R/xyplot.R

In mice: Multivariate Imputation by Chained Equations

#' Scatterplot of observed and imputed data
#'
#' Plotting methods for imputed data using \pkg{lattice}.
#' \code{xyplot()} produces a conditional scatterplots. The function
#' automatically separates the observed (blue) and imputed (red) data. The
#' function extends the usual features of \pkg{lattice}.
#'
#' The argument \code{na.groups} may be used to specify (combinations of)
#' missingness in any of the variables. The argument \code{groups} can be used
#' to specify groups based on the variable values themselves. Only one of both
#' may be active at the same time. When both are specified, \code{na.groups}
#' takes precedence over \code{groups}.
#'
#' Use the \code{subset} and \code{na.groups} together to plots parts of the
#' data. For example, select the first imputed data set by by
#' \code{subset=.imp==1}.
#'
#' Graphical parameters like \code{col}, \code{pch} and \code{cex} can be
#' specified in the arguments list to alter the plotting symbols. If
#' \code{length(col)==2}, the color specification to define the observed and
#' missing groups. \code{col[1]} is the color of the 'observed' data,
#' \code{col[2]} is the color of the missing or imputed data. A convenient color
#' choice is \code{col=mdc(1:2)}, a transparent blue color for the observed
#' data, and a transparent red color for the imputed data. A good choice is
#' \code{col=mdc(1:2), pch=20, cex=1.5}. These choices can be set for the
#' duration of the session by running \code{mice.theme()}.
#'
#' @aliases xyplot
#' @param x A \code{mids} object, typically created by \code{mice()} or
#' \code{mice.mids()}.
#' @param data Formula that selects the data to be plotted.  This argument
#' follows the \pkg{lattice} rules for \emph{formulas}, describing the primary
#' variables (used for the per-panel display) and the optional conditioning
#' variables (which define the subsets plotted in different panels) to be used
#' in the plot.
#'
#' The formula is evaluated on the complete data set in the \code{long} form.
#' Legal variable names for the formula include \code{names(x$data)} plus the
#' two administrative factors \code{.imp} and \code{.id}.
#'
#' \bold{Extended formula interface:} The primary variable terms (both the LHS
#' \code{y} and RHS \code{x}) may consist of multiple terms separated by a
#' \sQuote{+} sign, e.g., \code{y1 + y2 ~ x | a * b}.  This formula would be
#' taken to mean that the user wants to plot both \code{y1 ~ x | a * b} and
#' \code{y2 ~ x | a * b}, but with the \code{y1 ~ x} and \code{y2 ~ x} in
#' \emph{separate panels}. This behavior differs from standard \pkg{lattice}.
#' \emph{Only combine terms of the same type}, i.e. only factors or only
#' numerical variables. Mixing numerical and categorical data occasionally
#' produces odds labeling of vertical axis.
#'
#' @param na.groups An expression evaluating to a logical vector indicating
#' which two groups are distinguished (e.g. using different colors) in the
#' display. The environment in which this expression is evaluated in the
#' response indicator \code{is.na(x$data)}.
#'
#' The default \code{na.group = NULL} contrasts the observed and missing data
#' in the LHS \code{y} variable of the display, i.e. groups created by
#' \code{is.na(y)}. The expression \code{y} creates the groups according to
#' \code{is.na(y)}. The expression \code{y1 & y2} creates groups by
#' \code{is.na(y1) & is.na(y2)}, and \code{y1 | y2} creates groups as
#' \code{is.na(y1) | is.na(y2)}, and so on.
#' @param groups This is the usual \code{groups} arguments in \pkg{lattice}. It
#' differs from \code{na.groups} because it evaluates in the completed data
#' \code{data.frame(complete(x, "long", inc=TRUE))} (as usual), whereas
#' \code{na.groups} evaluates in the response indicator. See
#' \code{\link{xyplot}} for more details. When both \code{na.groups} and
#' \code{groups} are specified, \code{na.groups} takes precedence, and
#' \code{groups} is ignored.
#' @param theme A named list containing the graphical parameters. The default
#' function \code{mice.theme} produces a short list of default colors, line
#' width, and so on. The extensive list may be obtained from
#' \code{trellis.par.get()}. Global graphical parameters like \code{col} or
#' \code{cex} in high-level calls are still honored, so first experiment with
#' the global parameters. Many setting consists of a pair. For example,
#' \code{mice.theme} defines two symbol colors. The first is for the observed
#' data, the second for the imputed data. The theme settings only exist during
#' the call, and do not affect the trellis graphical parameters.
#' @param as.table See \code{\link[lattice:xyplot]{xyplot}}.
#' @param outer See \code{\link[lattice:xyplot]{xyplot}}.
#' @param allow.multiple See \code{\link[lattice:xyplot]{xyplot}}.
#' @param drop.unused.levels See \code{\link[lattice:xyplot]{xyplot}}.
#' @param subscripts See \code{\link[lattice:xyplot]{xyplot}}.
#' @param subset See \code{\link[lattice:xyplot]{xyplot}}.
#' @param \dots Further arguments, usually not directly processed by the
#' high-level functions documented here, but instead passed on to other
#' functions.
#' @return The high-level functions documented here, as well as other high-level
#' Lattice functions, return an object of class \code{"trellis"}.  The
#' \code{\link[lattice:update.trellis]{update}} method can be used to
#' subsequently update components of the object, and the
#' \code{\link[lattice:print.trellis]{print}} method (usually called by default)
#' will plot it on an appropriate plotting device.
#' @note The first two arguments (\code{x} and \code{data}) are reversed
#' compared to the standard Trellis syntax implemented in \pkg{lattice}. This
#' reversal was necessary in order to benefit from automatic method dispatch.
#'
#' In \pkg{mice} the argument \code{x} is always a \code{mids} object, whereas
#' in \pkg{lattice} the argument \code{x} is always a formula.
#'
#' In \pkg{mice} the argument \code{data} is always a formula object, whereas in
#' \pkg{lattice} the argument \code{data} is usually a data frame.
#'
#' All other arguments have identical interpretation.
#'
#' @author Stef van Buuren
#' @seealso \code{\link{mice}}, \code{\link{stripplot}}, \code{\link{densityplot}},
#' \code{\link{bwplot}}, \code{\link{lattice}} for an overview of the
#' package, as well as \code{\link[lattice:xyplot]{xyplot}},
#' \code{\link[lattice:panel.xyplot]{panel.xyplot}},
#' \code{\link[lattice:print.trellis]{print.trellis}},
#' \code{\link[lattice:trellis.par.get]{trellis.par.set}}
#' @references Sarkar, Deepayan (2008) \emph{Lattice: Multivariate Data
#' Visualization with R}, Springer.
#'
#' van Buuren S and Groothuis-Oudshoorn K (2011). \code{mice}: Multivariate
#' Imputation by Chained Equations in \code{R}. \emph{Journal of Statistical
#' Software}, \bold{45}(3), 1-67. \doi{10.18637/jss.v045.i03}
#' @keywords hplot
#' @examples
#' imp <- mice(boys, maxit = 1)
#'
#' # xyplot: scatterplot by imputation number
#' # observe the erroneous outlying imputed values
#' # (caused by imputing hgt from bmi)
#' xyplot(imp, hgt ~ age | .imp, pch = c(1, 20), cex = c(1, 1.5))
#'
#' # same, but label with missingness of wgt (four cases)
#' xyplot(imp, hgt ~ age | .imp, na.group = wgt, pch = c(1, 20), cex = c(1, 1.5))
#' @export
xyplot.mids <- function(x,
                        data,
                        na.groups = NULL,
                        groups = NULL,
                        as.table = TRUE,
                        theme = mice.theme(),
                        allow.multiple = TRUE,
                        outer = TRUE,
                        drop.unused.levels = lattice::lattice.getOption("drop.unused.levels"),
                        ...,
                        subscripts = TRUE,
                        subset = TRUE) {
  call <- match.call()
  if (!is.mids(x)) stop("Argument 'x' must be a 'mids' object")
  if (missing(data)) stop("Missing formula")
  formula <- data

