Julia - Tuples

Similar to an array, tuple is also an ordered set of elements. Tuples work in almost the same way as arrays but there are following important differences between them −

  • An array is represented by square brackets whereas a tuple is represented by parentheses and commas.

  • Tuples are immutable.

Creating tuples

We can create tuples as arrays and most of the array’s functions can be used on tuples also. Some of the example are given below −

julia> tupl=(5,10,15,20,25,30)
(5, 10, 15, 20, 25, 30)

julia> tupl
(5, 10, 15, 20, 25, 30)

julia> tupl[3:end]
(15, 20, 25, 30)

julia> tupl = ((1,2),(3,4))

((1, 2), (3, 4))

julia> tupl[1]
(1, 2)

julia> tupl[1][2]
2

We cannot change a tuple:
julia> tupl[2]=0
ERROR: MethodError: no method matching setindex!(::Tuple{Tuple{Int64,Int64},Tuple{Int64,Int64}}, ::Int64, ::Int64)
Stacktrace:
 [1] top-level scope at REPL[7]:1

Named tuples

A named tuple is simply a combination of a tuple and a dictionary because −

  • A named tuple is ordered and immutable like a tuple and

  • Like a dictionary in named tuple, each element has a unique key which can be used to access it.

In next section, let us see how we can create named tuples −

Creating named tuples

You can create named tuples in Julia by −

  • Providing keys and values in separate tuples

  • Providing keys and values in a single tuple

  • Combining two existing named tuples

Keys and values in separate tuples

One way to create named tuples is by providing keys and values in separate tuples.

Example

julia> names_shape = (:corner1, :corner2)
(:corner1, :corner2)

julia> values_shape = ((100, 100), (200, 200))
((100, 100), (200, 200))

julia> shape_item2 = NamedTuple{names_shape}(values_shape)
(corner1 = (100, 100), corner2 = (200, 200))

We can access the elements by using dot(.) syntax −

julia> shape_item2.corner1
(100, 100)

julia> shape_item2.corner2
(200, 200)

Keys and values in a single tuple

We can also create named tuples by providing keys and values in a single tuple.

Example

julia> shape_item = (corner1 = (1, 1), corner2 = (-1, -1), center = (0, 0))
(corner1 = (1, 1), corner2 = (-1, -1), center = (0, 0))

We can access the elements by using dot(.) syntax −

julia> shape_item.corner1
(1, 1)

julia> shape_item.corner2
(-1, -1)

julia> shape_item.center
(0, 0)

julia> (shape_item.center,shape_item.corner2)
((0, 0), (-1, -1))

We can also access all the values as with ordinary tuples as follows −

julia> c1, c2, center = shape_item
(corner1 = (1, 1), corner2 = (-1, -1), center = (0, 0))

julia> c1
(1, 1)

Combining two named tuples

Julia provides us a way to make new named tuples by combining two named tuples together as follows −

Example

julia> colors_shape = (top = "red", bottom = "green")
(top = "red", bottom = "green")

julia> shape_item = (corner1 = (1, 1), corner2 = (-1, -1), center = (0, 0))
(corner1 = (1, 1), corner2 = (-1, -1), center = (0, 0))

julia> merge(shape_item, colors_shape)
(corner1 = (1, 1), corner2 = (-1, -1), center = (0, 0), top = "red", bottom = "green")

Named tuples as keyword arguments

If you want to pass a group of keyword arguments to a function, named tuple is a convenient way to do so in Julia. Following is the example of a function that accepts three keyword arguments −

julia> function ABC(x, y, z; a=10, b=20, c=30)
         println("x = $x, y = $y, z = $z; a = $a, b = $b, c = $c")
      end
ABC (generic function with 1 method)

It is also possible to define a named tuple which contains the names as well values for one or more keywords as follows −

julia> options = (b = 200, c = 300)
(b = 200, c = 300)

In order to pass the named tuples to the function we need to use; while calling the function −

julia> ABC(1, 2, 3; options...)
x = 1, y = 2, z = 3; a = 10, b = 200, c = 300

The values and keyword can also be overridden by later function as follows −

julia> ABC(1, 2, 3; b = 1000_000, options...)
x = 1, y = 2, z = 3; a = 10, b = 200, c = 300

julia> ABC(1, 2, 3; options..., b= 1000_000)
x = 1, y = 2, z = 3; a = 10, b = 1000000, c = 300
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