MXM (version 0.4.3)

gSquare: G square conditional independence test for discrete data based on the log likelihood ratio test.

Description

The main task of this test is to provide a p-value PVALUE for the null hypothesis: feature 'X' is independent from 'TARGET' given a conditioning set CS. This test is based on the log likelihood ratio test.

Usage

gSquare(target, dataset, xIndex, csIndex, dataInfo = NULL, univariateModels = NULL,
hash = FALSE, stat_hash = NULL, pvalue_hash = NULL)

Arguments

target

A numeric vector containing the values of the target variable.

dataset

A numeric data matrix containing the variables for performing the test. Rows as samples and columns as features.

xIndex

The index of the variable whose association with the target we want to test.

csIndex

The indices of the variables to condition on.

dataInfo

list object with information on the structure of the data. Default value is NULL.

univariateModels

Fast alternative to the hash object for univariate test. List with vectors "pvalues" (p-values), "stats" (statistics) and "flags" (flag = TRUE if the test was succesful) representing the univariate association of each variable with the target. Default val

hash

A boolean variable which indicates whether (TRUE) or not (FALSE) to use the hash-based implementation of the statistics of SES. Default value is FALSE. If TRUE you have to specify the stat_hash argument and the pvalue_hash argument.

stat_hash

A hash object (hash package required) which contains the cached generated statistics of a SES run in the current dataset, using the current test.

pvalue_hash

A hash object (hash package required) which contains the cached generated p-values of a SES run in the current dataset, using the current test.

Value

• A list including:
• pvalue
  A numeric value that represents the generated p-value due to Fisher's method (see reference below).
• stat
  A numeric value that represents the generated statistic due to Fisher's method (see reference below).
• flag
  A numeric value (control flag) which indicates whether the test was succesful (0) or not (1).
• stat_hash
  The current hash object used for the statistics. See argument stat_hash and details. If argument hash = FALSE this is NULL.
• pvalue_hash
  The current hash object used for the p-values. See argument stat_hash and details. If argument hash = FALSE this is NULL.

Details

If hash = TRUE, testIndLogistic requires the arguments 'stat_hash' and 'pvalue_hash' for the hash-based implementation of the statistic test. These hash Objects are produced or updated by each run of SES (if hash == TRUE) and they can be reused in order to speed up next runs of the current statistic test. If "SESoutput" is the output of a SES run, then these objects can be retrieved by SESoutput@hashObject$stat_hash and the SESoutput@hashObject$pvalue_hash. Important: Use these arguments only with the same dataset that was used at initialization.

See Also

SES, testIndFisher, testIndLogistic, censIndLR

Examples

#simulate a dataset with binary data
dataset <- matrix(nrow = 50 , ncol = 101)
dataset <- apply(dataset, 2, function(i) sample(c(0,1),50, replace=TRUE))
#initialize binary target
target <- dataset[,101]
#remove target from the dataset
dataset <- dataset[,-101]

require(pcalg)

if(require("pcalg", quietly = TRUE))
{
  #run the gSquare conditional independence test for the binary class variable
  results <- gSquare(target, dataset, xIndex = 44, csIndex = c(10,20))
  results
  
  #require(gRbase) #for faster computations in the internal functions
  #run SES algorithm using the gSquare conditional independence test for the binary class variable
  sesObject <- SES(target , dataset , max_k=3 , threshold=0.05 , test="gSquare");
  #print summary of the SES output
  summary(sesObject);
  #plot the SES output
  plot(sesObject, mode="all");
}