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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
```
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