Clojure's Composite Data Structures (L16) Flashcards
What are Clojure’s 4 primary data structures?
Maps, vectors, lists, sets.
Clojure maps are equivalent to which Python datastructure?
Dictionaries.
How are empty maps defined?
{}
In practice, strings are used as Clojure keys.
False - keywords (:label) are often used as map keys.
Are Clojure’s :keywords case sensitive?
Yes.
Why are :keywords used over strings as map keys?
Faster internal lookups.
What Clojure function is used to perform map lookups?
get
Write 2 different ways in which the :key keyword is used to obtain a value from a map labelled m1.
(get m1 :key)
(:key m1)
What function is used to concisely retrieve values from nested maps?
get-in
What does the following line do?
(get jobs :bill “x”)
Returns :bill’s value in the jobs map, or returns “x” if not found.
Can non keyword keys also be used in the following manner?
(:bill jobs “x”)
No, only keywords may because as function invocations.
What does the following return?
(keys m1)
(vals m1)
A list of m1s keys and values, respectively.
What Clojure function can be used to check for the existence of a key in a map?
(contains? m1 :k)
When are commas used in Clojure?
Commas are considered to be whitespace. They may be used to make code slightly more readable.
Vectors in Clojure are 0-indexed sequences.
True.
In what two ways can vectors be created in Clojure?
[1 2 3]
(vector 1 2 3)
What functions are used to retrieve vector data at a given index?
get or nth.
Clojure generates an error when access to a vectors out of bounds index is attempted.
False - nil is returned instead.
Functions can be put in Clojure vectors.
True.
In what two ways can lists be created in Clojure?
‘(1 2 3)
(list 1 2 3)
Below is a valid list.
‘(+ 2 2)
True.
Below is a valid list.
(2 2 2)
False.
Clojure lists have indexing.
False.
What functions can be used to access list elements by their position?
nth, but not get.
Clojure generates an error when access to a lists out of bounds position is attempted.
True.
What is generally faster, nth on a list or get on a vector?
get on an unmodified vector is O(1), whereas nth on a list is O(n).
In what two ways can sets be created in Clojure?
#{1 2 3}
(hash-set 1 2 3)
Which Clojure function removes the duplicates from a set?
There aren’t any, as sets will automatically discard duplicates.
How can we create sets from existing lists and vectors?
(set ‘(1 1 2 2)) &
(set [1 1 2 2])
What are the three ways of searching for an element in a set?
(get s1 val)
(:val s1)
(contains? s1 val)
What does the following return, if s1 is a set that doesn’t contain 4?
(get s1 4)
nil
What does the following return, if s1 is a set that contains :val?
(:val s1)
:val (it returns itself).
What Clojure function adds a value to a sequence?
conj
(conj [1 2 3] 4) returns [1 2 3 4].
True.
(conj ‘(1 2 3) 4) returns ‘(1 2 3 4).
False - it returns ‘(4 1 2 3).
What is returned by the following?
(assoc [1 2 3] 1 0)
[1 0 3]
What happens when a “change” is made to a vector?
A new path-like data structure is created, which reference the original vector’s (tree) indexing structure.
What is the complexity of accessing an index on a modified vector?
O(log n)
If Clojure’s vector’s were augmented with index structures that weren’t kept balanced, would access time still be logarithmic?
No.
