June 2018 Update

Task/Evolutionary-algorithm/R/evolutionary-algorithm-2.r

@@ -0,0 +1,34 @@
+# Setup
+set.seed(42)
+target= unlist(strsplit("METHINKS IT IS LIKE A WEASEL", ""))
+chars= c(LETTERS, " ")
+C= 100
+
+# Fitness function; high value means higher fitness
+fitness= function(x){
+  sum(x == target)
+}
+
+# Mutate function
+mutate= function(x, rate= 0.01){
+  idx= which(runif(length(target)) <= rate)
+  x[idx]= replicate(n= length(idx), expr= sample(x= chars, size= 1, replace= T))
+  x
+}
+
+# Evolve function
+evolve= function(x){
+  parents= rep(list(x), C+1) # Repliction
+  parents[1:C]= lapply(parents[1:C], function(x) mutate(x)) # Mutation
+  idx= which.max(lapply(parents, function(x) fitness(x))) # Selection
+  parents[[idx]]
+}
+
+# Initialize first parent
+parent= sample(x= chars, size= length(target), replace= T)
+
+# Main program
+while (fitness(parent) < fitness(target)) {
+  parent= evolve(parent)
+  cat(paste0(parent, collapse=""), "\n")
+}