dttable() describes a data.table rather than cross tabulating it. Given a
single data.table it reports one row per column – the name, the number of
unique values, and the values themselves – and returns that description as a
data.table with the columns Variable, N_unique and Unique_value.
Arguments
- ...
The vectors to tabulate, as in
base::table(), or a singledata.tableto describe.
Value
For a single data.table, a data.table with the columns
Variable, N_unique and Unique_value, returned invisibly. For
anything else, whatever base::table() returns.
Details
dttable() is a function of its own: it does not mask base::table(), and
loading dtlog leaves table() exactly as it was. Every call that is not a
single data.table is handed to base::table() unchanged, so
dttable(dt$sex, dt$death), dttable(x, useNA = "ifany") and
dttable(as.data.frame(dt)) return what base::table() returns. Describing
a single data.table is the only thing dttable() adds.
A column with 20 or more unique values is reported as possibly continuous
rather than listed; the option dtlog.table_max_unique moves that point,
and Inf lists every column however many values it holds. A list column is
reported as such, and a list of values longer than 80 characters is
truncated.
The values are listed in the order the column sorts in: numbers ascending,
characters alphabetically, dates and times chronologically, factors and
ordered factors by their levels, FALSE before TRUE. Each value is
written the way its own class writes it, so an ITime is listed as
09:00:00 rather than as the seconds it is stored as. A type that cannot be
sorted keeps the order its values appear in.
Missing values are listed and counted like any other value: NA (including
NA as a level of a factor) appears as Missing, NaN as NaN, and both
are counted in N_unique. They sort last, so a column that has any ends
with Missing. An empty string is a value of its own, not a missing one.
The description goes through the same output as every other dtlog
message, so it obeys dtlog.display, is silenced by dtlog_pause(), and is
written to the transcript opened by dt_log().
See also
dtlog_summary() for the size and key of a table alone.
Examples
dttable(data.table::data.table(a = 1:3, b = c("x", "y", "x")))
#> dttable: 3 rows and 2 columns
#> Variable N_unique Unique_value
#> a 3 1; 2; 3
#> b 2 x; y
dttable(c("a", "b", "a"))
#>
#> a b
#> 2 1