Combine R Objects by Rows or Columns

Description

Take a sequence of vector, matrix or data frames arguments and combine by columns or rows, respectively. These are generic functions with methods for other R classes.

Usage

cbind(..., deparse.level = 1)
rbind(..., deparse.level = 1)

Arguments

Details

The functions cbind and rbind are generic, with methods for data frames. The data frame method will be used if an argument is a data frame and the rest are vectors or matrices. There can be other methods; in particular, there is one for time series objects.

In the matrix case, all the vectors/matrices must be atomic or lists (e.g. not expressions).

Data frames can be cbind-ed with matrices, in which case each matrix forms a single column in the result, unlike calling data.frame.

The rbind data frame method takes the classes of the columns from the first data frame. Factors have their levels expanded as necessary (in the order of the levels of the levelsets of the factors encountered) and the result is an ordered factor if and only if all the components were ordered factors. (The last point differs from S-PLUS.)

If there are several matrix arguments, they must all have the same number of columns (or rows) and this will be the number of columns (or rows) of the result. If all the arguments are vectors, the number of columns (rows) in the result is equal to the length of the longest vector. Values in shorter arguments are recycled to achieve this length (with a warning if they are recycled only fractionally).

When the arguments consist of a mix of matrices and vectors the number of columns (rows) of the result is determined by the number of columns (rows) of the matrix arguments. Any vectors have their values recycled or subsetted to achieve this length.

For cbind (rbind), vectors of zero length (including NULL) are ignored unless the result would have zero rows (columns), for S compatibility. (Zero-extent matrices do not occur in S3 and are not ignored in R.)

Value

A matrix or data frame combining the ... arguments column-wise or row-wise.
For cbind (rbind) the column (row) names are taken from the names of the arguments, or where those are not supplied by deparsing the expressions given (if that gives a sensible name). The names will depend on whether data frames are included: see the examples.

Note

The method dispatching is not done via UseMethod(), but by C-internal dispatching. Therefore, there is no need for, e.g., rbind.default.

The dispatch algorithm is described in the source file (‘.../src/main/bind.c’) as

1. For each argument we get the list of possible class memberships from the class attribute.
2. We inspect each class in turn to see if there is an an applicable method.
3. If we find an applicable method we make sure that it is identical to any method determined for prior arguments. If it is identical, we proceed, otherwise we immediately drop through to the default code.

If you want to combine other objects with data frames, it may be necessary to coerce them to data frames first. (Note that this algorithm can result in calling the data frame method if the arguments are all either data frames or vectors, and this will result in the coercion of character vectors to factors.)

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also

c to combine vectors (and lists) as vectors, data.frame to combine vectors and matrices as a data frame.

Examples

m <- cbind(1, 1:7) # the '1' (= shorter vector) is recycled
m
m <- cbind(m, 8:14)[, c(1, 3, 2)] # insert a column 
m
cbind(1:7, diag(3))# vector is subset -> warning

cbind(0, rbind(1, 1:3))
cbind(I=0, X=rbind(a=1, b=1:3))  # use some names
xx <- data.frame(I=rep(0,2))
cbind(xx, X=rbind(a=1, b=1:3))   # named differently

cbind(0, matrix(1, nrow=0, ncol=4))#> Warning (making sense)
dim(cbind(0, matrix(1, nrow=2, ncol=0)))#-> 2 x 1