Add nvtext::byte_pair_encoding API

cpp/CMakeLists.txt

@@ -470,8 +470,10 @@ add_library(
   src/text/normalize.cu
   src/text/replace.cu
   src/text/stemmer.cu
+  src/text/subword/bpe_tokenizer.cu
   src/text/subword/data_normalizer.cu
   src/text/subword/load_hash_file.cu
+  src/text/subword/load_merges_file.cu
   src/text/subword/subword_tokenize.cu
   src/text/subword/wordpiece_tokenizer.cu
   src/text/tokenize.cu

cpp/include/cudf/strings/detail/combine.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020-2021, NVIDIA CORPORATION.
+ * Copyright (c) 2020-2022, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -54,6 +54,20 @@ std::unique_ptr<column> join_strings(
   rmm::cuda_stream_view stream        = rmm::cuda_stream_default,
   rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource());
 
+/**
+ * @copydoc join_list_elements(table_view const&,string_scalar const&,string_scalar
+ * const&,separator_on_nulls,output_if_empty_list,rmm::mr::device_memory_resource*)
+ *
+ * @param stream CUDA stream used for device memory operations and kernel launches.
+ */
+std::unique_ptr<column> join_list_elements(lists_column_view const& lists_strings_column,
+                                           string_scalar const& separator,
+                                           string_scalar const& narep,
+                                           separator_on_nulls separate_nulls,
+                                           output_if_empty_list empty_list_policy,
+                                           rmm::cuda_stream_view stream,
+                                           rmm::mr::device_memory_resource* mr);
+
 }  // namespace detail
 }  // namespace strings
 }  // namespace cudf

cpp/include/nvtext/bpe_tokenize.hpp

@@ -0,0 +1,113 @@
+/*
+ * Copyright (c) 2022, NVIDIA CORPORATION.
+ *
+ * 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.
+ */
+#pragma once
+
+#include <cudf/column/column.hpp>
+#include <cudf/column/column_view.hpp>
+#include <cudf/scalar/scalar.hpp>
+#include <cudf/strings/strings_column_view.hpp>
+
+namespace nvtext {
+
+/**
+ * @addtogroup nvtext_tokenize
+ * @{
+ * @file
+ */
+
+/**
+ * @brief The table of merge pairs for the BPE encoder.
+ *
+ * To create an instance, call nvtext::load_merges_table
+ */
+struct bpe_merge_pairs {
+  struct bpe_merge_pairs_impl;
+  std::unique_ptr<bpe_merge_pairs_impl> impl{};
+
+  bpe_merge_pairs(std::unique_ptr<cudf::column>&& input,
+                  rmm::cuda_stream_view stream        = rmm::cuda_stream_default,
+                  rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource());
+
+  bpe_merge_pairs(cudf::strings_column_view const& input,
+                  rmm::cuda_stream_view stream        = rmm::cuda_stream_default,
+                  rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource());
+
+  ~bpe_merge_pairs();
+
+  cudf::size_type get_size();
+  std::size_t get_map_size();
+};
+
+/**
+ * @brief Create a nvtext::bpe_merge_pairs from an input file.
+ *
+ * The file should contain a pair of strings per line separated by
+ * a single space.
+ *
+ * Example:
+ * @code{.txt}
+ * e n
+ * i t
+ * i s
+ * ...
+ * @endcode
+ *
+ * The pairs are expected to be ordered in the file by their rank
+ * relative to each other. A pair earlier in the file has priority over
+ * any pairs below it.
+ *
+ * @param filename_merges Local file path of pairs encoded in UTF-8.
+ * @param mr Memory resource to allocate any returned objects.
+ */
+std::unique_ptr<bpe_merge_pairs> load_merge_pairs_file(
+  std::string const& filename_merges,
+  rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource());
+
+/**
+ * @brief Byte pair encode the input strings.
+ *
+ * This will split each string on whitespace, perform the encoding,
+ * and then build the output column using the given `separator`.
+ *
+ * The encoding algorithm rebuilds each string by matching substrings
+ * in the `merge_pairs` table and iteratively removing the minimum ranked pair
+ * until no pairs are left. Then, a space is inserted between the remaining
+ * pairs before the result is joined to make the output string.
+ *
+ * @code{.pseudo}
+ * mps = load_merges_file("merges.txt")
+ * input = ["test sentence", "thisis test"]
+ * result = byte_pair_encoding(input, mps)
+ * result is now ["test sent ence", "this is test"]
+ * @endcode
+ *
+ * @throw cudf::logic_error if `merge_pairs` is empty
+ * @throw cudf::logic_error if `separator` is invalid
+ *
+ * @param input Strings to encode.
+ * @param merge_pairs Created by a call to nvtext::load_merges_file.
+ * @param separator String used to build the output after encoding.
+ *                  Default is a space.
+ * @param mr Memory resource to allocate any returned objects.
+ */
+std::unique_ptr<cudf::column> byte_pair_encoding(
+  cudf::strings_column_view const& input,
+  bpe_merge_pairs const& merges_pairs,
+  cudf::string_scalar const& separator = cudf::string_scalar(" "),
+  rmm::mr::device_memory_resource* mr  = rmm::mr::get_current_device_resource());
+
+/** @} */  // end of group
+}  // namespace nvtext