best.first.search: Best-first search

In FSelector: Selecting attributes

Description

The algorithm for searching atrribute subset space.

Usage

best.first.search(attributes, eval.fun, max.backtracks = 5)

Arguments

attributes	a character vector of all attributes to search in
eval.fun	a function taking as first parameter a character vector of all attributes and returning a numeric indicating how important a given subset is
max.backtracks	an integer indicating a maximum allowed number of backtracks, default is 5

Details

The algorithm is similar to forward.search besides the fact that is chooses the best node from all already evaluated ones and evaluates it. The selection of the best node is repeated approximately max.brackets times in case no better node found.

Value

A character vector of selected attributes.

Author(s)

Piotr Romanski

See Also

forward.search, backward.search, hill.climbing.search, exhaustive.search

Examples

  library(rpart)
  data(iris)
  
  evaluator <- function(subset) {
    #k-fold cross validation
    k <- 5
    splits <- runif(nrow(iris))
    results = sapply(1:k, function(i) {
      test.idx <- (splits >= (i - 1) / k) & (splits < i / k)
      train.idx <- !test.idx
      test <- iris[test.idx, , drop=FALSE]
      train <- iris[train.idx, , drop=FALSE]
      tree <- rpart(as.simple.formula(subset, "Species"), train)
      error.rate = sum(test$Species != predict(tree, test, type="c")) / nrow(test)
      return(1 - error.rate)
    })
    print(subset)
    print(mean(results))
    return(mean(results))
  }
  
  subset <- best.first.search(names(iris)[-5], evaluator)
  f <- as.simple.formula(subset, "Species")
  print(f)

  

Example output

OpenJDK 64-Bit Server VM warning: Can't detect initial thread stack location - find_vma failed
[1] "Sepal.Length"
[1] 0.7346628
[1] "Sepal.Width"
[1] 0.5220969
[1] "Petal.Length"
[1] 0.9527062
[1] "Petal.Width"
[1] 0.9538031
[1] "Sepal.Length" "Petal.Width" 
[1] 0.9567252
[1] "Sepal.Width" "Petal.Width"
[1] 0.9617426
[1] "Petal.Length" "Petal.Width" 
[1] 0.9290652
[1] "Sepal.Length" "Sepal.Width"  "Petal.Width" 
[1] 0.9594957
[1] "Sepal.Width"  "Petal.Length" "Petal.Width" 
[1] 0.9413296
Species ~ Sepal.Width + Petal.Width
<environment: 0x365a0e0>
Warning message:
system call failed: Cannot allocate memory 

FSelector documentation built on May 2, 2019, 4:52 p.m.