to calculate the Entropy - r

Question

I am new to R and unable to calculate the entropy.
There is a similar question on stackoverflow with the answer but i wanted to know why this code isn't working. Here is the copy paste data from the same question.
One of the answer mentions, "The part I think you are missing is the calculation of the class frequencies and you will get your answer", but how do i fix this. I tried most of the options but still i don't get any output. It just runs without any errors.
info <- function(CLASS.FREQ){
freq.class <- CLASS.FREQ
info <- 0
for(i in 1:length(freq.class)){
if(freq.class[[i]] != 0){ # zero check in class
entropy <- -sum(freq.class[[i]] * log2(freq.class[[i]])) #I calculate the entropy for each class i here
}else{
entropy <- 0
}
info <- info + entropy # sum up entropy from all classes
}
return(info)
}
Dataset as below,
buys <- c("no", "no", "yes", "yes", "yes", "no", "yes", "no", "yes", "yes", "yes", "yes", "yes", "no")
credit <- c("fair", "excellent", "fair", "fair", "fair", "excellent", "excellent", "fair", "fair", "fair", "excellent", "excellent", "fair", "excellent")
student <- c("no", "no", "no","no", "yes", "yes", "yes", "no", "yes", "yes", "yes", "no", "yes", "no")
income <- c("high", "high", "high", "medium", "low", "low", "low", "medium", "low", "medium", "medium", "medium", "high", "medium")
age <- c(25, 27, 35, 41, 48, 42, 36, 29, 26, 45, 23, 33, 37, 44)
we change the age from categorical to numeric
Cheers, Jack

Answer 1

You need to calculate the propertion of "no" and "yes" in "buys", the proportion of "fair" and "excellent" in "credit", and so on. Here is one way to do it:
data <- list(
buys = c("no", "no", "yes", "yes", "yes", "no", "yes", "no", "yes", "yes", "yes", "yes", "yes", "no"),
credit = c("fair", "excellent", "fair", "fair", "fair", "excellent", "excellent", "fair", "fair", "fair", "excellent", "excellent", "fair", "excellent"),
student = c("no", "no", "no","no", "yes", "yes", "yes", "no", "yes", "yes", "yes", "no", "yes", "no"),
income = c("high", "high", "high", "medium", "low", "low", "low", "medium", "low", "medium", "medium", "medium", "high", "medium"),
age = c(25, 27, 35, 41, 48, 42, 36, 29, 26, 45, 23, 33, 37, 44)
)
freq <- lapply( data, function(x){rowMeans(outer(unique(x),x,"=="))})
.
> freq
$buys
[1] 0.3571429 0.6428571
$credit
[1] 0.5714286 0.4285714
$student
[1] 0.5 0.5
$income
[1] 0.2857143 0.4285714 0.2857143
$age
[1] 0.07142857 0.07142857 0.07142857 0.07142857 0.07142857 0.07142857 0.07142857 0.07142857 0.07142857 0.07142857 0.07142857 0.07142857 0.07142857
[14] 0.07142857
Such a proportion can never be 0. So change if(freq.class[[i]] != 0){ # zero check in class to if(length(freq.class[[i]]) != 0){ # zero check in class:
info <- function(CLASS.FREQ){
freq.class <- CLASS.FREQ
info <- 0
for(i in 1:length(freq.class)){
if(length(freq.class[[i]]) != 0){ # zero check in class
entropy <- -sum(freq.class[[i]] * log2(freq.class[[i]])) #I calculate the entropy for each class i here
}else{
entropy <- 0
}
info <- info + entropy # sum up entropy from all classes
}
return(info)
}
.
> info(freq)
[1] 8.289526
> info(freq$buys)
[1] 0.940286
> info(freq$age)
[1] 3.807355
>