1\name{period.min}
2\alias{period.min}
3\title{ Calculate Min By Period }
4\description{
5Calculate a minimum for each period of INDEX. Essentially a rolling
6application of minimum over a series of non-overlapping sections.
7}
8\usage{
9period.min(x, INDEX)
10}
11\arguments{
12  \item{x}{ a univariate data object }
13  \item{INDEX}{ a numeric vector of endpoints to calculate maximum on }
14}
15\details{
16Used to calculate a minimum per period given an arbitrary
17index of sections to be calculated over. This is an optimized function
18for minimum. There are additional optimized versions for max, sum, and
19prod.
20
21For xts-coercible objects, an appropriate INDEX
22can be derived from a call to \code{endpoints}.
23}
24\value{
25An xts or zoo object of minimums, indexed by the period endpoints.
26}
27\author{ Jeffrey A. Ryan }
28\seealso{ \code{\link{endpoints}}, \code{\link{period.sum}},
29          \code{\link{period.max}}, \code{\link{period.prod}} }
30\examples{
31period.min(c(1,1,4,2,2,6,7,8,-1,20),c(0,3,5,8,10))
32
33data(sample_matrix)
34period.min(sample_matrix[,1],endpoints(sample_matrix))
35period.min(as.xts(sample_matrix)[,1],endpoints(sample_matrix))
36}
37\keyword{ utilities }% __ONLY ONE__ keyword per line
38