Global Options for the data.table Package

The data.table package uses a number of global options to control its behavior. These are regular R options that can be set with options() and retrieved with getOption(). For example:


    # Get the current value of an option
    getOption("datatable.print.topn")

    # Set a new value for an option
    options(datatable.print.topn = 10)

This page provides a comprehensive, up-to-date list of all user-configurable options. NB: If you're reading this on the web, make sure the version numbers match with what you have installed.

Printing Options

See print.data.table for a full description of printing data.tables.

datatable.print.topn: An integer, default 5L. When a data.table is printed, only the first topn and last topn rows are displayed.
datatable.print.nrows: An integer, default 100L. The total number of rows to print before the topn logic is triggered.
datatable.print.class: A logical, default FALSE. If TRUE, the class of each column is printed below its name.
datatable.print.keys: A logical, default FALSE. If TRUE, the table's keys are printed above the data.
datatable.show.indices: A logical, default TRUE. A synonym for datatable.print.keys for historical reasons.
datatable.print.trunc.cols: A logical, default FALSE. If TRUE and a table has more columns than fit on the screen, it truncates the middle columns.
datatable.prettyprint.char: An integer, default 100L. The maximum number of characters to display in a character column cell before truncating.
datatable.print.colnames: A logical, default TRUE. If TRUE, prints column names.
datatable.print.rownames: A logical, default TRUE. If TRUE, prints row numbers.

File I/O Options (fread and fwrite)

See fread and fwrite for a full description of data.table I/O.

datatable.fread.input.cmd.message: A logical, default TRUE. If TRUE, fread will print the shell command it is using when the input is a command (e.g., fread("grep ...")).
datatable.fread.datatable: A logical, default TRUE. If TRUE, fread returns a data.table. If FALSE, it returns a data.frame.
datatable.integer64: A character string, default "integer64". Controls how fread handles 64-bit integers. Can be "integer64", "double", or "character".
datatable.logical01: A logical, default FALSE. If TRUE, fread will interpret columns containing only 0 and 1 as logical.
datatable.keepLeadingZeros: A logical, default FALSE. If TRUE, fread preserves leading zeros in character columns by reading them as strings; otherwise they may be coerced to numeric.
datatable.logicalYN: A logical, default FALSE. If TRUE, fread will interpret "Y" and "N" as logical.
datatable.na.strings: A character vector, default "NA". Global default for strings that fread should interpret as NA.
datatable.fwrite.sep: A character string, default ",". The default separator used by fwrite.
datatable.showProgress: An integer or logical, default interactive(). Controls whether long-running operations like fread display a progress bar.

Join and Subset Options

datatable.allow.cartesian: A logical, default FALSE. Controls the default value of the allow.cartesian parameter; see data.table. If the value of this parameter is FALSE, an error is raised as a safeguard against an explosive Cartesian join.
datatable.join.many: A logical. Stub description to be embellished later in PR #4370.

Performance and Indexing Options

datatable.auto.index: A logical, default TRUE. If TRUE, data.table automatically creates a secondary index on-the-fly when a column is first used in a subset, speeding up all subsequent queries.
datatable.use.index: A logical, default TRUE. A global switch to control whether existing secondary indices are used for subsetting.
datatable.forder.auto.index: A logical, default TRUE. Similar to datatable.auto.index, but applies to ordering operations (forder).
datatable.optimize: A numeric, default Inf. Controls the GForce query optimization engine. The default enables all possible optimizations. See datatable.optimize.
datatable.alloccol: An integer, default 1024L. Controls the number of column slots to pre-allocate, improving performance when adding many columns. See alloc.col.
datatable.reuse.sorting: A logical, default TRUE. If TRUE, data.table can reuse the sorted order of a table in joins, improving performance.

Development and Verbosity Options

datatable.quiet: A logical, default FALSE. The master switch to suppress all data.table status messages, including the startup message.
datatable.verbose: A logical, default FALSE. If TRUE, data.table will print detailed diagnostic information as it processes a query.
datatable.enlist: Experimental feature. Default is NULL. If set to a function (e.g., list), the j expression can return a list, which will then be "enlisted" into columns in the result.

Back-compatibility Options

datatable.old.matrix.autoname: Logical, default TRUE. Governs how the output of expressions like data.table(x=1, cbind(1)) will be named. When TRUE, it will be named V1, otherwise it will be named V2.