#'
#' Entropy Gain of a Categorical Variable
#'
#' @param target Depedent Variable
#' @param variable Indepedent Variable
#'
#' @return Entropy Gain Score
#'
#' @examples
#' variable=c("A","A","B","A","B","B","B","C","C","C","C","B",
#' "B","B","A","A","C","C","C","C")
#' target = c(1,0,0,0,2,1,1,2,1,2,2,1,1,0,1,2,1,0,2,1)
#' entropyGain(target,variable)
#'
entropyGain <- function(target,variable) {
data_ <- data.frame(variable=variable,
target=target)
if(is.factor(variable)){
pred_parent <- data.frame(table(data_$target))
pred_parent$pred <- pred_parent$Freq/sum(pred_parent$Freq)
# print(pred_parent)
entropy_parent <- -sum(pred_parent$pred*log2(pred_parent$pred))
print(entropy_parent)
tot_tab <- data.frame(table(data_$variable,data_$target))
entropy_variable <- 0
for (i in unique(tot_tab$Var1)){
sub_tab <- tot_tab[which(tot_tab$Var1 == i),]
sub_tab$pred <- sub_tab$Freq/sum(sub_tab$Freq)
# print(sub_tab)
g_sub <- -sum(sub_tab$pred*log2(sub_tab$pred))
# print(g_sub)
p_sub <- (sum(sub_tab$Freq)/sum(tot_tab$Freq))
entropy_variable <- entropy_variable + (p_sub*g_sub)
}
print(entropy_variable)
print(entropy_parent - entropy_variable)
return(entropy_parent - entropy_variable)
} else if(!is.factor(variable)){
return(0)
}
}
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