feat: Add cycles-related functions

Author: heavywatal

NAMESPACE

@@ -87,9 +87,12 @@ export(igraph_version)
 export(incident)
 export(induced_subgraph)
 export(induced_subgraph_edges)
+export(is_acyclic)
 export(is_biconnected)
 export(is_connected)
+export(is_dag)
 export(is_directed)
+export(is_eulerian)
 export(is_igraph)
 export(is_simple)
 export(is_sink)

R/cpp11.R

@@ -168,6 +168,14 @@ is_biconnected_ <- function(graph) {
   .Call(`_igraphlite_is_biconnected_`, graph)
 }
 
+is_dag_ <- function(graph) {
+  .Call(`_igraphlite_is_dag_`, graph)
+}
+
+is_eulerian_ <- function(graph) {
+  .Call(`_igraphlite_is_eulerian_`, graph)
+}
+
 as_adjlist_ <- function(graph, mode, loops, multiple) {
   .Call(`_igraphlite_as_adjlist_`, graph, mode, loops, multiple)
 }
@@ -440,6 +448,10 @@ is_simple_ <- function(graph, directed) {
   .Call(`_igraphlite_is_simple_`, graph, directed)
 }
 
+is_acyclic_ <- function(graph) {
+  .Call(`_igraphlite_is_acyclic_`, graph)
+}
+
 has_loop_ <- function(graph) {
   .Call(`_igraphlite_has_loop_`, graph)
 }

R/cycles.R

@@ -0,0 +1,49 @@
+#' Acyclic graphs and feedback sets
+#'
+#' A directed acyclic graph (DAG) is a directed graph with no directed cycles.
+#' For directed graphs, only directed cycles are considered.
+#' @inheritParams common_params
+#' @returns A logical value.
+#' @source <https://igraph.org/c/doc/igraph-Cycles.html#acyclic-graphs-feedback-sets>
+#' @rdname cycles-acyclic
+#' @export
+#' @examples
+#' dag = graph_tree(5L)
+#' tree = graph_tree(5L, mode = 2L)
+#' ring = graph_ring(5L)
+#'
+#' is_dag(dag)
+#' is_dag(tree)
+#' is_dag(ring)
+#'
+#' is_acyclic(dag)
+#' is_acyclic(tree)
+#' is_acyclic(ring)
+is_dag = function(graph) {
+  .Call(`_igraphlite_is_dag_`, graph)
+}
+
+#' @rdname cycles-acyclic
+#' @export
+is_acyclic = function(graph) {
+  .Call(`_igraphlite_is_acyclic_`, graph)
+}
+
+#' Eulerian cycles and paths
+#'
+#' An Eulerian path traverses each edge of the graph precisely once.
+#' A closed Eulerian path is referred to as an Eulerian cycle.
+#' @inheritParams common_params
+#' @returns A logical value with two elements: "has a path" and "has a cycle".
+#' @source <https://igraph.org/c/doc/igraph-Cycles.html#eulerian-cycles>
+#' @rdname cycles-eulerian
+#' @export
+#' @examples
+#' is_eulerian(graph_tree(5L))
+#'
+#' is_eulerian(graph_square_lattice(5L))
+#'
+#' is_eulerian(graph_ring(5L))
+is_eulerian = function(graph) {
+  .Call(`_igraphlite_is_eulerian_`, graph)
+}

_pkgdown.yml

@@ -56,6 +56,11 @@ reference:
   - components
   - centrality
   - is_simple
+- title: Graph cycles
+  desc: https://igraph.org/c/doc/igraph-Cycles.html
+- contents:
+  - is_acyclic
+  - is_eulerian
 - title: Generating Layouts for Graph Drawing
   desc: https://igraph.org/c/doc/igraph-Layout.html
 - contents:

