naresid
Adjust for Missing Values
Description
Use missing value information to adjust residuals and predictions.
Usage
naresid(omit, x, ...)
## Default S3 method:
naresid(omit, x, ...)
## S3 method for class 'exclude':
naresid(omit, x, ...)
## S3 method for class 'NULL':
naresid(omit, x, ...)
napredict(omit, x, ...)
## Default S3 method:
napredict(omit, x, ...)
## S3 method for class 'exclude':
napredict(omit, x, ...)
## S3 method for class 'NULL':
napredict(omit, x, ...)
Arguments
| omit |
an object produced by an na.action function such as na.exclude. Typically
this is the "na.action" component of a model object for which an na.action is
specified.
|
| x |
a vector or matrix to adjust based upon the missing
value information. Typically this is the residuals, fitted values, or
predictions for the subset of data left after removing rows based on the
na.action.
|
| ... |
additional arguments to be passed to or from future methods.
|
Details
Currently the only method that does anything is for na.exclude. In this
case, na.exclude returns a data.frame with rows containing missing values
removed and the numbers of these rows stored in an na.action attribute of
the data frame. Then the naresid function takes this attribute and the
residuals for the subset data frame and uses the information on the removed rows
to return a vector of the same length as the original data. That
is, this function pads with NAs to return a vector of residuals corresponding
to the original data.
Note that for na.action functions for which no naresid method has been
written, the generic naresid.default is called. This just returns the
specified x unmodified.
For a model to use this system,
the modeling function must take the na.action information produced
by model.frame and place it on the model object.
The following code from lm demonstrates this:
if(!is.null(attr(m, "na.action")))
fit$na.action <- attr(m, "na.action")
For a function such as residuals.lm to return the modified
residuals, it must call naresid before returning its result.
The convention is to use:
resids <- naresid(object$na.action, rawResids)
where object is the fitted model and rawResids is the residuals for the subset of data used in the model.
An ambitious user could write his own function na.myway with
corresponding functions naresid.myway and napredict.myway.
The developer can expect naresid to be applied to the results of residuals.
The function napredict is currently applied only to the results
of predict when no new data is specified.
NOTE: For na.exclude, both of these functions do the same thing.
The separate functions for naresid and napredict are available to support
more general functionality than is currently implemented.
Value
returns a vector or matrix (with the same number of columns as the input)
adjusted based upon the na.action information.
See Also
Examples
d <- data.frame(x=c(1,2,NA,4), y=c(11,NA,13,14))
dex <- na.exclude(d)
naresid(attr(dex, "na.action"), dex$y - dex$x)