First commit

.gitignore

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+/.bundle/
+/.yardoc
+/_yardoc/
+/coverage/
+/doc/
+/pkg/
+/spec/reports/
+/tmp/

CHANGELOG.md

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+## 0.1.0
+
+- First release

Gemfile

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+source "https://rubygems.org"
+
+gemspec

Gemfile.lock

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+PATH
+  remote: .
+  specs:
+    lightgbm (0.1.0)
+      ffi
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    ffi (1.11.1)
+    minitest (5.11.3)
+    rake (12.3.3)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  bundler
+  lightgbm!
+  minitest (>= 5)
+  rake
+
+BUNDLED WITH
+   2.0.2

README.md

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+# LightGBM
+
+LightGBM for Ruby
+
+## Installation
+
+First, [install LightGBM](https://lightgbm.readthedocs.io/en/latest/Installation-Guide.html).
+
+Add this line to your application’s Gemfile:
+
+```ruby
+gem 'lightgbm'
+```
+
+Load a model
+
+```ruby
+booster = LightGBM::Booster.new(model_file: "model.txt")
+```
+
+Predict
+
+```ruby
+booster.predict([[1, 2], [3, 4]])
+```
+
+## Credits
+
+Thanks to the [xgboost](https://github.com/PairOnAir/xgboost-ruby) gem for serving as an initial reference.
+
+## History
+
+View the [changelog](https://github.com/ankane/lightgbm/blob/master/CHANGELOG.md)
+
+## Contributing
+
+Everyone is encouraged to help improve this project. Here are a few ways you can help:
+
+- [Report bugs](https://github.com/ankane/lightgbm/issues)
+- Fix bugs and [submit pull requests](https://github.com/ankane/lightgbm/pulls)
+- Write, clarify, or fix documentation
+- Suggest or add new features

Rakefile

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+require "bundler/gem_tasks"
+require "rake/testtask"
+
+task default: :test
+Rake::TestTask.new do |t|
+  t.libs << "test"
+  t.pattern = "test/**/*_test.rb"
+end

lib/lightgbm.rb

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+# dependencies
+require "ffi"
+
+# modules
+require "lightgbm/booster"
+require "lightgbm/ffi"
+require "lightgbm/version"

lib/lightgbm/booster.rb

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+module LightGBM
+  class Booster
+    def initialize(model_file:)
+      @handle = ::FFI::MemoryPointer.new(:pointer)
+      if model_file
+        out_num_iterations = ::FFI::MemoryPointer.new(:int)
+        check_result FFI.LGBM_BoosterCreateFromModelfile(model_file, out_num_iterations, @handle)
+      end
+      ObjectSpace.define_finalizer(self, self.class.finalize(handle_pointer))
+    end
+
+    def self.finalize(pointer)
+      -> { FFI.LGBM_BoosterFree(pointer) }
+    end
+
+    def predict(input)
+      raise TypeError unless input.is_a?(Array)
+
+      singular = input.first.is_a?(Array)
+      input = [input] unless singular
+
+      data = ::FFI::MemoryPointer.new(:float, input.count * input.first.count)
+      data.put_array_of_float(0, input.flatten)
+
+      out_len = ::FFI::MemoryPointer.new(:int64)
+      out_result = ::FFI::MemoryPointer.new(:double, input.count)
+      parameter = ""
+      check_result FFI.LGBM_BoosterPredictForMat(handle_pointer, data, 0, input.count, input.first.count, 1, 0, 0, parameter, out_len, out_result)
+      out = out_result.read_array_of_double(out_len.read_int64)
+
+      singular ? out : out.first
+    end
+
+    private
+
+    def check_result(err)
+      if err != 0
+        raise FFI.LGBM_GetLastError
+      end
+    end
+
+    def handle_pointer
+      @handle.read_pointer
+    end
+  end
+end

lib/lightgbm/ffi.rb

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+module LightGBM
+  module FFI
+    extend ::FFI::Library
+    ffi_lib ["lightgbm", "lib_lightgbm.so"]
+
+    # https://github.com/microsoft/LightGBM/blob/master/include/LightGBM/c_api.h
+    attach_function :LGBM_GetLastError, %i[], :string
+    attach_function :LGBM_BoosterCreate, %i[pointer string pointer], :int
+    attach_function :LGBM_BoosterCreateFromModelfile, %i[string pointer pointer], :int
+    attach_function :LGBM_BoosterFree, %i[pointer], :int
+    attach_function :LGBM_BoosterPredictForMat, %i[pointer pointer int int32 int32 int int int string pointer pointer], :int
+  end
+end

lib/lightgbm/version.rb

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+module LightGBM
+  VERSION = "0.1.0"
+end

lightgbm.gemspec

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+require_relative "lib/lightgbm/version"
+
+Gem::Specification.new do |spec|
+  spec.name          = "lightgbm"
+  spec.version       = LightGBM::VERSION
+  spec.summary       = "LightGBM for Ruby"
+  spec.homepage      = "https://github.com/ankane/lightgbm"
+  spec.license       = "MIT"
+
+  spec.author        = "Andrew Kane"
+  spec.email         = "andrew@chartkick.com"
+
+  spec.files         = Dir["*.{md,txt}", "{lib}/**/*"]
+  spec.require_path  = "lib"
+
+  spec.required_ruby_version = ">= 2.4"
+
+  spec.add_dependency "ffi"
+
+  spec.add_development_dependency "bundler"
+  spec.add_development_dependency "rake"
+  spec.add_development_dependency "minitest", ">= 5"
+end

test/lightgbm_test.rb

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+require_relative "test_helper"
+
+class LightGBMTest < Minitest::Test
+  def test_load_model
+    model = LightGBM::Booster.new(model_file: "test/support/model.txt")
+
+    x_test = [
+      [0.04417, 70.0, 2.24, 0, 0.400, 6.871, 47.4, 7.8278, 5, 358, 14.8, 390.86, 6.07],
+      [0.03537, 34.0, 6.09, 0, 0.433, 6.590, 40.4, 5.4917, 7, 329, 16.1, 395.75, 9.50]
+    ]
+    preds = model.predict(x_test)
+    assert_in_delta 28.29122797, preds[0]
+    assert_in_delta 25.87936514, preds[1]
+  end
+end