```
train(x, ...)
"train"(x, y, method = "rf", preProcess = NULL, ..., weights = NULL, metric = ifelse(is.factor(y), "Accuracy", "RMSE"), maximize = ifelse(metric %in% c("RMSE", "logLoss"), FALSE, TRUE), trControl = trainControl(), tuneGrid = NULL, tuneLength = 3)
"train"(form, data, ..., weights, subset, na.action = na.fail, contrasts = NULL)
```

x

an object where samples are in rows and features are in columns.
This could be a simple matrix, data frame or other type (e.g. sparse
matrix). See Details below.

y

a numeric or factor vector containing the outcome for each sample.

method

a string specifying which classification or regression model
to use. Possible values are found using

`names(getModelInfo())`

. See
http://topepo.github.io/caret/bytag.html. A list of functions can also
be passed for a custom model function. See
http://topepo.github.io/caret/custom_models.html for details.preProcess

a string vector that defines a pre-processing of the
predictor data. Current possibilities are "BoxCox", "YeoJohnson",
"expoTrans", "center", "scale", "range", "knnImpute", "bagImpute",
"medianImpute", "pca", "ica" and "spatialSign". The default is no
pre-processing. See

`preProcess`

and `trainControl`

on the procedures and how to adjust them. Pre-processing code is only
designed to work when `x`

is a simple matrix or data frame.weights

a numeric vector of case weights. This argument will only
affect models that allow case weights.

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

`summaryFunction`

argument
in `trainControl`

, the value of `metric`

should match one
of the arguments. If it does not, a warning is issued and the first metric
given by the `summaryFunction`

is used. (NOTE: If given, this argument
must be named.)maximize

a logical: should the metric be maximized or minimized?

trControl

a list of values that define how this function acts. See

`trainControl`

and
http://topepo.github.io/caret/training.html#custom. (NOTE: If given,
this argument must be named.)tuneGrid

a data frame with possible tuning values. The columns are
named the same as the tuning parameters. Use

`getModelInfo`

to
get a list of tuning parameters for each model or see
http://topepo.github.io/caret/modelList.html. (NOTE: If given, this
argument must be named.)tuneLength

an integer denoting the amount of granularity in the
tuning parameter grid. By default, this argument is the number of levels for
each tuning parameters that should be generated by

`train`

. If
`trainControl`

has the option `search = "random"`

, this is
the maximum number of tuning parameter combinations that will be generated
by the random search. (NOTE: If given, this argument must be named.)form

A formula of the form

`y ~ x1 + x2 + ...`

data

Data frame from which variables specified in

`formula`

are
preferentially to be taken.subset

An index vector specifying the cases to be used in the
training sample. (NOTE: If given, this argument must be named.)

na.action

A function to specify the action to be taken if NAs are
found. The default action is for the procedure to fail. An alternative is

`na.omit`

, which leads to rejection of cases with missing values on any
required variable. (NOTE: If given, this argument must be named.)contrasts

a list of contrasts to be used for some or all the factors
appearing as variables in the model formula.

...

arguments passed to the classification or regression routine
(such as

`randomForest`

). Errors will occur if
values for tuning parameters are passed here.-
A list is returned of class

`train`

containing: containing:`train`

can be used to tune models by picking the complexity parameters
that are associated with the optimal resampling statistics. For particular
model, a grid of parameters (if any) is created and the model is trained on
slightly different data for each candidate combination of tuning parameters.
Across each data set, the performance of held-out samples is calculated and
the mean and standard deviation is summarized for each combination. The
combination with the optimal resampling statistic is chosen as the final
model and the entire training set is used to fit a final model.The predictors in `x`

can be most any object as long as the underlying
model fit function can deal with the object class. The function was designed
to work with simple matrices and data frame inputs, so some functionality
may not work (e.g. pre-processing). When using string kernels, the vector of
character strings should be converted to a matrix with a single column.

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

A variety of models are currently available and are enumerated by tag (i.e. their model characteristics) at http://topepo.github.io/caret/bytag.html.

Kuhn (2008), ``Building Predictive Models in R Using the caret'' (http://www.jstatsoft.org/article/view/v028i05/v28i05.pdf)

`models`

, `trainControl`

,
`update.train`

, `modelLookup`

,
`createFolds`

## Not run: # # ####################################### # ## Classification Example # # data(iris) # TrainData <- iris[,1:4] # TrainClasses <- iris[,5] # # knnFit1 <- train(TrainData, TrainClasses, # method = "knn", # preProcess = c("center", "scale"), # tuneLength = 10, # trControl = trainControl(method = "cv")) # # knnFit2 <- train(TrainData, TrainClasses, # method = "knn", # preProcess = c("center", "scale"), # tuneLength = 10, # trControl = trainControl(method = "boot")) # # # library(MASS) # nnetFit <- train(TrainData, TrainClasses, # method = "nnet", # preProcess = "range", # tuneLength = 2, # trace = FALSE, # maxit = 100) # # ####################################### # ## Regression Example # # library(mlbench) # data(BostonHousing) # # lmFit <- train(medv ~ . + rm:lstat, # data = BostonHousing, # method = "lm") # # library(rpart) # rpartFit <- train(medv ~ ., # data = BostonHousing, # method = "rpart", # tuneLength = 9) # # ####################################### # ## Example with a custom metric # # madSummary <- function (data, # lev = NULL, # model = NULL) { # out <- mad(data$obs - data$pred, # na.rm = TRUE) # names(out) <- "MAD" # out # } # # robustControl <- trainControl(summaryFunction = madSummary) # marsGrid <- expand.grid(degree = 1, nprune = (1:10) * 2) # # earthFit <- train(medv ~ ., # data = BostonHousing, # method = "earth", # tuneGrid = marsGrid, # metric = "MAD", # maximize = FALSE, # trControl = robustControl) # # ####################################### # ## Parallel Processing Example via multicore package # # ## library(doMC) # ## registerDoMC(2) # # ## NOTE: don't run models form RWeka when using # ### multicore. The session will crash. # # ## The code for train() does not change: # set.seed(1) # usingMC <- train(medv ~ ., # data = BostonHousing, # method = "glmboost") # # ## or use: # ## library(doMPI) or # ## library(doParallel) or # ## library(doSMP) and so on # # ## End(Not run)