Swift Dictionary filter()

var marks = ["Sabby": 89, "Dabby": 45, "Cathy": 74]

// return all the key-value pair with value greater than 50 
var result = marks.filter({ $0.value > 50})

print(result)

// Output: ["Cathy": 74, "Sabby": 89]

filter() Syntax

The syntax of the filter() method is:

dictionary.filter({condition})

Here, dictionary is an object of the Dictionary class.

filter() Parameters

The filter() method takes one parameter:

• condition - a closure that accepts a condition and returns a Bool value.

filter() Return Value

• returns a new dictionary with all the elements from dictionary that satisfy the provided condition

Example 1: Swift dictionary filter()

var age = ["Kyle": 7, "Eric": 9, "Kenny": 10]

// return all key-value pairs with value that start with "K"
var result = age.filter( { $0.key.hasPrefix("K") } )

print(result) 

Output

["Nepal", "Norwegian"]

In the above program, notice the closure definition,

{ $0.key.hasPrefix("K") }

This is a short-hand closure that checks whether all the keys in the dictionary have the prefix "K" or not.

$0 is the shortcut to mean the first parameter passed into the closure.

The closure returns a Bool value depending upon the condition. If the condition is

• true - the dictionary key-value pair is kept
• false - the dictionary key-value pair is dropped/omitted

And finally, all the elements that start with "N" are stored in the result variable.

Example 2: Return Only Even Values From dictionary

var numbers = ["1st": 2, "2nd": 7, "3rd": 4, "4th": 5]

// check if all values are even numbers or not 
var result = numbers.filter({ $0.value % 2 == 0 })

print(result)

Output

["1st": 2, "3rd": 4]