man/cycles-acyclic.Rd

@@ -307,6 +307,20 @@ extern "C" SEXP _igraphlite_is_biconnected_(SEXP graph) {
     return cpp11::as_sexp(is_biconnected_(cpp11::as_cpp<cpp11::decay_t<const cpp11::external_pointer<IGraph>>>(graph)));
   END_CPP11
 }
+// cycles.cpp
+bool is_dag_(const cpp11::external_pointer<IGraph> graph);
+extern "C" SEXP _igraphlite_is_dag_(SEXP graph) {
+  BEGIN_CPP11
+    return cpp11::as_sexp(is_dag_(cpp11::as_cpp<cpp11::decay_t<const cpp11::external_pointer<IGraph>>>(graph)));
+  END_CPP11
+}
+// cycles.cpp
+SEXP is_eulerian_(const cpp11::external_pointer<IGraph> graph);
+extern "C" SEXP _igraphlite_is_eulerian_(SEXP graph) {
+  BEGIN_CPP11
+    return cpp11::as_sexp(is_eulerian_(cpp11::as_cpp<cpp11::decay_t<const cpp11::external_pointer<IGraph>>>(graph)));
+  END_CPP11
+}
 // data.cpp
 SEXP as_adjlist_(const cpp11::external_pointer<IGraph> graph, const int mode, const int loops, const bool multiple);
 extern "C" SEXP _igraphlite_as_adjlist_(SEXP graph, SEXP mode, SEXP loops, SEXP multiple) {
@@ -796,6 +810,13 @@ extern "C" SEXP _igraphlite_is_simple_(SEXP graph, SEXP directed) {
   END_CPP11
 }
 // structural.cpp
+bool is_acyclic_(const cpp11::external_pointer<IGraph> graph);
+extern "C" SEXP _igraphlite_is_acyclic_(SEXP graph) {
+  BEGIN_CPP11
+    return cpp11::as_sexp(is_acyclic_(cpp11::as_cpp<cpp11::decay_t<const cpp11::external_pointer<IGraph>>>(graph)));
+  END_CPP11
+}
+// structural.cpp
 bool has_loop_(const cpp11::external_pointer<IGraph> graph);
 extern "C" SEXP _igraphlite_has_loop_(SEXP graph) {
   BEGIN_CPP11
@@ -941,9 +962,12 @@ static const R_CallMethodDef CallEntries[] = {
     {"_igraphlite_incident_",                         (DL_FUNC) &_igraphlite_incident_,                         4},
     {"_igraphlite_induced_subgraph_",                 (DL_FUNC) &_igraphlite_induced_subgraph_,                 3},
     {"_igraphlite_induced_subgraph_edges_",           (DL_FUNC) &_igraphlite_induced_subgraph_edges_,           2},
+    {"_igraphlite_is_acyclic_",                       (DL_FUNC) &_igraphlite_is_acyclic_,                       1},
     {"_igraphlite_is_biconnected_",                   (DL_FUNC) &_igraphlite_is_biconnected_,                   1},
     {"_igraphlite_is_connected_",                     (DL_FUNC) &_igraphlite_is_connected_,                     2},
+    {"_igraphlite_is_dag_",                           (DL_FUNC) &_igraphlite_is_dag_,                           1},
     {"_igraphlite_is_directed_",                      (DL_FUNC) &_igraphlite_is_directed_,                      1},
+    {"_igraphlite_is_eulerian_",                      (DL_FUNC) &_igraphlite_is_eulerian_,                      1},
     {"_igraphlite_is_simple_",                        (DL_FUNC) &_igraphlite_is_simple_,                        2},
     {"_igraphlite_k_regular_game_",                   (DL_FUNC) &_igraphlite_k_regular_game_,                   4},
     {"_igraphlite_layout_circle_",                    (DL_FUNC) &_igraphlite_layout_circle_,                    2},

man/cycles-eulerian.Rd

@@ -0,0 +1,22 @@
+// <https://igraph.org/c/doc/igraph-Cycles.html>
+#include "igraph.hpp"
+
+#include <igraph/igraph_cycles.h>
+#include <igraph/igraph_eulerian.h>
+
+#include <cpp11/logicals.hpp>
+
+[[cpp11::register]] bool
+is_dag_(const cpp11::external_pointer<IGraph> graph) {
+  igraph_bool_t res;
+  igraph_is_dag(graph->data(), &res);
+  return res;
+}
+
+[[cpp11::register]] SEXP
+is_eulerian_(const cpp11::external_pointer<IGraph> graph) {
+  igraph_bool_t has_path;
+  igraph_bool_t has_cycle;
+  igraph_is_eulerian(graph->data(), &has_path, &has_cycle);
+  return cpp11::writable::logicals{has_path, has_cycle};
+}

src/cpp11.cpp

@@ -20,6 +20,13 @@ is_simple_(const cpp11::external_pointer<IGraph> graph, const bool directed) {
   return res;
 }
 
+[[cpp11::register]] bool
+is_acyclic_(const cpp11::external_pointer<IGraph> graph) {
+  igraph_bool_t res;
+  igraph_is_acyclic(graph->data(), &res);
+  return res;
+}
+
 [[cpp11::register]] bool
 has_loop_(const cpp11::external_pointer<IGraph> graph) {
   igraph_bool_t res;

src/cycles.cpp

@@ -0,0 +1,19 @@
+test_that("acyclic tests work", {
+  dag = graph_tree(5L)
+  tree = graph_tree(5L, mode = 2L)
+  ring = graph_ring(5L)
+
+  expect_true(is_dag(dag))
+  expect_false(is_dag(tree))
+  expect_false(is_dag(ring))
+
+  expect_true(is_acyclic(dag))
+  expect_true(is_acyclic(tree))
+  expect_false(is_acyclic(ring))
+})
+
+test_that("eulerian test works", {
+  expect_identical(is_eulerian(graph_tree(5L)), c(FALSE, FALSE))
+  expect_identical(is_eulerian(graph_square_lattice(5L)), c(TRUE, FALSE))
+  expect_identical(is_eulerian(graph_ring(5L)), c(TRUE, TRUE))
+})