A first attempt at creating bayesian a spam filter from stratch; Trying to do this in lisp as a learning exercise; Definitely still a work in progress...

spam.clisp

;; A first attempt at creating bayesian a spam filter from stratch
;; Trying to do this in lisp as a learning exercise
;; Definitely still a work in progress...

(defparameter *spam* '(this is a spam document that is fake news))
(defparameter *ham* '(this is nikhils document))
(defparameter *testdoc* '(this is a test document that is meant to be fake))
(setq spam-table (make-hash-table))
(setq ham-table (make-hash-table))

# count the words
(defun count-words(hashds corpus)
    (mapcar (lambda(x)
                (princ x)
                (if (gethash x hashds)
                    (setf (gethash x hashds) (+ 1 (gethash x hashds)))
                    (setf (gethash x hashds) 1)
                )
            )
            corpus
    )
)

(count-words spam-table *SPAM*)
(count-words ham-table *HAM*)

(defun nbayes(ws s wh h)
    ;;P(S|W) = P(W|S)*P(S) / ( P(W|S)*P(S) + P(W|H)*P(H) )
    (if
        (not (eq 0 (+ (* ws s) (* wh h))))
    (/
        (* ws s)
        (+ (* ws s) (* wh h))
    ))
)

(defun getfreq(word table)
    (/
        (if (gethash word table)
            (gethash word table)
            0
        )
        (hash-table-count table)
    )
)

(getfreq 'THIS spam-table)
(getfreq 'THIS ham-table)

(nbayes (getfreq 'THIS spam-table) 0.5  (getfreq 'THIS ham-table) 0.5)

(defun posterior(word prob-spam prob-ham)
    ;; prevent divison by zero by checking word before use
    (unless (eq (nbayes (getfreq word spam-table) prob-spam  (getfreq word ham-table) prob-ham) nil)
        "NO CAN DO"
        (nbayes (getfreq word spam-table) prob-spam  (getfreq word ham-table) prob-ham)
    )
)

(posterior 'FAKE 0.5 0.5)
(posterior 'DOCUMENT 0.2 0.8)
(posterior 'NIKHILS 0.8 0.2)
(posterior 'THIS 0.2 0.8)

;; What I need is another hash that has all words used over both documents as keys, and frequencies as values

(defun print-hash-entry (key value)
    (format t "The value associated with the key ~S is ~S~%" key value))
(maphash #'print-hash-entry spam-table)

(defun getkeys(key value)
    (key)
)

(maphash #'getkeys spam-table)


(cons (gethash x spam-table) (gethash x ham-table) )

;;(/ (* p1 p2 p3 p4 p5 p6 pn..) (+ (p1 p2 p3 p4 p5 p6 pn..) ((- p1 1) (- p2 1) (- p3 1))) )

(*
    (remove nil (mapcar (lambda(x)
                (posterior x 0.5 0.5)
            )
            *testdoc*
        )
    )
)