print.data.table {data.table}

data.table Printing Options

Description

print.data.table extends the functionalities of print.data.frame.

Key enhancements include automatic output compression of many observations and concise column-wise class summary.

format_col and format_list_item generics provide flexibility for end-users to define custom printing methods for generic classes.

Usage

  ## S3 method for class 'data.table'
print(x,
    topn=getOption("datatable.print.topn"),             # default: 5
    nrows=getOption("datatable.print.nrows"),           # default: 100
    class=getOption("datatable.print.class"),           # default: TRUE
    row.names=getOption("datatable.print.rownames"),    # default: TRUE
    col.names=getOption("datatable.print.colnames"),    # default: "auto"
    print.keys=getOption("datatable.print.keys"),       # default: TRUE
    trunc.cols=getOption("datatable.print.trunc.cols"), # default: FALSE
    quote=FALSE,
    timezone=FALSE, ...)

  format_col(x, ...)
  ## Default S3 method:
format_col(x, ...)
  ## S3 method for class 'POSIXct'
format_col(x, ..., timezone=FALSE)
  ## S3 method for class 'expression'
format_col(x, ...)

  format_list_item(x, ...)
  ## Default S3 method:
format_list_item(x, ...)

Arguments

x

A data.table.

topn

The number of rows to be printed from the beginning and end of tables with more than nrows rows.

nrows

The number of rows which will be printed before truncation is enforced.

class

If TRUE, the resulting output will include above each column its storage class (or a self-evident abbreviation thereof).

row.names

If TRUE, row indices will be printed alongside x.

col.names

One of three flavours for controlling the display of column names in output. "auto" includes column names above the data, as well as below the table if nrow(x) > 20. "top" excludes this lower register when applicable, and "none" suppresses column names altogether (as well as column classes if class = TRUE.

print.keys

If TRUE, any key and/or index currently assigned to x will be printed prior to the preview of the data.

trunc.cols

If TRUE, only the columns that can be printed in the console without wrapping the columns to new lines will be printed (similar to tibbles).

quote

If TRUE, all output will appear in quotes, as in print.default.

timezone

If TRUE, time columns of class POSIXct or POSIXlt will be printed with their timezones (if attribute is available).

...

Other arguments ultimately passed to format.

Details

By default, with an eye to the typically large number of observations in a data.table, only the beginning and end of the object are displayed (specifically, head(x, topn) and tail(x, topn) are displayed unless nrow(x) < nrows, in which case all rows will print).

format_col is applied at a column level; for example, format_col.POSIXct is used to tag the time zones of POSIXct columns. format_list_item is applied to the elements (rows) of list columns; see Examples. The default format_col method uses getS3method to test if a format method exists for the column, and if so uses it. Otherwise, the default format_list_item method uses the S3 format method (if one exists) for each item of a list column.

Value

print.data.table returns x invisibly.

format_col returns a length(x)-size character vector.

format_list_item returns a length-1 character scalar.

See Also

print.default

Examples

  #output compression
  DT <- data.table(a = 1:1000)
  print(DT, nrows = 100, topn = 4)

  #`quote` can be used to identify whitespace
  DT <- data.table(blanks = c(" 12", " 34"),
                   noblanks = c("12", "34"))
  print(DT, quote = TRUE)

  #`class` provides handy column type summaries at a glance
  DT <- data.table(a = vector("integer", 3),
                   b = vector("complex", 3),
                   c = as.IDate(paste0("2016-02-0", 1:3)))
  print(DT, class = TRUE)

  #`row.names` can be eliminated to save space
  DT <- data.table(a = 1:3)
  print(DT, row.names = FALSE)

  #`print.keys` can alert which columns are currently keys
  DT <- data.table(a=1:3, b=4:6, c=7:9, key="b,a")
  setindexv(DT, c("a", "b"))
  setindexv(DT, "a")
  print(DT, print.keys=TRUE)

  # `trunc.cols` will make it so only columns that fit in console will be printed
  #    with a message that states the variables not shown
  old_width = options("width" = 40)
  DT <- data.table(thing_11 = vector("integer", 3),
                   thing_21 = vector("complex", 3),
                   thing_31 = as.IDate(paste0("2016-02-0", 1:3)),
                   thing_41 = "aasdfasdfasdfasdfasdfasdfasdfasdfasdfasdf",
                   thing_51 = vector("integer", 3),
                   thing_61 = vector("complex", 3))
  print(DT, trunc.cols=TRUE)
  options(old_width)

  # Formatting customization
  format_col.complex = function(x, ...) sprintf('(%.1f, %.1fi)', Re(x), Im(x))
  x = data.table(z = c(1 + 3i, 2 - 1i, pi + 2.718i))
  print(x)

  iris = as.data.table(iris)
  iris_agg = iris[ , .(reg = list(lm(Sepal.Length ~ Petal.Length))), by = Species]
  format_list_item.lm = function(x, ...) sprintf('<lm:%s>', format(x$call$formula))
  print(iris_agg)