Clojure's Composite Data Structures (L16)

Question 1

What are Clojure’s 4 primary data structures?

Answer 1

Maps, vectors, lists, sets.

Question 2

Clojure maps are equivalent to which Python datastructure?

Answer 2

Dictionaries.

Question 3

How are empty maps defined?

Answer 3

{}

Question 4

In practice, strings are used as Clojure keys.

Answer 4

False - keywords (:label) are often used as map keys.

Question 5

Are Clojure’s :keywords case sensitive?

Answer 5

Yes.

Question 6

Why are :keywords used over strings as map keys?

Answer 6

Faster internal lookups.

Question 7

What Clojure function is used to perform map lookups?

Answer 7

get

Question 8

Write 2 different ways in which the :key keyword is used to obtain a value from a map labelled m1.

Answer 8

(get m1 :key)
(:key m1)

Question 9

What function is used to concisely retrieve values from nested maps?

Answer 9

get-in

Question 10

What does the following line do?
(get jobs :bill “x”)

Answer 10

Returns :bill’s value in the jobs map, or returns “x” if not found.

Question 11

Can non keyword keys also be used in the following manner?
(:bill jobs “x”)

Answer 11

No, only keywords may because as function invocations.

Question 12

What does the following return?
(keys m1)
(vals m1)

Answer 12

A list of m1s keys and values, respectively.

Question 13

What Clojure function can be used to check for the existence of a key in a map?

Answer 13

(contains? m1 :k)

Question 14

When are commas used in Clojure?

Answer 14

Commas are considered to be whitespace. They may be used to make code slightly more readable.

Question 15

Vectors in Clojure are 0-indexed sequences.

Answer 15

True.

Question 16

In what two ways can vectors be created in Clojure?

Answer 16

[1 2 3]
(vector 1 2 3)

Question 17

What functions are used to retrieve vector data at a given index?

Answer 17

get or nth.

Question 18

Clojure generates an error when access to a vectors out of bounds index is attempted.

Answer 18

False - nil is returned instead.

Question 19

Functions can be put in Clojure vectors.

Answer 19

True.

Question 20

In what two ways can lists be created in Clojure?

Answer 20

‘(1 2 3)
(list 1 2 3)

Question 21

Below is a valid list.
‘(+ 2 2)

Answer 21

True.

Question 22

Below is a valid list.
(2 2 2)

Answer 22

False.

Question 23

Clojure lists have indexing.

Answer 23

False.

Question 24

What functions can be used to access list elements by their position?

Answer 24

nth, but not get.

Question 25

Clojure generates an error when access to a lists out of bounds position is attempted.

Answer 25

True.

Question 26

What is generally faster, nth on a list or get on a vector?

Answer 26

get on an unmodified vector is O(1), whereas nth on a list is O(n).

Question 27

In what two ways can sets be created in Clojure?

Answer 27

#{1 2 3}
(hash-set 1 2 3)

Question 28

Which Clojure function removes the duplicates from a set?

Answer 28

There aren’t any, as sets will automatically discard duplicates.

Question 29

How can we create sets from existing lists and vectors?

Answer 29

(set ‘(1 1 2 2)) &
(set [1 1 2 2])

Question 30

What are the three ways of searching for an element in a set?

Answer 30

(get s1 val)
(:val s1)
(contains? s1 val)

Question 31

What does the following return, if s1 is a set that doesn’t contain 4?
(get s1 4)

Answer 31

nil

Question 32

What does the following return, if s1 is a set that contains :val?
(:val s1)

Answer 32

:val (it returns itself).

Question 33

What Clojure function adds a value to a sequence?

Answer 33

conj

Question 34

(conj [1 2 3] 4) returns [1 2 3 4].

Answer 34

True.

Question 35

(conj ‘(1 2 3) 4) returns ‘(1 2 3 4).

Answer 35

False - it returns ‘(4 1 2 3).

Question 36

What is returned by the following?
(assoc [1 2 3] 1 0)

Answer 36

[1 0 3]

Question 37

What happens when a “change” is made to a vector?

Answer 37

A new path-like data structure is created, which reference the original vector’s (tree) indexing structure.

Question 38

What is the complexity of accessing an index on a modified vector?

Answer 38

O(log n)

Question 39

If Clojure’s vector’s were augmented with index structures that weren’t kept balanced, would access time still be logarithmic?

Answer 39

No.