Clojure Koans: Vectors


Learning all about vectors in this episode. They are very similar to lists but have some key differences that Richard Hickey deemed necessary. Lets get started!

lein koan run
“You can use vectors in clojure as array-like structures”
(= __ (count [42]))

1

“You can create a vector from a list”
(= __ (vec ‘(1)))

[1]

“Or from some elements”
(= __ (vector nil nil))

[nil nil]

Thats an interesting vector.

“But you can populate it with any number of elements at once”
(= [1 __] (vec ‘(1 2)))

vec: Creates a new vector containing the contents of coll. Java arrays will be aliased and should not be modified.

[1 2]

“Conjoining to a vector is different than to a list”
(= __ (conj [111 222] 333))

[111 222 333]

Vectors will join to the back while lists will conjoin to the front.

“You can get the first element of a vector like so”
(= __ (first [:peanut :butter :and :jelly]))

:peanut

“And the last in a similar fashion”
(= __ (last [:peanut :butter :and :jelly]))

:jelly

“Or any index if you wish”
(= __ (nth [:peanut :butter :and :jelly] 3))

:jelly

“You can also slice a vector”
(= __ (subvec [:peanut :butter :and :jelly] 1 3))

[:butter :and]

subvec: Returns a persistent vector of items in vector from start to end.

subvec does not include the last index.

“Equality with collections is in terms of values”
(= (list 1 2 3) (vector 1 2 __)))

3

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