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.
row.names(x)
row.names(x) <- valueobject of class "data.frame", or any other class for
which a method has been defined.
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’.
row.names returns a character vector.
row.names<- returns a data frame with the row names changed.
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’.
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.
.row_names_info for the internal representations.