7 files changed, 105 insertions(+), 5 deletions(-)

M ChangeLog
M DESCRIPTION
M NAMESPACE
M NEWS
A R/next_subset.R
M man/neighbourfun.Rd
A man/next_subset.Rd

@@ 1,7 1,11 @@
+2023-06-29  Enrico Schumann  <es@enricoschumann.net>
+
+        * R/next_subset.R (next_subset): add function
+
 2022-08-22  Enrico Schumann  <es@enricoschumann.net>
 
-	* DESCRIPTION (Version): 0.1-2
-	(Suggests): add 'quadprog', used in vignette
+        * DESCRIPTION (Version): 0.1-2
+        (Suggests): add 'quadprog', used in vignette
 
 2022-08-19  Enrico Schumann  <es@enricoschumann.net>
 

@@ 1,8 1,8 @@
 Package: neighbours
 Type: Package
 Title: Neighbourhood Functions for Local-Search Algorithms
-Version: 0.1-2
-Date: 2022-08-22
+Version: 0.1-3
+Date: 2023-06-29
 Maintainer: Enrico Schumann <es@enricoschumann.net>
 Authors@R: person(given = "Enrico", family = "Schumann",
                   role  = c("aut", "cre"),

@@ 2,4 2,5 @@ importFrom("stats", "runif")
 
 export("neighbourfun",
        "neighborfun",
+       "next_subset",
        "compare_vectors")

@@ 1,3 1,16 @@
+v0.1-3  (2023-07-??; not yet released)
+
+  o New function "next_subset" for computing the next
+    k-of-n subset.
+
+v0.1-2  (2022-08-22)
+
+  o No user visible changes.
+
+v0.1-1  (2022-08-17)
+
+  o No user visible changes.
+
 v0.1-0  (2022-08-16)
 
   o Initial release.  The package provides a function

@@ 0,0 1,10 @@
+next_subset <- function(a, n, k) {
+    if (a[1L] == n - k +1)
+        return(NULL)
+    k1 <- 1:k
+    h <- min(which(a[k + 1 - k1] != n + 1 - k1))
+    m1 <- a[k + 1 - h]
+    h1 <- 1:h
+    a[k + h1 - h] <- m1 + h1
+    a
+}

@@ 113,7 113,8 @@ neighborfun (min = 0, max = 1, kmin = NULL, kmax = NULL,
   Methods and Optimization in Finance}. 2nd edition. Elsevier.\cr
   \url{https://www.elsevier.com/books/numerical-methods-and-optimization-in-finance/gilli/978-0-12-815065-8}
 
-  Schumann, E. (2019) Financial Optimisation with R (\pkg{NMOF} Manual).\cr
+  Schumann, E. (2023) \emph{Financial Optimisation with R
+    (\pkg{NMOF} Manual)}.\cr
   \url{http://enricoschumann.net/NMOF.htm#NMOFmanual}
 
 }

@@ 0,0 1,71 @@
+\name{next_subset}
+\alias{next_subset}
+\title{
+  Select Next Subset
+}
+\description{
+Select next subset of size k from a set of size n.
+}
+\usage{
+next_subset(a, n, k)
+}
+\arguments{
+  \item{a}{
+    a numeric vector (integers)
+}
+  \item{n}{
+    an integer: the size of the set to choose from
+}
+  \item{k}{
+    an integer: the subset size
+}
+}
+\details{
+
+  Given a subset \emph{a} of size \emph{k} taken from a set
+  of size \emph{n}, compute the next subset by alphabetical
+  order.
+
+  Uses algorithm NEXKSB of Nijenhuis and Wilf (1975).
+}
+\value{
+   a numeric vector (the next subset) or \code{\link{NULL}}
+   (when there is no next subset)
+}
+\references{
+  Nijenhuis, A. and Wilf, H. S. (1975)
+  \emph{Combinatorial Algorithms for Computers and Calculators}.
+  Academic Press.
+}
+\author{
+  Enrico Schumann
+}
+\seealso{
+
+  \code{\link{choose}} computes the number of combinations\cr
+  \code{\link{combn}} creates all combinations\cr
+  \code{\link{expand.grid}}
+}
+\examples{
+n <- 4
+k <- 2
+t(combn(n, k))
+##      [,1] [,2]
+## [1,]    1    2
+## [2,]    1    3
+## [3,]    1    4
+## [4,]    2    3
+## [5,]    2    4
+## [6,]    3    4
+
+a <- 1:k
+print(a)
+while (!is.null(a))
+    print(a <- next_subset(a, n = n, k = k))
+## [1] 1 2
+## [1] 1 3
+## [1] 1 4
+## [1] 2 3
+## [1] 2 4
+## [1] 3 4
+}