rfe {caret} | R Documentation

## Backwards Feature Selection

### Description

A simple backwards selection, a.k.a. recursive feature selection (RFE), algorithm

### Usage

    rfe(x, ...)

    ## Default S3 method:
    rfe(x, y, sizes = 2^(2:4), metric = ifelse(is.factor(y),
      "Accuracy", "RMSE"), maximize = ifelse(metric == "RMSE", FALSE, TRUE),
      rfeControl = rfeControl(), ...)

    rfeIter(x, y, testX, testY, sizes, rfeControl = rfeControl(), label = "",
      seeds = NA, ...)

    ## S3 method for class 'rfe'
    update(object, x, y, size, ...)

### Arguments

`x` | a matrix or data frame of predictors for model training. This object must have unique column names.
`y` | a vector of training set outcomes (either numeric or factor)
`sizes` | a numeric vector of integers corresponding to the number of features that should be retained
`metric` | a string that specifies what summary metric will be used to select the optimal model. By default, possible values are "RMSE" and "Rsquared" for regression and "Accuracy" and "Kappa" for classification. If custom performance metrics are used (via the `functions` argument in `rfeControl`, the value of `metric` should match one of the arguments.
`maximize` | a logical: should the metric be maximized or minimized?
`rfeControl` | a list of options, including functions for fitting and prediction. The web page http://topepo.github.io/caret/featureselection.html#rfe has more details and examples related to this function.
`testX` | a matrix or data frame of test set predictors. This must have the same column names as `x`
`testY` | a vector of test set outcomes
`label` | an optional character string to be printed when in verbose mode.
`seeds` | an optional vector of integers for the size. The vector should have length of `length(sizes)+1`
`object` | an object of class `rfe`
`size` | a single integers corresponding to the number of features that should be retained in the updated model
`...` | options to pass to the model fitting function (ignored in `predict.rfe`)

### Details

More details on this function can be found at http://topepo.github.io/caret/featureselection.html.

This function implements backwards selection of predictors based on predictor importance ranking. The predictors are ranked and the less important ones are sequentially eliminated prior to modeling. The goal is to find a subset of predictors that can be used to produce an accurate model. The web page http://topepo.github.io/caret/featureselection.html#rfe has more details and examples related to this function.

`rfe` can be used with "explicit parallelism", where different resamples (e.g. cross-validation group) can be split up and run on multiple machines or processors. By default, `rfe` will use a single processor on the host machine. As of version 4.99 of this package, the framework used for parallel processing uses the foreach package. To run the resamples in parallel, the code for `rfe` does not change; prior to the call to `rfe`, a parallel backend is registered with foreach (see the examples below).

`rfeIter` is the basic algorithm while `rfe` wraps these operations inside of resampling. To avoid selection bias, it is better to use the function `rfe` than `rfeIter`.

When updating a model, if the entire set of resamples were not saved using `rfeControl(returnResamp = "final")`, the existing resamples are removed with a warning.

### Value

A list with elements

`finalVariables` | a list of size `length(sizes) + 1` containing the column names of the “surviving” predictors at each stage of selection. The first element corresponds to all the predictors (i.e. `size = ncol(x)`)
`pred` | a data frame with columns for the test set outcome, the predicted outcome and the subset size.

### Author(s)

Max Kuhn

### See Also

`rfeControl`

### Examples

    ## Not run:
    data(BloodBrain)

    x <- scale(bbbDescr[,-nearZeroVar(bbbDescr)])
    x <- x[, -findCorrelation(cor(x), .8)]
    x <- as.data.frame(x)

    set.seed(1)
    lmProfile <- rfe(x, logBBB,
                     sizes = c(2:25, 30, 35, 40, 45, 50, 55, 60, 65),
                     rfeControl = rfeControl(functions = lmFuncs,
                                             number = 200))
    set.seed(1)
    lmProfile2 <- rfe(x, logBBB,
                     sizes = c(2:25, 30, 35, 40, 45, 50, 55, 60, 65),
                     rfeControl = rfeControl(functions = lmFuncs,
                                             rerank = TRUE,
                                             number = 200))

    xyplot(lmProfile$results$RMSE + lmProfile2$results$RMSE  ~
           lmProfile$results$Variables,
           type = c("g", "p", "l"),
           auto.key = TRUE)

    rfProfile <- rfe(x, logBBB,
                     sizes = c(2, 5, 10, 20),
                     rfeControl = rfeControl(functions = rfFuncs))

    bagProfile <- rfe(x, logBBB,
                      sizes = c(2, 5, 10, 20),
                      rfeControl = rfeControl(functions = treebagFuncs))

    set.seed(1)
    svmProfile <- rfe(x, logBBB,
                      sizes = c(2, 5, 10, 20),
                      rfeControl = rfeControl(functions = caretFuncs,
                                              number = 200),
                      ## pass options to train()
                      method = "svmRadial")

    ## classification

    data(mdrr)
    mdrrDescr <- mdrrDescr[,-nearZeroVar(mdrrDescr)]
    mdrrDescr <- mdrrDescr[, -findCorrelation(cor(mdrrDescr), .8)]

    set.seed(1)
    inTrain <- createDataPartition(mdrrClass, p = .75, list = FALSE)[,1]

    train <- mdrrDescr[ inTrain, ]
    test  <- mdrrDescr[-inTrain, ]
    trainClass <- mdrrClass[ inTrain]
    testClass  <- mdrrClass[-inTrain]

    set.seed(2)
    ldaProfile <- rfe(train, trainClass,
                      sizes = c(1:10, 15, 30),
                      rfeControl = rfeControl(functions = ldaFuncs, method = "cv"))
    plot(ldaProfile, type = c("o", "g"))

    postResample(predict(ldaProfile, test), testClass)

    ## End(Not run)

    #######################################
    ## Parallel Processing Example via multicore

    ## Not run:
    library(doMC)

    ## Note: if the underlying model also uses foreach, the
    ## number of cores specified above will double (along with
    ## the memory requirements)
    registerDoMC(cores = 2)

    set.seed(1)
    lmProfile <- rfe(x, logBBB,
                     sizes = c(2:25, 30, 35, 40, 45, 50, 55, 60, 65),
                     rfeControl = rfeControl(functions = lmFuncs,
                                             number = 200))

    ## End(Not run)

[Package caret version 6.0-73 Index]