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% File src/library/base/man/warnings.Rd
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% File src/library/base/man/warnings.Rd
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% Part of the R package, https://www.R-project.org
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% Part of the R package, https://www.R-project.org
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% Copyright 1995-2016 R Core Team
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% Copyright 1995-2017 R Core Team
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% Distributed under GPL 2 or later
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% Distributed under GPL 2 or later
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\name{warnings}
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\name{warnings}
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\title{Print Warning Messages}
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\title{Print Warning Messages}
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\alias{warnings}
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\alias{warnings}%%--> ../R/warnings.R
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\alias{last.warning}
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\alias{last.warning}
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\alias{print.warnings}
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\alias{print.warnings}
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\alias{[.warnings}
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\alias{[.warnings}
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\alias{c.warnings}
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\alias{c.warnings}
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\alias{duplicated.warnings}
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\alias{duplicated.warnings}
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\alias{unique.warnings}
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\alias{unique.warnings}
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\alias{summary.warnings}
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\alias{print.summary.warnings}
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\description{
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\description{
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  \code{warnings} and its \code{print} method print the
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  \code{warnings} and its \code{print} method print the
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  variable \code{last.warning} in a pleasing form.
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  variable \code{last.warning} in a pleasing form.
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}
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}
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\usage{
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\usage{
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warnings(\dots)
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warnings(\dots)
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\S3method{summary}{warnings}(object, \dots)
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\S3method{print}{warnings}(x, tags,
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      header = ngettext(n, "Warning message:\n", "Warning messages:\n"),
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      \dots)
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\S3method{print}{summary.warnings}(x, \dots)
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}
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}
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\arguments{
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\arguments{
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  \item{\dots}{arguments to be passed to \code{\link{cat}}.}
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  \item{\dots}{arguments to be passed to \code{\link{cat}} (for
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    \code{warnings()}).}
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  \item{object}{a \code{"warnings"} object as returned by
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    \code{warnings()}.}
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  \item{x}{a \code{"warnings"} or \code{"summary.warnings"} object.}
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  \item{tags}{if not \code{\link{missing}}, a \code{\link{character}}
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    vector of the same \code{\link{length}} as \code{x}, to \dQuote{label}
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    the messages.  Defaults to \code{paste0(seq_len(n), ": ")} for
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    \eqn{n \ge 2}{n >= 2} where \code{n <- length(x)}.}
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  \item{header}{a character string \code{\link{cat}()}ed before the
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      messages are printed.}
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}
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}
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\references{
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\references{
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  Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
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  Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
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  \emph{The New S Language}.
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  \emph{The New S Language}.
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  Wadsworth & Brooks/Cole.
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  Wadsworth & Brooks/Cole.
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  visible, and this is subject to change.
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  visible, and this is subject to change.
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}
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}
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\seealso{
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\seealso{
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  \code{\link{warning}}.
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  \code{\link{warning}}.
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}
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}
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\value{an object of S3 class \code{"warnings"}, basically a named
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\value{\code{warnings()} returns an object of S3 class \code{"warnings"}, basically a named
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  \code{\link{list}}.
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  \code{\link{list}}.
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  \code{summary(<warnings>)} returns a \code{"summary.warnings"}
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  object which is basically the \code{\link{list}} of unique warnings
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  (\code{unique(object)}) with a \code{"counts"} attribute, somewhat
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  experimentally.
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}
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}
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\examples{
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\examples{
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## NB this example is intended to be pasted in,
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## NB this example is intended to be pasted in,
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##    rather than run by example()
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##    rather than run by example()
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ow <- options("warn")
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ow <- options("warn")
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for(w in -1:1) {
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for(w in -1:1) {
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   options(warn = w); cat("\n warn =", w, "\n")
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   options(warn = w); cat("\n warn =", w, "\n")
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   for(i in 1:3) { cat(i,"..\n"); m <- matrix(1:7, 3,4) }
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   for(i in 1:3) { cat(i,"..\n"); m <- matrix(1:7, 3,4) }
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   cat("--=--=--\n")
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}
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}
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warnings()
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## at the end prints all three warnings, from the 'option(warn = 0)' above
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options(ow) # reset
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options(ow) # reset to previous, typically 'warn = 0'
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tail(warnings(), 2) # see the last two warnings only (via '[' method)
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tail(warnings(), 2) # see the last two warnings only (via '[' method)
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## Often the most useful way to look at many warnings:
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summary(warnings())
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\dontshow{
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\dontshow{
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ww <- warnings()
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ww <- warnings()
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uw <- unique(ww)
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uw <- unique(ww)
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sw <- summary(ww)
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stopifnot(identical(c(ww[1], ww[3]), ww[c(1, 3)]),
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stopifnot(identical(c(ww[1], ww[3]), ww[c(1, 3)]),
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          length(uw) == 1, nchar(names(uw)) > 10)
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          length(uw) == 1, nchar(names(uw)) > 10,
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          length(sw) == 1, attr(sw, "counts") == 3)
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}
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}
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op <- options(nwarnings = 10000) ## <- get "full statistics"
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x <- 1:36; for(n in 1:13) for(m in 1:12) A <- matrix(x, n,m) # There were 105 warnings ...
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summary(warnings())
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options(op) # revert to previous (keeping 50 messages by default)
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}
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}
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\keyword{programming}
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\keyword{programming}
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\keyword{error}
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\keyword{error}