\Header{cut}{Convert Numeric to Factor}
\methalias{cut.default}{cut}
\keyword{category}{cut}
\begin{Description}\relax
\code{cut} divides the range of \code{x} into intervals
and codes the values in \code{x} according to which
interval they fall.
The leftmost interval corresponds to level one,
the next leftmost to level two and so on.\end{Description}
\begin{Usage}
\begin{verbatim}
cut(x, ...)
cut.default(x, breaks, labels = NULL,
            include.lowest = FALSE, right = TRUE, dig.lab = 3, ...)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] a numeric vector which is to be converted to a factor by cutting.
\item[\code{breaks}] either a vector of cut points or number
giving the number of intervals which \code{x} is to be cut into.
\item[\code{labels}] labels for the levels of the resulting category.  By default,
labels are constructed using \code{"(a,b]"} interval notation. If
\code{labels = FALSE}, simple integer codes are returned instead of
a factor.
\item[\code{include.lowest}] logical, indicating if an `x[i]' equal to the
lowest (or highest, for \code{right = FALSE}) `breaks' value should be
included.
\item[\code{right}] logical, indicating if the intervals should closed on the
right (and open on the left) or vice versa.
\item[\code{dig.lab}] integer which is used when labels are not given. It
determines the number of digits used in formatting the break numbers.
\item[\code{...}] further arguments passed to or from other methods.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
If a \code{labels} parameter is specified, its values are used
to name the factor levels. If none is specified, the factor
level labels are constructed as \code{"(b1, b2]"}, \code{"(b2, b3]"}
etc. for \code{right=TRUE} and as \code{"[b1, b2)"}, \ldots if
\code{right=FALSE}.
In this case, \code{dig.lab} indicates how many digits should be used in
formatting the numbers \code{b1}, \code{b2}, \ldots.\end{Details}
\begin{Value}
A \code{\Link{factor}} is returned, unless \code{labels = FALSE} which
results in the mere integer level codes.\end{Value}
\begin{Note}\relax
Instead of \code{table(cut(x, br))}, \code{hist(x, br, plot = FALSE)} is
more efficient and less memory hungry.\end{Note}
\begin{SeeAlso}\relax
\code{\Link{split}} for splitting a variable according to a group factor;
\code{\Link{factor}}, \code{\Link{tabulate}}, \code{\Link{table}}.\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
Z <- rnorm(10000)
table(cut(Z, br = -6:6))
system.time(print(sum(table(cut(Z, br = -6:6, labels=FALSE)))))
system.time(print(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!
\end{ExampleCode}
\end{Examples}

