data.table (version 1.4.1)

data.table: Enhanced data.frame

Description

Same internal structure as data.frame (i.e. list of vectors) but fast subset, fast merge, and fast grouping.

Usage

data.table(..., keep.rownames=FALSE, check.names=TRUE, key=NULL)

Arguments

...

Just as ...in data.frame. These arguments are of either the form value or tag = value. Column names are created based on the tag (if present) or the deparsed argument itself.

The data.table can be f

keep.rownames

If ...is a matrix or data.frame, TRUE will retain the rownames of that object into a column 'rn'. If the matrix or data.frame already has a column called 'rn' it will be renamed 'rn.1' via make.names.

check.names

Just as check.names in data.frame(). For example this replaces spaces in column names with period and ensures column names are valid Robject names.

key

Character vector of length 1 containing one or more column names separated by comma which is passed to setkey

Value

• A data.table.

Details

data.table creates a data.table from its arguments just as data.frame does. DT() is an alias for data.table() and is often used instead of as.data.table().

A data.table is a list of vectors, just like a data.frame, however :

1. itneverhas rownames. Instead it may have an optionalkeyof one or more columns usingsetkey. This key can be used for row indexing instead of rownames.
2. when the data.table has over 20 rows the print method displays column names at the bottom as well as at the top to save scrolling up at the console.
3. character vectors may be passed in but they are automatically converted to factor. A data.table does not allow character columns for time and space reasons.
4. howeverthe main differenceis enhanced functionality in[.data.tablewhere most documentation for this package lives.

Several methods are provided for data tables, including is.na, na.omit, t, and others.

See Also

data.frame, tables, setkey, [.data.table

Examples

DF = data.frame(a=1:5, b=letters[1:5])
DT = data.table(a=1:5, b=letters[1:5])
identical(as.data.table(DF), DT)
identical(data.table(DF), DT)
identical(dim(DT),dim(DF))
identical(DF$a, DT$a)
DT
tables()
identical(data.table(DT,DT), cbind(DT,DT))
DT2=rbind(DT,DT)
DT3 = data.table(A=DT, B=DT, key="A.b")
tables()
test.data.table()
example("[.data.table")

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