list version of var length int embedding

nb-virtdata/virtdata-lib-hdf5/src/main/java/io/nosqlbench/virtdata/library/hdf5/from_long/to_list/HdfFileToVarLengthIntList.java

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+/*
+ * Copyright (c) nosqlbench
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.nosqlbench.virtdata.library.hdf5.from_long.to_list;
+
+import io.nosqlbench.virtdata.api.annotations.Categories;
+import io.nosqlbench.virtdata.api.annotations.Category;
+import io.nosqlbench.virtdata.api.annotations.ThreadSafeMapper;
+import io.nosqlbench.virtdata.library.hdf5.from_long.AbstractHdfFileToVectorType;
+
+import java.util.List;
+import java.util.function.LongFunction;
+
+/**
+ * This function reads a vector dataset from an HDF5 file. The dataset itself is not
+ * read into memory, only the metadata (the "dataset" Java Object). The lambda function
+ * reads a single vector from the dataset, based on the long input value. As currently
+ * written this class will only work for datasets with 2 dimensions where the 1st dimension
+ * specifies the number of vectors and the 2nd dimension specifies the number of elements in
+ * each vector. Only datatypes short, int, and float are supported at this time.
+ * <p>
+ * This implementation is specific to returning a List of type Integer from a dataset that contains
+ * variable length arrays of ints.
+ */
+@ThreadSafeMapper
+@Categories(Category.experimental)
+public class HdfFileToVarLengthIntList extends AbstractHdfFileToVectorType implements LongFunction<List<Integer>> {
+
+    public HdfFileToVarLengthIntList(String filename, String datasetName) {
+        super(filename, datasetName);
+    }
+    @Override
+    public List<Integer> apply(long l) {
+        Object data = getDataFrom(l);
+        return extractIds(data, l);
+    }
+
+    /**
+     * @param o The dataset from hdf5 file. In this case because the number of ints in each array is variable length it
+     *          is returned by hdf5 as a one dimensional array of Objects
+     * @param l The current cycle
+     * @return A List of the integers at the offset of l
+     */
+    private List<Integer> extractIds(Object o, long l) {
+        Object[] objects = (Object[]) o;
+        int[] ints = (int[]) objects[(int) l % objects.length];
+        Integer[] integers = new Integer[ints.length];
+        for (int i = 0; i < ints.length; i++) {
+            integers[i] = ints[i];
+        }
+        return List.of(integers);
+    }
+
+}