feat: max_degree() (#1403)

NAMESPACE

@@ -658,6 +658,7 @@ export(max_bipartite_match)
 export(max_cardinality)
 export(max_cliques)
 export(max_cohesion)
+export(max_degree)
 export(max_flow)
 export(maxcohesion)
 export(maximal.cliques)

R/aaa-auto.R

@@ -1309,6 +1309,21 @@ reciprocity_impl <- function(graph, ignore.loops=TRUE, mode=c("default", "ratio"
   res
 }
 
+maxdegree_impl <- function(graph, ..., v=V(graph), mode=c("all", "out", "in", "total"), loops=TRUE) {
+  # Argument checks
+  check_dots_empty()
+  ensure_igraph(graph)
+  v <- as_igraph_vs(graph, v)
+  mode <- switch(igraph.match.arg(mode), "out"=1L, "in"=2L, "all"=3L, "total"=3L)
+  loops <- as.logical(loops)
+
+  on.exit( .Call(R_igraph_finalizer) )
+  # Function call
+  res <- .Call(R_igraph_maxdegree, graph, v-1, mode, loops)
+
+  res
+}
+
 density_impl <- function(graph, loops=FALSE) {
   # Argument checks
   ensure_igraph(graph)

R/structural.properties.R

@@ -595,14 +595,17 @@ mean_distance <- average_path_length_dijkstra_impl
 #' @param normalized Logical scalar, whether to normalize the degree.  If
 #'   `TRUE` then the result is divided by \eqn{n-1}, where \eqn{n} is the
 #'   number of vertices in the graph.
-#' @param \dots Additional arguments to pass to `degree()`, e.g. `mode`
-#'   is useful but also `v` and `loops` make sense.
+#' @inheritParams rlang::args_dots_empty
 #' @return For `degree()` a numeric vector of the same length as argument
 #'   `v`.
 #'
 #'   For `degree_distribution()` a numeric vector of the same length as the
 #'   maximum degree plus one. The first element is the relative frequency zero
 #'   degree vertices, the second vertices with degree one, etc.
+#'
+#'   For `max_degree()`, the largest degree in the graph. When no vertices are
+#'   selected, or when the input is the null graph, zero is returned as this
+#'   is the smallest possible degree.
 #' @author Gabor Csardi \email{csardi.gabor@@gmail.com}
 #' @keywords graphs
 #' @family structural.properties
@@ -612,6 +615,7 @@ mean_distance <- average_path_length_dijkstra_impl
 #' g <- make_ring(10)
 #' degree(g)
 #' g2 <- sample_gnp(1000, 10 / 1000)
+#' max_degree(g2)
 #' degree_distribution(g2)
 #'
 degree <- function(graph, v = V(graph),
@@ -641,6 +645,10 @@ degree <- function(graph, v = V(graph),
   res
 }
 
+#' @rdname degree
+#' @export
+max_degree <- maxdegree_impl
+
 #' @rdname degree
 #' @param cumulative Logical; whether the cumulative degree distribution is to
 #'   be calculated.

