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# Red Gandiva - Gandiva Ruby

Red Gandiva is the Ruby bindings of Gandiva. Red Gandiva is based on GObject Introspection.

Gandiva is a toolset for compiling and evaluating expressions on Arrow data.

[GObject Introspection](https://wiki.gnome.org/action/show/Projects/GObjectIntrospection) is a middleware for language bindings of C library. GObject Introspection can generate language bindings automatically at runtime.

Red Gandiva uses [Gandiva GLib](https://github.com/apache/arrow/tree/master/c_glib/gandiva-glib) and [gobject-introspection gem](https://rubygems.org/gems/gobject-introspection) to generate Ruby bindings of Gandiva.

Gandiva GLib is a C wrapper for [Gandiva C++](https://github.com/apache/arrow/tree/master/cpp/gandiva). GObject Introspection can't use Gandiva C++ directly. Gandiva GLib is a bridge between Gandiva C++ and GObject Introspection.

gobject-introspection gem is a Ruby bindings of GObject Introspection. Red Gandiva uses GObject Introspection via gobject-introspection gem.

## Install

Install Gandiva GLib before install Red Gandiva. See [Apache Arrow install document](https://arrow.apache.org/install/) for details.

Install Red Gandiva after you install Gandiva GLib:

```text
% gem install red-gandiva
```

## Usage

```ruby
require "gandiva"

table = Arrow::Table.new(:field1 => Arrow::Int32Array.new([1, 2, 3, 4]),
                         :field2 => Arrow::Int32Array.new([11, 13, 15, 17]))
schema = table.schema

expression1 = schema.build_expression do |record|
  record.field1 + record.field2
end

expression2 = schema.build_expression do |record, context|
  context.if(record.field1 > record.field2)
    .then(record.field1 / record.field2)
    .else(record.field1)
end

projector = Gandiva::Projector.new(schema, [expression1, expression2])
table.each_record_batch do |record_batch|
  outputs = projector.evaluate(record_batch)
  puts outputs.collect(&:values))
end
```
