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Data Structures - Vector

Creating a vector

(vector 5 10 15)
[1 2 3 4 5]
[56.9 60.2 61.8 63.1 54.3 66.4 66.5 68.1 70.2 69.2 63.1 57.1]
[]

Functions for vectors

(vector? [5 10 15])
;=> true

(vector 5 10 15)
;=> [5 10 15]

(conj [5 10] 15)
;=> [5 10 15]

(count [5 10 15])
;=> 3

(nth [5 10 15] 1)
;=> 10

(first [5 10 15])
;=> 5

Data Structures2 - Keyword, Maps

Creating a map

{:first "Sally" :last "Brown"}
{:a 1 :b "two"}
{}

Functions for Maps

; determine if value is a map
(map? {:first "Sally" :last "Brown"})
;=> true

; using keyword :first get the value
(get {:first "Sally" :last "Brown"} :first)
;=> "Sally"

; using keyword :first get the value and return :MISS if key doesn't exist in map
(get {:first "Sally"} :last :MISS)
;=> :MISS

; add a key/value to the map
(assoc {:first "Sally"} :last "Brown")
;=> {:first "Sally", :last "Brown"}

; remove (disassociate) the key/value of :last
(dissoc {:first "Sally" :last "Brown"} :last)
;=> {:first "Sally"}

; merge two maps
(merge {:first "Sally"} {:last "Brown"})
;=> {:first "Sally", :last "Brown"}

; get number of key/value pairs in this map
(count {:first "Sally" :last "Brown"})
;=> 2

; get all the keys in this map
(keys {:first "Sally" :last "Brown"})
;=> (:first :last)

; get all the values in this map
(vals {:first "Sally" :last "Brown"})
;=> ("Sally" "Brown")

Defining Functions

(defn function-name
  "description of function, optional"
  [param1 param2]
  (function-body))
  • Functions that return true or false--called predicates--usually end in ?
  • map and reduce - Functions that take other functions

Map and Reduce

; apply a function to every element in a collection
(map inc [1 2 3 4])
;=> (2 3 4 5)
; Similar to [(inc 1) (inc 2) (inc 3) (inc 4)]

map takes a function and a collection, then applies the function to each element in the collection in order. It returns the new collection.

; reduce a collection to one value using a function
(reduce + [1 3 5 7])
;=> 16
; Similar to (+ 1 3) ;=> 4
;            (+ 4 5) ;=> 9
;            (+ 9 7) ;=> 16

reduce takes a function and a collection. First, it applies the function to the first element and the second element, then it applies the function to the result of that, plus the third element. It continues rolling up the results until it gets to the last thing in the collection.

Flow Control

(if conditional-expression
  expression-to-evaluate-when-true
  expression-to-evaluate-when-false)

Boolean logic with and, or and not

x y (and x y) (or x y) (not x) (not y)
false false false false true true
true false false true false true
true true true true false false
false true false true true false

let

Assigning names to values inside of functions

(let [first-name (:first-name user)            ; assign to `first-name`
      message (str "Hello, " first-name "!")]  ; assign to `message`
  (println message))                           ; do something with `message`