MeshTools: added removeDuplicatesInPlaceInto().

I need to put the resulting index array into a pre-existing allocation.

src/Magnum/MeshTools/RemoveDuplicates.cpp

@@ -44,20 +44,21 @@ struct ArrayHash {
     }
 };
 
-std::pair<Containers::Array<UnsignedInt>, std::size_t> removeDuplicatesInPlace(const Containers::StridedArrayView2D<char>& data) {
+std::size_t removeDuplicatesInPlaceInto(const Containers::StridedArrayView2D<char>& data, const Containers::StridedArrayView1D<UnsignedInt>& indices) {
     /* Assuming the second dimension is contiguous so we can calculate the
        hashes easily */
     CORRADE_ASSERT(data.empty()[0] || data.isContiguous<1>(),
-        "MeshTools::removeDuplicatesInPlace(): second data view dimension is not contiguous", {});
+        "MeshTools::removeDuplicatesInPlaceInto(): second data view dimension is not contiguous", {});
 
     const std::size_t dataSize = data.size()[0];
+    CORRADE_ASSERT(indices.size() == dataSize,
+        "MeshTools::removeDuplicatesInPlaceInto(): output index array has" << indices.size() << "elements but expected" << dataSize, {});
+
     /* Table containing index of first occurence for each unique entry.
        Reserving more buckets than necessary (i.e. as if each entry was
        unique). */
     std::unordered_map<Containers::ArrayView<const char>, UnsignedInt, ArrayHash, ArrayEqual> table{dataSize};
 
-    Containers::Array<UnsignedInt> remapping{Containers::NoInit, dataSize};
-
     /* Go through all entries */
     for(std::size_t i = 0; i != dataSize; ++i) {
         /* Try to insert new entry into the table */
@@ -65,7 +66,7 @@ std::pair<Containers::Array<UnsignedInt>, std::size_t> removeDuplicatesInPlace(c
         const auto result = table.emplace(entry, table.size());
 
         /* Add the (either new or already existing) index into the array */
-        remapping[i] = result.first->second;
+        indices[i] = result.first->second;
 
         /* If this is a new combination, copy the data to new (earlier)
            position in the array. Data in [table.size()-1, i) are already
@@ -76,7 +77,13 @@ std::pair<Containers::Array<UnsignedInt>, std::size_t> removeDuplicatesInPlace(c
     }
 
     CORRADE_INTERNAL_ASSERT(dataSize >= table.size());
-    return {std::move(remapping), table.size()};
+    return table.size();
+}
+
+std::pair<Containers::Array<UnsignedInt>, std::size_t> removeDuplicatesInPlace(const Containers::StridedArrayView2D<char>& data) {
+    Containers::Array<UnsignedInt> indices{Containers::NoInit, data.size()[0]};
+    const std::size_t size = removeDuplicatesInPlaceInto(data, indices);
+    return {std::move(indices), size};
 }
 
 namespace {

src/Magnum/MeshTools/RemoveDuplicates.h

@@ -74,6 +74,19 @@ instead. Usage example:
 */
 MAGNUM_MESHTOOLS_EXPORT std::pair<Containers::Array<UnsignedInt>, std::size_t> removeDuplicatesInPlace(const Containers::StridedArrayView2D<char>& data);
 
+/**
+@brief Remove duplicate data from given array in-place
+@param[in,out] data     Data array, duplicate items will be cut away with order
+    preserved
+@param[out]    indices  Where to put the resulting index array
+@return Size of unique prefix in the cleaned up @p data array
+@m_since_latest
+
+Same as above, except that the index array is not allocated but put into
+@p indices instead. Expects that @p indices has the same size as @p data.
+*/
+MAGNUM_MESHTOOLS_EXPORT std::size_t removeDuplicatesInPlaceInto(const Containers::StridedArrayView2D<char>& data, const Containers::StridedArrayView1D<UnsignedInt>& indices);
+
 /**
 @brief Remove duplicates from indexed data in-place
 @param[in,out] indices  Index array, which will get remapped to list just

src/Magnum/MeshTools/Test/RemoveDuplicatesTest.cpp

@@ -38,6 +38,7 @@ struct RemoveDuplicatesTest: TestSuite::Tester {
 
     void removeDuplicatesInPlace();
     void removeDuplicatesInPlaceNonContiguous();
+    void removeDuplicatesInPlaceIntoWrongOutputSize();
     template<class T> void removeDuplicatesIndexedInPlace();
     void removeDuplicatesIndexedInPlaceSmallType();
     void removeDuplicatesIndexedInPlaceEmptyIndices();
@@ -56,6 +57,7 @@ struct RemoveDuplicatesTest: TestSuite::Tester {
 RemoveDuplicatesTest::RemoveDuplicatesTest() {
     addTests({&RemoveDuplicatesTest::removeDuplicatesInPlace,
               &RemoveDuplicatesTest::removeDuplicatesInPlaceNonContiguous,
+              &RemoveDuplicatesTest::removeDuplicatesInPlaceIntoWrongOutputSize,
               &RemoveDuplicatesTest::removeDuplicatesIndexedInPlace<UnsignedByte>,
               &RemoveDuplicatesTest::removeDuplicatesIndexedInPlace<UnsignedShort>,
               &RemoveDuplicatesTest::removeDuplicatesIndexedInPlace<UnsignedInt>,
@@ -92,7 +94,19 @@ void RemoveDuplicatesTest::removeDuplicatesInPlaceNonContiguous() {
     std::ostringstream out;
     Error redirectError{&out};
     MeshTools::removeDuplicatesInPlace(Containers::arrayCast<2, char>(Containers::arrayView(data)).every({1, 2}));
-    CORRADE_COMPARE(out.str(), "MeshTools::removeDuplicatesInPlace(): second data view dimension is not contiguous\n");
+    CORRADE_COMPARE(out.str(), "MeshTools::removeDuplicatesInPlaceInto(): second data view dimension is not contiguous\n");
+}
+
+void RemoveDuplicatesTest::removeDuplicatesInPlaceIntoWrongOutputSize() {
+    Int data[8]{};
+    UnsignedInt output[7];
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    MeshTools::removeDuplicatesInPlaceInto(
+        Containers::arrayCast<2, char>(Containers::arrayView(data)),
+        output);
+    CORRADE_COMPARE(out.str(), "MeshTools::removeDuplicatesInPlaceInto(): output index array has 7 elements but expected 8\n");
 }
 
 template<class T> void RemoveDuplicatesTest::removeDuplicatesIndexedInPlace() {