[Solved] Ruby # Discussion 1

We will be implementing a simple database using Ruby data structures to store the data. A database can contain an arbitrary number of tables. Each table will contain tuples of size *n*, where *n* is the number of columns in the table. Through a series of discussion exercises each week, we will improve upon our simple database. This week we will create a database representation that will implement some basic functionality. The class `Tuple` represents and entry in a table. The class `Table` represents a collection of tuples.

### Testing & Submitting

You will submit this project to [Gradescope](https://www.gradescope.com/courses/171498/assignments/644881). You may only submit the **disc1.rb** file. To test locally, run `ruby test/public/public.rb`.

## Part 1: `Tuple`

A `Tuple` represents a single entry, in a table. The methods below will be implemented in the `Tuple` class in [disc1.rb](src/disc1.rb).

#### `initialize(data)`

**Type**: `(Array) -> _` **Description**: Given an array of values for the tuple, store them in the `Tuple` object in any way you would like. You should perform any initialization steps for the `Tuple` instance here. The return value of this function does not matter. **Examples**:`rubyt = Tuple.new([a, 1, b, 2])t = Tuple.new([]) # Tuples may be empty`

#### `getSize()`

**Type**: `() -> Integer` **Description**: Return the number of entries in the `Tuple`. **Examples**:`rubyt = Tuple.new([a, 1, b, 2])t.getSize() # Returns 4u = Tuple.new([])u.getSize() # Returns 0`

#### `getData(index)`

**Type**: `(Integer) -> Object` **Description**: Return the data at a particular index of a `Tuple` (indexed starting at 0). If the provided index exceeds the largest index in the tuple, return `nil`. **Assumptions**: `index` is non-negative. **Examples**:`rubyt = Tuple.new([a, 1, b, 2])t.getData(0) # Returns at.getData(4) # Returns nil`

#### `self.getNumTuples(n)`

**Type**: `(Integer) -> Integer` **Description**: Return the number of `Tuple`s of size `n` that have ever been created. Hint: you should use a static variable to keep track of this. **Examples**:`rubyTuple.getNumTuples(3) # Returns 0t = Tuple.new([a, 1, b])t = Tuple.new([a, 1, b])Tuple.getNumTuples(3) # Returns 2t = Tuple.new([3])Tuple.getNumTuples(3) # Returns 2`

## Part 2: `Table`

A `Table` represents a collection of tuples. The methods below will be implemented in the `Table` class in [disc1.rb](src/disc1.rb).

#### `initialize(column_names)`

**Type**: `(Array) -> _` **Description**: Given an array of column names for the `Table`, store them in the object in any way you would like. You should perform any initialization steps for the `Table` instance here. The return value of this function does not matter. **Examples**:`rubyt = Table.new([c0, c1, c2])t = Table.new([])`

#### `insertTuple(tuple)`

**Type**: `(Tuple) -> boolean` **Description**: Insert a `Tuple` into the `Table`. Note that the number of entries in the `Tuple` must match the number of columns in the `Table`. If this is not the case, make no changes to the `Table` and return `false`. If the sizes match, insert the `Tuple` and return `true`. **Examples**:`rubytable = Table.new([a, b])x = Tuple.new([0, 1])y = Tuple.new([3, y])z = Tuple.new([1, 2, 3])

table.insertTuple(x) # Returns truetable.insertTuple(y) # Returns truetable.insertTuple(z) # Returns false (sizes do not match)`

#### `getSize()`

**Type**: `() -> Integer` **Description**: Return the number of `Tuple`s in the table. **Examples**:`rubytable = Table.new([a, b])table.getSize() # Returns 0x = Tuple.new([0, 1])table.getSize() # Returns 1`

#### `selectTuples(column_names)`

**Type**: `(Array) -> Table` **Description**: Return a new `Table` instance which is the same as the existing one, but only with the requested columns. Hint: to find the index of an element in an array, use `arr.index(element)`. This function should NOT modify the current table; rather, create a new one. **Assumptions**: `column_names` does not include any column names which are not present in the table (i.e. all queries are valid). **Examples**:`rubytable = Table.new([a, b, c])x = Tuple.new([0, 1, 2])y = Tuple.new([x, y, z])table.insertTuple(x)table.insertTuple(y)# The table currently looks like this:# a | b | c# ++# 0 | 1 | 2# x | y | z

table2 = table.selectTuples([a, c])# The call above should return a NEW table that looks like this:# a | c# +# 0 | 2# x | z`

#### `getTuples()`

**Type**: `() -> Array` **Description**: Return an array of the `Tuple`s present in the `Table`. **Examples**:`rubytable = Table.new([a, b, c])table.getTuples() # Returns []x = Tuple.new([0, 1, 2])y = Tuple.new([x, y, z])table.getTuples() # Returns [[0, 1, 2], [x, y, z]]`