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add doc page for data.table options
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‎man/data.table-options.Rd‎

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\name{data.table-options}
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\alias{data.table-options}
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\alias{data.table.options}
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\title{Global Options for the data.table Package}
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\description{
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The data.table package uses a number of global options to control its
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behavior. These are regular R options that can be set with options()
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and retrieved with getOption().
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This page provides a comprehensive, up-to-date list of all user-configurable
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options.
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}
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\usage{
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\preformatted{
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# Get the current value of an option
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getOption("datatable.print.topn")
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# Set a new value for an option
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options(datatable.print.topn = 10)
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}
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}
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\section{Printing Options}{
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\details{
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\describe{
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\item{\code{datatable.print.topn}}{An integer. When a data.table is printed,
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only the first topn and last topn rows are displayed. This prevents
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cluttering the console for large tables.
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Default: \code{5L}. See \code{\link{print.data.table}}.}
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\item{\code{datatable.print.nrows}}{An integer. The total number of rows
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to print before the topn logic is triggered.
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Default: \code{100L}.}
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\item{\code{datatable.print.class}}{A logical. If \code{TRUE}, the class of
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each column is printed below the column name.
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Default: \code{FALSE}.}
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\item{\code{datatable.print.keys}}{A logical. If \code{TRUE}, the table's
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keys are printed above the data.
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Default: \code{FALSE}.}
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\item{\code{datatable.print.trunc.cols}}{A logical. If \code{TRUE} and a
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table has more columns than fit on the screen, it truncates the middle
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columns for printing (e.g., a, b, ..., z). If \code{FALSE}, it wraps
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the columns to the next line.
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Default: \code{FALSE}.}
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\item{\code{datatable.prettyprint.char}}{An integer. The maximum number of
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characters to display in a character column cell before truncating
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with ....
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Default: \code{100L}.}
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}
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}
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\section{File I/O Options (fread and fwrite)}{
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\describe{
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\item{\code{datatable.fread.input.cmd.message}}{A logical. If \code{TRUE},
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fread will print the shell command it is using when the input is a
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command (e.g., fread("grep ...")).
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Default: \code{TRUE}. See \code{\link{fread}}.}
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\item{\code{datatable.fread.datatable}}{A logical. If \code{TRUE}, fread
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returns a data.table. If FALSE, it returns a data.frame.
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Default: \code{TRUE}.}
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\item{\code{datatable.integer64}}{A character string. Controls how fread
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handles 64-bit integers. Can be "integer64" (requires bit64 package),
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"double" (loses precision), or "character" (reads as text).
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Default: \code{"integer64"}.}
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\item{\code{datatable.logical01}}{A logical. If \code{TRUE}, fread will
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interpret columns containing only 0 and 1 as logical FALSE/TRUE.
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Default: \code{FALSE}.}
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\item{\code{datatable.showProgress}}{An integer or logical. Controls whether
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long-running operations like fread display a progress bar. Default
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is \code{interactive()}, showing it only in interactive R sessions.}
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}
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}
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\section{Join and Subset Options}{
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\describe{
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\item{\code{datatable.allow.cartesian}}{A logical. A safety feature to prevent
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accidental memory-exploding joins. If FALSE (default), a join is not
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allowed if the result would be more rows than max(nrow(x), nrow(i)),
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which occurs when a row in i matches more than one row in x.
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Default: \code{FALSE}. See \code{\link{data.table}}.}
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\item{\code{datatable.nomatch}}{Controls the behavior of non-matching rows in
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a join. The default is NA, which returns NA for columns of x when a
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row in i has no match. Can be set to 0L to drop non-matching rows,
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behaving like an inner join.
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Default: \code{NA}.}
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}
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}
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\section{Performance and Indexing Options}{
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\describe{
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\item{\code{datatable.auto.index}}{A logical. If \code{TRUE}, data.table
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automatically creates a secondary index on-the-fly the first time a column
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is used in a query (e.g., DT[col == 'value']). This dramatically
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speeds up all subsequent queries on that same column.
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Default: \code{TRUE}.}
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\item{\code{datatable.use.index}}{A logical. A global switch to control
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whether existing indices are used for subsetting.
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Default: \code{TRUE}.}
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\item{\code{datatable.optimize}}{An integer controlling the GForce query
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optimization engine. Set to Inf to enable all possible optimizations,
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which data.table does by default. See \code{\link{datatable.optimize}}.
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Default: \code{Inf}.}
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\item{\code{datatable.alloccol}}{An integer. data.table pre-allocates
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memory for a certain number of columns when first created. This option
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controls the length of this pre-allocation, improving performance when
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adding many columns via :=. See \code{\link{alloc.col}}.
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Default: \code{1024L}.}
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}
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}
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\section{Development and Verbosity Options}{
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\describe{
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\item{\code{datatable.verbose}}{A logical. If \code{TRUE}, data.table will
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print detailed, step-by-step diagnostic information as it processes a
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query. Extremely useful for debugging and performance tuning.
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Default: \code{FALSE}.}
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\item{\code{datatable.pedantic}}{A logical. If \code{TRUE}, data.table
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enters a "pedantic" mode, issuing helpful warnings for situations that
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are not technically errors but might be unintentional (e.g., when a
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variable in j is found in the global environment instead of inside the
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data.table).
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Default: \code{FALSE}.}
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\item{\code{datatable.dfdispatchwarn}}{A logical. If \code{TRUE}, warns
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when a generic function from another package (e.g., dplyr::filter) is
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applied to a data.table. This can be a useful reminder that you are not
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using data.table's optimized methods.
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Default: \code{TRUE}.}
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}
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}
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\section{Internal Strings (Not User Options)}{
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\describe{
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\item{The following strings are not options to be set by users.}{They are
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included here to assist developers searching the source code. They are typically
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parts of URLs found in code comments or documentation.
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\itemize{
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\item \code{datatable.com}
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\item \code{datatable.github.io}
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\item \code{datatable.gitlab.io}
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}
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}
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}
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}
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}
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\seealso{
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\code{\link{options}},
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\code{\link{getOption}},
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\code{\link{data.table}}
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}
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\keyword{data}
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\keyword{utilities}

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