How to use the keys method in Clojure

In Clojure, the keys method returns a sequence of the map's keys in the same order as they are defined.

The syntax of this method is as follows:

s = (keys input_map)

This function accepts as a parameter the map to be processed input_map.
This function returns a sequence s of the input_map keys.

Let's look at the following examples to understand this method better:

Example 1

The example below demonstrates how to collect the keys of a map hosting the information of an employee:

(def employee {:name "Adrian" :age 30 :salary 30})
(print "The employee hashmap's info:" employee )
(print "\nThe keys of the employee hashmap's info are:" (keys employee))

Explanation

Let's look at the code widget above:

  • Line 1: Define a map containing employee information and assign it to a value named employee.

  • Line 2: Display a message showing the map already defined.

  • Line 3: Invoke the keys method to extract the map keys and print them out.

Example 2

The example below shows how to apply the keys method on an empty map: 

(def employee {})
(print "The employee hashmap's info:" employee )
(print "\nThe keys of the employee hashmap's info are:" (keys employee))

Explanation

Let's explain the code widget above:

  • Line 1: We define an empty map.

  • Line 2: We display a message showing the map previously defined.

  • Line 3: We invoke the keys method to extract the map keys and print them out. We'll notice that a nil (null or absence of value) is returned since the specified map is empty.

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