src/cpp11.cpp

@@ -325,6 +325,7 @@ extern SEXP R_igraph_local_scan_k_ecount_them(SEXP, SEXP, SEXP, SEXP, SEXP);
 extern SEXP R_igraph_local_scan_neighborhood_ecount(SEXP, SEXP, SEXP);
 extern SEXP R_igraph_local_scan_subset_ecount(SEXP, SEXP, SEXP);
 extern SEXP R_igraph_make_weak_ref(SEXP, SEXP, SEXP);
+extern SEXP R_igraph_maxdegree(SEXP, SEXP, SEXP, SEXP);
 extern SEXP R_igraph_maxflow(SEXP, SEXP, SEXP, SEXP);
 extern SEXP R_igraph_maximal_cliques(SEXP, SEXP, SEXP, SEXP);
 extern SEXP R_igraph_maximal_cliques_count(SEXP, SEXP, SEXP, SEXP);
@@ -787,6 +788,7 @@ static const R_CallMethodDef CallEntries[] = {
     {"R_igraph_local_scan_neighborhood_ecount",             (DL_FUNC) &R_igraph_local_scan_neighborhood_ecount,              3},
     {"R_igraph_local_scan_subset_ecount",                   (DL_FUNC) &R_igraph_local_scan_subset_ecount,                    3},
     {"R_igraph_make_weak_ref",                              (DL_FUNC) &R_igraph_make_weak_ref,                               3},
+    {"R_igraph_maxdegree",                                  (DL_FUNC) &R_igraph_maxdegree,                                   4},
     {"R_igraph_maxflow",                                    (DL_FUNC) &R_igraph_maxflow,                                     4},
     {"R_igraph_maximal_cliques",                            (DL_FUNC) &R_igraph_maximal_cliques,                             4},
     {"R_igraph_maximal_cliques_count",                      (DL_FUNC) &R_igraph_maximal_cliques_count,                       4},

src/rinterface.c

@@ -3936,6 +3936,41 @@ SEXP R_igraph_reciprocity(SEXP graph, SEXP ignore_loops, SEXP mode) {
   return(r_result);
 }
 
+/*-------------------------------------------/
+/ igraph_maxdegree                           /
+/-------------------------------------------*/
+SEXP R_igraph_maxdegree(SEXP graph, SEXP vids, SEXP mode, SEXP loops) {
+                                        /* Declarations */
+  igraph_t c_graph;
+  igraph_integer_t c_res;
+  igraph_vs_t c_vids;
+  igraph_neimode_t c_mode;
+  igraph_bool_t c_loops;
+  SEXP res;
+
+  SEXP r_result;
+                                        /* Convert input */
+  R_SEXP_to_igraph(graph, &c_graph);
+  c_res=0;
+  igraph_vector_int_t c_vids_data;
+  R_SEXP_to_igraph_vs(vids, &c_graph, &c_vids, &c_vids_data);
+  c_mode = (igraph_neimode_t) Rf_asInteger(mode);
+  IGRAPH_R_CHECK_BOOL(loops);
+  c_loops = LOGICAL(loops)[0];
+                                        /* Call igraph */
+  IGRAPH_R_CHECK(igraph_maxdegree(&c_graph, &c_res, c_vids, c_mode, c_loops));
+
+                                        /* Convert output */
+  PROTECT(res=NEW_NUMERIC(1));
+  REAL(res)[0]=(double) c_res;
+  igraph_vector_int_destroy(&c_vids_data);
+  igraph_vs_destroy(&c_vids);
+  r_result = res;
+
+  UNPROTECT(1);
+  return(r_result);
+}
+
 /*-------------------------------------------/
 / igraph_density                             /
 /-------------------------------------------*/

tests/testthat/test-degree.R

@@ -26,3 +26,14 @@ test_that("degree works", {
     degree(g2, mode = "all", normalized = TRUE)
   )
 })
+
+test_that("max_degree works", {
+  g <- make_graph(c(1,2, 2,2, 2,3), directed = TRUE)
+  expect_equal(max_degree(g), 4)
+  expect_equal(max_degree(g, mode = "out"), 2)
+  expect_equal(max_degree(g, loops = FALSE), 2)
+  expect_equal(max_degree(g, mode = "out", loops = FALSE), 1)
+  expect_equal(max_degree(g, mode = "in", loops = FALSE), 1)
+  expect_equal(max_degree(g, v = c()), 0)
+  expect_equal(max_degree(make_empty_graph()), 0)
+})

tools/stimulus/functions-R.yaml

@@ -483,7 +483,9 @@ igraph_constraint:
     IGNORE: RR, RC
 
 igraph_maxdegree:
-    IGNORE: RR, RC, RInit
+    PARAM_ORDER: graph, *, vids, ...
+    PARAM_NAMES:
+        vids: v
 
 igraph_density: