Swift - Arrays

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Swift 4 arrays are used to store ordered lists of values of the same type. Swift 4 puts strict checking which does not allow you to enter a wrong type in an array, even by mistake.

If you assign a created array to a variable, then it is always mutable, which means you can change it by adding, removing, or changing its items; but if you assign an array to a constant, then that array is immutable, and its size and contents cannot be changed.

Creating Arrays

You can create an empty array of a certain type using the following initializer syntax −

var someArray = [SomeType]()

Here is the syntax to create an array of a given size a* and initialize it with a value −

var someArray = [SomeType](count: NumbeOfElements, repeatedValue: InitialValue)

You can use the following statement to create an empty array of Int type having 3 elements and the initial value as zero −

var someInts = [Int](count: 3, repeatedValue: 0)

Following is one more example to create an array of three elements and assign three values to that array −

var someInts:[Int] = [10, 20, 30]

Accessing Arrays

You can retrieve a value from an array by using subscript syntax, passing the index of the value you want to retrieve within square brackets immediately after the name of the array as follows −

var someVar = someArray[index]

Here, the index starts from 0 which means the first element can be accessed using the index as 0, the second element can be accessed using the index as 1 and so on. The following example shows how to create, initialize, and access arrays −

var someInts = [Int](count: 3, repeatedValue: 10)

var someVar = someInts[0]
print( "Value of first element is \(someVar)" )
print( "Value of second element is \(someInts[1])" )
print( "Value of third element is \(someInts[2])" )

When the above code is compiled and executed, it produces the following result −

Value of first element is 10
Value of second element is 10
Value of third element is 10

Modifying Arrays

You can use append() method or addition assignment operator (+=) to add a new item at the end of an array. Take a look at the following example. Here, initially, we create an empty array and then add new elements into the same array −

var someInts = [Int]()

someInts.append(20)
someInts.append(30)
someInts += [40]

var someVar = someInts[0]

print( "Value of first element is \(someVar)" )
print( "Value of second element is \(someInts[1])" )
print( "Value of third element is \(someInts[2])" )

When the above code is compiled and executed, it produces the following result −

Value of first element is 20
Value of second element is 30
Value of third element is 40

You can modify an existing element of an Array by assigning a new value at a given index as shown in the following example −

var someInts = [Int]()

someInts.append(20)
someInts.append(30)
someInts += [40]

// Modify last element
someInts[2] = 50

var someVar = someInts[0]

print( "Value of first element is \(someVar)" )
print( "Value of second element is \(someInts[1])" )
print( "Value of third element is \(someInts[2])" )

When the above code is compiled and executed, it produces the following result −

Value of first element is 20
Value of second element is 30
Value of third element is 50

Iterating Over an Array

You can use for-in loop to iterate over the entire set of values in an array as shown in the following example −

var someStrs = [String]()

someStrs.append("Apple")
someStrs.append("Amazon")
someStrs += ["Google"]
for item in someStrs {
   print(item)
}

When the above code is compiled and executed, it produces the following result −

Apple
Amazon
Google

You can use enumerate() function which returns the index of an item along with its value as shown below in the following example −

var someStrs = [String]()

someStrs.append("Apple")
someStrs.append("Amazon")
someStrs += ["Google"]

for (index, item) in someStrs.enumerated() {
   print("Value at index = \(index) is \(item)")
}

When the above code is compiled and executed, it produces the following result −

Value at index = 0 is Apple
Value at index = 1 is Amazon
Value at index = 2 is Google

Adding Two Arrays

You can use the addition operator (+) to add two arrays of the same type which will yield a new array with a combination of values from the two arrays as follows −

var intsA = [Int](count:2, repeatedValue: 2)
var intsB = [Int](count:3, repeatedValue: 1)

var intsC = intsA + intsB
for item in intsC {
   print(item)
}

When the above code is compiled and executed, it produces the following result −

2
2
1
1
1

The count Property

You can use the read-only count property of an array to find out the number of items in an array shown below −

var intsA = [Int](count:2, repeatedValue: 2)
var intsB = [Int](count:3, repeatedValue: 1)

var intsC = intsA + intsB

print("Total items in intsA = \(intsA.count)")
print("Total items in intsB = \(intsB.count)")
print("Total items in intsC = \(intsC.count)")

When the above code is compiled and executed, it produces the following result −

Total items in intsA = 2
Total items in intsB = 3
Total items in intsC = 5

The empty Property

You can use the read-only empty property of an array to find out whether an array is empty or not as shown below −

var intsA = [Int](count:2, repeatedValue: 2)
var intsB = [Int](count:3, repeatedValue: 1)
var intsC = [Int]()

print("intsA.isEmpty = \(intsA.isEmpty)")
print("intsB.isEmpty = \(intsB.isEmpty)")
print("intsC.isEmpty = \(intsC.isEmpty)")

When the above code is compiled and executed, it produces the following result −

intsA.isEmpty = false
intsB.isEmpty = false
intsC.isEmpty = true