如何在R中使用Apply函数删除循环

Question

I have a matrix

A <- matrix(c(1,2,1,2,4,4,6,7,6),nrow=3,ncol=3)

So basically I am replacing each element with the frequency of it occurring as seen in the corresponding column and taking the product of all the elements in the row.

My approach

fr <- c(paste("fr", 1:97, sep = ""))
for(i in 1:3){assign(fr[i],table(A[,i]))}
prob=matrix(c(rep(1,3)),3, byrow = T)
for (i in 1:3)
{
   for (j in 1:3)
{
    prob[i]<-prob[i]*get(fr[j])[as.character(A[i,j])]
}
}

Is there any way to solve this without writing loops, using the matrix structure?

I think we can use the apply

I am using R language

Answer 1

Your matrix:

A <- matrix(c(1,2,3,4,5,6,1,4,6), ncol=3, byrow=T)

Apply colwise a function that calculates the probability table:

B <- apply(A, 2, function(x) prop.table(table(x))[as.character(x)])
#           [,1]      [,2]      [,3]
# [1,] 0.6666667 0.3333333 0.3333333
# [2,] 0.3333333 0.3333333 0.6666667
# [3,] 0.6666667 0.3333333 0.6666667

Calculate the product rowwise:

apply(B, 1, prod)
#[1] 0.07407407 0.07407407 0.14814815