet is compatible with one of the basic models. See the references for details.

Usage

EdgeOrientation(gInput, GV, suffStat, FDR, alpha,indepTest, 
                FDRcontrol, verbose = FALSE)

Arguments

gInput

Object containing the skeleton and marginal and conditional independence information.

GV

The number of genetic variants (SNPs/indels/CNV/eQTL) in the input data matrix. For example, if the data has one genetic variant, first column, then GV = 1, if 2, 1st and 2nd Column, then GV = 2, and so on.

suffStat

A list of sufficient statistics containing all necessary elements for the conditional independence tests in the function indepTest for gaussCItest. The sufficient statistics consist of the correlation matrix of the data and the sample size.

FDR

False discovery rate (number between 0 and 1). If FDR = 0.05, this ensures that the FDR and mFDR remains below 0.05.

alpha

Significance level (number in (0,1) for the individual tests.

indepTest

A function for testing conditional independence. It is used to test the conditional independence of x and y given S, called as indepTest(x, y, S, suffStat). Where, x and y are variables, and S is a vector, possibly empty, of variables. suffStat is a list, see the argument above. The return value of indepTest is the p-value of the test for conditional independence. There are three options for different data types, for example, Gaussian data = gaussCItest, discrete data = disCItest and Binary data = binCItest. See help(gaussCItest)

FDRcontrol

(optional) The default is TRUE which implements a sequential FDR control method, otherwise used fixed significance level for the individual tests.

verbose

(optional) 1: detailed output is provided; 0: No output is provided

Value

An object that contains an estimate of the equivalence class of the underlying DAG.

call:

A call object: the original function call.

n:

The sample size used to estimate the graph.

max.ord:

The maximum size of the conditioning set used in the conditional independence tests of the first part of the algorithm.

n.edgetests:

The number of conditional independence tests performed by the first part of the algorithm.

sepset:

Separation sets.

pMax:

A square matrix , where the (i, j)th entry contains the maximal p-value of all conditional independence tests for edge i--j.

graph:

An object of class "'>graph": The undirected or partially directed graph that was estimated.

zMin:

Deprecated.

test:

The number of tests that have been performed.

alpha:

The level of significance for the current test.

R:

A vector of all the decisions made so far from the tests that have been performed.

Details

The orientation of the edge directions based on the principle of Mendelian randomization involves four cases, which are four of the five basic models in Badsha and Fu, 2019 and Badsha et al., 2018. For example, we consider x to be a genetic variant, y and z the phenotype nodes.

The four cases are as follows:

Case-1: Relation between x, genetic variant, and the other nodes. Then genetic variant will regulate the other node, genes, and direction will be genetic variant --> other node. Note that if the data has more than one genetic variant and there is an edge between two genetic variants, then direction will be genetic variant <--> genetic variant, which indicates that there is evidence that the two genetic variants are not independent, but we do not have enough information to determine which genetic variant is the regulator and which is the target.

Case-2: If y and z are adjacent and, x and z are conditionally independent given y, then gene y will regulate the expression of gene z and the edge direction will be y --> z.

Case-3: If y and z are adjacent and, x and z are conditionally dependent given y, then gene z will regulate the expression of gene y and the edge direction will be z --> y.

Case-4: If y and z are adjacent and x and y are conditionally dependent given z and x and z are conditionally dependent given y, then the edge direction will be y <--> z.

References

1. Badsha MB and Fu AQ (2019). Learning causal biological networks with the principle of Mendelian randomization. Frontiers in Genetics, 10(460).

2. Badsha MB, Martin EA and Fu AQ (2018). MRPC: An R package for accurate inference of causal graphs. arXiv arXiv:1806.01899.

See Also

MRPC; ModiSkeleton; SimulateData.

Examples

# NOT RUN {
# Load predefined data
# Data pre-processing

# The 1st column of the input matrix will be the
# genetic variant and the remaining columns are the gene expression data.

# Model 1
Truth <- MRPCtruth$M1   # Truth for model 1
data <- simu_data_M1    # data load for model 1
n <- nrow (data)        # Number of row
V <- colnames(data)     # Column names

# Calculate Pearson correlation
suffStat_C <- list(C = cor(data),
                   n = n)

# Infer a graph skeleton
Skel.fit <- ModiSkeleton(data, 
                         suffStat = suffStat_C, 
                         FDR = 0.05, 
                         alpha = 0.05,
                         indepTest = 'gaussCItest',
                         labels = V,
                         FDRcontrol = TRUE, 
                         verbose = TRUE)

# Edge Orientation
Edge_orientation <- EdgeOrientation(Skel.fit, 
                                    suffStat = suffStat_C, 
                                    GV = 1,
                                    FDR = 0.05,
                                    alpha = 0.05,
                                    indepTest = 'gaussCItest', 
                                    FDRcontrol = TRUE,
                                    verbose = TRUE)
# Plot the results
par(mfrow = c(1, 2))
plot(Truth,
     main = "(A) Truth")
plot(Edge_orientation,
     main = "(B) MRPC ")

# Other models are available and may be called as follows:
# Model 0
# Truth <- MRPCtruth$M0
# data <- simu.data_M0

# Model 2
# Truth <- MRPCtruth$M2
# data <- simu_data_M2

# Model 3
# Truth <- MRPCtruth$M3
# data <- simu_data_M3

# Model 4
# Truth <- MRPCtruth$M4
# data <- simu_data_M4

# Model Multiparent
# Truth <- MRPCtruth$Multiparent
# data <- simu_data_multiparent

# Model Star
# Truth <- MRPCtruth$Star
# data <- simu_data_starshaped

# Model Layered
# Truth <- MRPCtruth$Layered
# data <- simu_data_layered

# }