Lisp - Vector Functions

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LISP provides multiple functions on Vectors. In this chapter, we're discussing various functions available in LISP to work on vectors.

Modify elements of a vector

We can use setf in conjunction with aref or svref functions to modify required value. fill method can be used to update all values in one statement.

Using setf with aref function

aref is a generic function to work with generic vectors.

; define a vector of 3 elements with given list of values
(defvar my-vector (make-array 3 :initial-contents '(1 2 3)))

; print the vector
(print my-vector)

; modify third value of Vector
(setf (aref my-vector 2) 20)

(terpri)
; print the vector
(print my-vector)

Output

When you execute the code, it returns the following result −

#(1 2 3) 
#(1 2 20) 

Using setf with svref function

svref is a specifc function to work with simple vectors.

; define a vector of 3 numbers
(defvar my-vector (vector 1 2 3))

; print the vector
(print my-vector)

; modify third value of Vector
(setf (aref my-vector 2) 20)

(terpri)
; print the vector
(print my-vector)

Output

When you execute the code, it returns the following result −

#(1 2 3) 
#(1 2 20) 

Using fill function

fill function can be used to reset all values of a vector as shown below.

; define a vector of 3 numbers
(defvar my-vector (vector 1 2 3))

; print the vector
(print my-vector)

; reset all values to 0
(fill my-vector 0)

(terpri)
; print the vector
(print my-vector)

Output

When you execute the code, it returns the following result −

#(1 2 3) 

#(0 0 0) 

Accessing Information of a vector

We can use length function to get length of a vector. array-dimensions is a generic function to get size of the array and can be used to get the length of the vector. array-element-type function can be used to get the type of elements of specialized vectors.

main.lisp

; define a vector of 3 elements with given list of values
(defvar my-vector (make-array 3 :initial-contents '(1 2 3)))

; print the vector
(print my-vector)

; print length of the Vector
(print (length my-vector))

(terpri)
; print the dimension of vector
(print (array-dimensions my-vector))

(terpri)
; print the element type of vector
(print (array-element-type my-vector))

Output

When you execute the code, it returns the following result −

#(1 2 3) 
3 
(3) 
T 

Vector Operations

Following are examples of various useful functions to manipulate vectors.

Copy vectors using copy-seq function

; define a vector of 3 elements with given list of values
(defvar my-vector (make-array 3 :initial-contents '(1 2 3)))

; print the vector
(print my-vector)

; copy vector
(defvar copied-vector (copy-seq my-vector))

(terpri)
; print the vector
(print copied-vector)

Output

When you execute the code, it returns the following result −

#(1 2 3) 
#(1 2 3) 

Get sub-vector of vectors using subseq function

; define a vector of 6 elements with given list of values
(defvar my-vector (make-array 6 :initial-contents '(1 2 3 4 5 6)))

; print the vector
(print my-vector)

; get sub vector from index 1 to index 4(excluding)
(defvar sub-vector (subseq my-vector 1 4))

(terpri)
; print the vector
(print sub-vector)

Output

When you execute the code, it returns the following result −

#(1 2 3 4 5 6) 
#(2 3 4) 

Modifying each element of vector using map function

; define a vector of 6 elements with given list of values
(defvar my-vector (make-array 6 :initial-contents '(1 2 3 4 5 6)))

; print the vector
(print my-vector)

; double all elements of vector
(defvar updated-vector(map 'vector #'(lambda (x) (* x 2)) my-vector))

(terpri)
; print the vector
(print updated-vector)

Output

When you execute the code, it returns the following result −

#(1 2 3 4 5 6) 
#(2 4 6 8 10 12) 

Reducing elements of vector to one using reduce function

; define a vector of 6 elements with given list of values
(defvar my-vector (make-array 6 :initial-contents '(1 2 3 4 5 6)))

; print the vector
(print my-vector)

; get sum of all elements of the vector
(defvar sum (reduce #'+ my-vector))

(terpri)
; print the sum
(print sum)

Output

When you execute the code, it returns the following result −

#(1 2 3 4 5 6) 
21