cut {base}R Documentation

Convert Numeric to Factor

Description

cut divides the range of x into intervals and codes the values in x according to which interval they fall. The leftmost interval corresponds to level one, the next leftmost to level two and so on.

Usage

cut(x, ...)

## Default S3 method:
cut(x, breaks, labels = NULL,
    include.lowest = FALSE, right = TRUE, dig.lab = 3, ...)

Arguments

x a numeric vector which is to be converted to a factor by cutting.
breaks either a vector of cut points or number giving the number of intervals which x is to be cut into.
labels labels for the levels of the resulting category. By default, labels are constructed using "(a,b]" interval notation. If labels = FALSE, simple integer codes are returned instead of a factor.
include.lowest logical, indicating if an ‘x[i]’ equal to the lowest (or highest, for right = FALSE) ‘breaks’ value should be included.
right logical, indicating if the intervals should be closed on the right (and open on the left) or vice versa.
dig.lab integer which is used when labels are not given. It determines the number of digits used in formatting the break numbers.
... further arguments passed to or from other methods.

Details

If a labels parameter is specified, its values are used to name the factor levels. If none is specified, the factor level labels are constructed as "(b1, b2]", "(b2, b3]" etc. for right = TRUE and as "[b1, b2)", ... if right = FALSE. In this case, dig.lab indicates the minimum number of digits should be used in formatting the numbers b1, b2, .... A larger value (up to 12) will be used if needed to distinguish between any pair of endpoints: if this fails labels such as "Range3" will be used.

Value

A factor is returned, unless labels = FALSE which results in the mere integer level codes.

Note

Instead of table(cut(x, br)), hist(x, br, plot = FALSE) is more efficient and less memory hungry. Instead of cut(*, labels = FALSE), findInterval() is more efficient.

References

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

See Also

split for splitting a variable according to a group factor; factor, tabulate, table, findInterval().

Examples

Z <- rnorm(10000)
table(cut(Z, br = -6:6))
sum(table(cut(Z, br = -6:6, labels=FALSE)))
sum(   hist  (Z, br = -6:6, plot=FALSE)$counts)

cut(rep(1,5),4)#-- dummy
tx0 <- c(9, 4, 6, 5, 3, 10, 5, 3, 5)
x <- rep(0:8, tx0)
stopifnot(table(x) == tx0)

table( cut(x, b = 8))
table( cut(x, br = 3*(-2:5)))
table( cut(x, br = 3*(-2:5), right = FALSE))

##--- some values OUTSIDE the breaks :
table(cx  <- cut(x, br = 2*(0:4)))
table(cxl <- cut(x, br = 2*(0:4), right = FALSE))
which(is.na(cx));  x[is.na(cx)]  #-- the first 9  values  0
which(is.na(cxl)); x[is.na(cxl)] #-- the last  5  values  8

## Label construction:
y <- rnorm(100)
table(cut(y, breaks = pi/3*(-3:3)))
table(cut(y, breaks = pi/3*(-3:3), dig.lab=4))

table(cut(y, breaks =  1*(-3:3), dig.lab=4))
# extra digits don't "harm" here
table(cut(y, breaks =  1*(-3:3), right = FALSE))
#- the same, since no exact INT!

## sometimes the default dig.lab is not enough to be avoid confusion:
aaa <- c(1,2,3,4,5,2,3,4,5,6,7)
cut(aaa, 3)
cut(aaa, 3, dig.lab=4)

[Package base version 2.1.0 Index]