From 25abd43a25b7adccce9e556de6bb4e9528b24706 Mon Sep 17 00:00:00 2001
From: Will Bainbridge <http://cfd.direct>
Date: Wed, 16 Jun 2021 15:15:48 +0100
Subject: [PATCH] ListOps: Added count function to return the number of
 occurrences of a value in a list

---
 .../containers/Lists/ListOps/ListOps.H        |  4 ++++
 .../Lists/ListOps/ListOpsTemplates.C          | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/src/OpenFOAM/containers/Lists/ListOps/ListOps.H b/src/OpenFOAM/containers/Lists/ListOps/ListOps.H
index 82abf8e064..5b4299a6e9 100644
--- a/src/OpenFOAM/containers/Lists/ListOps/ListOps.H
+++ b/src/OpenFOAM/containers/Lists/ListOps/ListOps.H
@@ -168,6 +168,10 @@ List<OutList> invertManyToMany(const label len, const UList<InList>& in)
 //- Create identity map (map[i] == i) of given length
 labelList identity(const label len);
 
+//- Count the number of occurrences of a value in a list
+template<class ListType>
+label count(const ListType& l, typename ListType::const_reference x);
+
 //- Find first occurrence of given element and return index,
 //  return -1 if not found. Linear search.
 template<class ListType>
diff --git a/src/OpenFOAM/containers/Lists/ListOps/ListOpsTemplates.C b/src/OpenFOAM/containers/Lists/ListOps/ListOpsTemplates.C
index bf3a719dd6..6737d1be53 100644
--- a/src/OpenFOAM/containers/Lists/ListOps/ListOpsTemplates.C
+++ b/src/OpenFOAM/containers/Lists/ListOps/ListOpsTemplates.C
@@ -475,6 +475,25 @@ void Foam::invertManyToMany
 }
 
 
+template<class ListType>
+Foam::label Foam::count
+(
+    const ListType& l,
+    typename ListType::const_reference x
+)
+{
+    label result = 0;
+    forAll(l, i)
+    {
+        if (l[i] == x)
+        {
+            ++ result;
+        }
+    }
+    return result;
+}
+
+
 template<class ListType>
 Foam::label Foam::findIndex
 (