| split {base} | R Documentation |
Divide into Groups
Description
split divides the data in the vector x into the groups
defined by f. The replacement forms replace values
corresponding to such a division. unsplit reverses the effect of
split.
Usage
split(x, f, drop = FALSE, ...)
split(x, f, drop = FALSE, ...) <- value
unsplit(value, f, drop = FALSE)
Arguments
x |
vector or data frame containing values to be divided into groups. |
f |
a “factor” in the sense that |
drop |
logical indicating if levels that do not occur should be dropped
(if |
value |
a list of vectors or data frames compatible with a
splitting of |
... |
further potential arguments passed to methods. |
Details
split and split<- are generic functions with default and
data.frame methods.
f is recycled as necessary and if the length of x is not
a multiple of the length of f a warning is printed.
unsplit works only with lists of vectors. The data frame
method can also be used to split a matrix into a list of matrices,
and the replacement form likewise, provided they are invoked
explicitly.
Any missing values in f are dropped together with the
corresponding values of x.
Value
The value returned from split is a list of vectors containing
the values for the groups. The components of the list are named by
the used factor levels given by f. (If f is
longer than x then some of the components will be of zero length.)
The replacement forms return their right hand side. unsplit
returns a vector for which split(x, f) equals value
References
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth \& Brooks/Cole.
See Also
cut
Examples
require(stats)
n <- 10; nn <- 100
g <- factor(round(n * runif(n * nn)))
x <- rnorm(n * nn) + sqrt(as.numeric(g))
xg <- split(x, g)
boxplot(xg, col = "lavender", notch = TRUE, varwidth = TRUE)
sapply(xg, length)
sapply(xg, mean)
## Calculate z-scores by group
z <- unsplit(lapply(split(x, g), scale), g)
tapply(z, g, mean)
# or
z <- x
split(z, g) <- lapply(split(x, g), scale)
tapply(z, g, sd)
## Split a matrix into a list by columns
ma <- cbind(x = 1:10, y = (-4:5)^2)
split(ma, col(ma))
split(1:10, 1:2)