The filtering function

Play audio slide show -- Keyboard shortcut: 'x'

Lecture overview -- Keyboard shortcut: 'u'

Previous page: Filtering -- Keyboard shortcut: 'p'

Next page: Examples of filtering -- Keyboard shortcut: 'n'

Lecture notes - all slides together

Annotated slide -- Keyboard shortcut: 't'

Textbook -- Keyboard shortcut: 'v'

Alphabetic index

Help page about these notes

Higher-order Functions - slide 12 : 34

The filtering function

For practical purposes it is important to have a memory efficient filter function

(define (filter pred lst)
  (reverse (filter-help pred lst '())))

(define (filter-help pred lst res)
  (cond ((null? lst) res)
        ((pred (car lst)) 
           (filter-help pred (cdr lst)  (cons (car lst) res)))
        (else 
           (filter-help pred (cdr lst)  res))))

A straightforward filter function