Extractor Functions for bootstrap and other resample objects.

DESCRIPTION:

These functions extract information from , , and other resample objects, or create it if necessary.

resampGetIndices extracts a matrix of resampling indices from a resampling object, or creates it from scratch if necessary.

resampGetArgument extracts arguments used to create resample objects.

USAGE:

resampGetIndices(object, frame.eval = <<see below>>) 
resampGetArgument(object, argument, checkObject = <<see below>>, 
                  frame.eval = <<see below>>) 

REQUIRED ARGUMENTS:

object
a or other resample object (not all such objects are appropriate for these functions).
argument
the quoted or unquoted name of an argument to the resample function used to create object.

OPTIONAL ARGUMENTS:

checkObject
logical; if TRUE, look first in object for a component with name equal to argument. This is the default action unless argument equals "B", in which case the value is recreated from the original call to the resample function.
frame.eval
frame where the data and other objects used when creating object can be found. You need to specify this if objects can't be found by their original names, or have changed; see .

VALUE:

resampGetIndices returns a matrix of indices.

resampGetArgument returns the value of argument, evaluated in an appropriate context.

The context is important in two cases. First, if the object were created inside a function and made use of objects defined in that function, then those objects, or identical copies, should be accessible; this is done by letting frame.eval be the number of the frame of that function, or a new frame containing copies of those objects. Second, if the data argument to the resample function is a data frame, that data frame, then arguments like group and subject are searched for there first.

DETAILS:

resampGetIndices just extracts an indices component if one exists in the object. Otherwise it creates a new call to the original function, with the statistic set to a function that returns NULL. Results will be incorrect if the sampler is adaptive, where indices depend on the value of the statistic returned in earlier replications.

If checkObject=TRUE, resampGetArgument first checks object for a component with name equal to argument and, if found, returns that value. If the component is not found (or if checkObject=FALSE), the argument is reconstructed from the original call. Symbolic references in the call (as in the case where the bootstrap data argument is a data frame, and group is the name of a column of data) are evaluated so that the actual value of the argument is returned. Note that this may cause unintended results in the case argument="statistic": if statistic is an expression, the expression is evaluated (if possible) and that value returned. If you want the unevaluated expression for an argument, access the component directly, using, for example, object$call$statistic.

The special default action when argument="B" addresses the case when bootstrap argument B is a vector. In this case, the value stored in the bootstrap object is not the vector, but sum(B), the total number of resamples. The original vector B can be recreated from the call.

SEE ALSO:

, , , .

EXAMPLES:

# get indices 
boot <- bootstrap(stack.loss, mean, B=50) 
resampGetIndices(boot) 
 
# get group argument 
df <- data.frame(x=stack.loss, a=rep(1:3, 6:8)) 
boot <- bootstrap(df, mean(x), group=a, B=50) 
resampGetArgument(boot, "group")