  ## unpack data and response indicator
  cd <- data.frame(complete(x, "long", include = TRUE))
  r <- as.data.frame(is.na(x$data))

  ## evaluate na.group in response indicator
  nagp <- eval(expr = substitute(na.groups), envir = r, enclos = parent.frame())
  if (is.expression(nagp)) nagp <- eval(expr = nagp, envir = r, enclos = parent.frame())

  ## evaluate groups in imputed data
  ngp <- eval(expr = substitute(groups), envir = cd, enclos = parent.frame())
  if (is.expression(ngp)) ngp <- eval(expr = ngp, envir = cd, enclos = parent.frame())
  groups <- ngp

  ## evaluate subset in imputed data
  ss <- eval(expr = substitute(subset), envir = cd, enclos = parent.frame())
  if (is.expression(ss)) ss <- eval(expr = ss, envir = cd, enclos = parent.frame())
  subset <- ss

  ## evaluate further arguments before parsing
  dots <- list(...)
  args <- list(
    allow.multiple = allow.multiple,
    outer = outer,
    drop.unused.levels = drop.unused.levels,
    subscripts = subscripts,
    as.table = as.table
  )

  ## determine the y-variables
  form <- lattice::latticeParseFormula(
    model = formula, data = cd, subset = subset,
    groups = groups, multiple = allow.multiple,
    outer = outer, subscripts = TRUE,
    drop = drop.unused.levels
  )
  ynames <- unlist(lapply(strsplit(form$left.name, " \\+ "), rm.whitespace))

  ## calculate selection vector gp
  nona <- is.null(call$na.groups)
  if (!is.null(call$groups) && nona) {
    gp <- call$groups
  } else {
    if (nona) {
      na.df <- r[, ynames, drop = FALSE]
      gp <- unlist(lapply(na.df, rep.int, x$m + 1))
    } else {
      gp <- rep.int(nagp, length(ynames) * (x$m + 1))
    }
  }

  ## change axis defaults of extended formula interface
  if (is.null(call$ylab)) {
    args$ylab <- ""
    if (length(ynames) == 1) args$ylab <- ynames
  }
  if (is.null(call$scales)) {
    args$scales <- list()
    if (length(ynames) > 1) {
      args$scales <- list(
        x = list(relation = "free"),
        y = list(relation = "free")
      )
    }
  }

  ## ready
  args <- c(
    x = formula, data = list(cd),
    groups = list(gp),
    args, dots, subset = call$subset
  )

  ## go
  tp <- do.call("xyplot", args)
  update(tp, par.settings = theme)
}