Swift Tutorials

How to Set a Default Value for a Key in a Dictionary in Swift

How to Set a Default Value for a Key in a Dictionary in Swift ?

Answer

To set a default value for a key in a dictionary in Swift, you can check if the key exists and if not, set a default value. Swift dictionaries do not have a built-in method like `setdefault` in Python, so you need to handle it manually.

✐ Examples

1 Setting a Default Value for a Key Using `if` Statement

We can set a default value for a key in a dictionary in Swift by checking if the key exists and setting a default value if it does not. This example demonstrates how to check for a key and set a default value.

For example,

We start by declaring and initializing a dictionary named myDictionary with integer keys and string values.
We check if a key exists using an `if` statement.
If the key does not exist, we set a default value for the key.
We print the dictionary contents to verify the key-value pairs.

Swift Program

var myDictionary: [Int: String] = [:]

// Key to check
let keyToCheck = 1

// Default value to set if key does not exist
let defaultValue = "Default"

// Check if the key exists and set default value if it does not
if myDictionary[keyToCheck] == nil {
    myDictionary[keyToCheck] = defaultValue
}

// Print the dictionary contents
print("Dictionary contents:")
for (key, value) in myDictionary {
    print("Key: \(key), Value: \(value)")
}

Output

Dictionary contents:
Key: 1, Value: Default

2 Setting a Default Value for Multiple Keys Using a Helper Method

We can create a helper method to set a default value for multiple keys in a dictionary in Swift. This example demonstrates how to use a helper method to set default values for keys.

For example,

We start by declaring and initializing a dictionary named myDictionary with integer keys and string values.
We create a helper method named setDefaultValue to set default values for keys.
We use the helper method to set default values for multiple keys.
We print the dictionary contents to verify the key-value pairs.

Swift Program

var myDictionary: [Int: String] = [:]

// Helper method to set default value
func setDefaultValue(for key: Int, in dictionary: inout [Int: String], to defaultValue: String) {
    if dictionary[key] == nil {
        dictionary[key] = defaultValue
    }
}

// Set default values for multiple keys
setDefaultValue(for: 1, in: &myDictionary, to: "DefaultOne")
setDefaultValue(for: 2, in: &myDictionary, to: "DefaultTwo")

// Print the dictionary contents
print("Dictionary contents:")
for (key, value) in myDictionary {
    print("Key: \(key), Value: \(value)")
}

Output

Dictionary contents:
Key: 1, Value: DefaultOne
Key: 2, Value: DefaultTwo

Summary

In this tutorial, we learned How to Set a Default Value for a Key in a Dictionary in Swift language with well detailed examples.

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How to Set a Default Value for a Key in a Dictionary in Swift