row.names
Get and Set Row Names for Data Frames
All data frames have a row names attribute, a character vector of length the number of rows with no duplicates nor missing values.
For convenience, these are generic functions for which users can write
other methods, and there are default methods for arrays. The
description here is for the data.frame
method.
`.rowNamesDF<-`
is a (non-generic replacement) function to set
row names for data frames, with extra argument make.names
.
This function only exists as workaround as we cannot easily change the
row.names<-
generic without breaking legacy code in existing packages.
Usage
row.names(x)
row.names(x) <- value
.rowNamesDF(x, make.names=FALSE) <- value
Arguments
- x
object of class
"data.frame"
, or any other class for which a method has been defined.- make.names
logical
, i.e., one ofFALSE, NA, TRUE
, indicating what should happen if the specified row names, i.e.,value
, are invalid, e.g., duplicated orNA
. The default (is back compatible),FALSE
, will signal an error, whereNA
will “automatic” row names andTRUE
will callmake.names(value, unique=TRUE)
for constructing valid names.- value
an object to be coerced to character unless an integer vector. It should have (after coercion) the same length as the number of rows of
x
with no duplicated nor missing values.NULL
is also allowed: see ‘Details’.
Details
A data frame has (by definition) a vector of row names which has length the number of rows in the data frame, and contains neither missing nor duplicated values. Where a row names sequence has been added by the software to meet this requirement, they are regarded as ‘automatic’.
Row names are currently allowed to be integer or character, but
for backwards compatibility (with R <= 2.4.0) row.names
will
always return a character vector. (Use attr(x, "row.names")
if
you need to retrieve an integer-valued set of row names.)
Using NULL
for the value resets the row names to
seq_len(nrow(x))
, regarded as ‘automatic’.
Value
row.names
returns a character vector.
row.names<-
returns a data frame with the row names changed.
Note
row.names
is similar to rownames
for arrays, and
it has a method that calls rownames
for an array argument.
Row names of the form 1:n
for n > 2
are stored
internally in a compact form, which might be seen from C code or by
deparsing but never via row.names
or
attr(x, "row.names")
. Additionally, some names of this
sort are marked as ‘automatic’ and handled differently by
as.matrix
and data.matrix
(and potentially
other functions). (All zero-row data frames are regarded as having
automatic row.names.)
References
Chambers, J. M. (1992) Data for models. Chapter 3 of Statistical Models in S eds J. M. Chambers and T. J. Hastie, Wadsworth & Brooks/Cole.
See Also
.row_names_info
for the internal representations.