map-extraction-with-get.md

Map extraction with get

(count {:firstname "Sally" :lastname "Brown"})
;=> 2

Every collection has a count function. Why do you think the answer is two? count is returning the number of associations.

Since map is a key-value pair, the key is used to get a value from a map.

get is a function that returns the value for a given key.

If the key does not exist, then a nil value is returned.

(get {:firstname "Sally" :lastname "Brown"} :firstname)
;=> "Sally"
(get {:firstname "Sally"} :lastname)
;=> nil

Note::

()

---

A default value can be included with the get function, so if a key is not found in the map, that default value is returned.

In this example we add the string "Unknown" to the get function call. That string is returned when the key we asked for is not in the map.

(get {:firstname "Sally"} :lastname "Unknown")
;=> "Unknown"

Note::

()

---

Hint::

When a key is a keyword then that keyword can be used as a function to lookup values in a map. (:firstname {:firstname "Sally" :lastname "Brown"})

A map can also act like a function when given a keyword as an argument ({:firstname "Sally" :lastname "Brown"} :firstname)

Both of the above work exactly as the get function, so if you don't quite follow this then stick with get.