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;; @@PLEAC@@_2.1 Checking Whether a String Is a Valid Number
(import '(java.text NumberFormat ParseException)
'(java.util Locale))
(def locale Locale/US)
(defn nb [s]
(let [nf (NumberFormat/getInstance locale)]
(.parse nf s)))
;; user=> (nb "100")
;; 100
;; user=> (nb "not a number")
;; java.text.ParseException: Unparseable number: "not a number"
;; (def s1 "100")
;; (def s1 "not a number")
(Integer/parseInt s1)
(catch NumberFormatException _ex
(println (str s1 " is not an integer"))))
;; (def s2 3.14)
;; (def s2 "foo")
(Float/parseFloat s2)
(catch NumberFormatException _ex
(println (str s2 " is not a float"))))
(defn isNumeric [s]
(let [nf (NumberFormat/getInstance locale)]
(.parse nf s)
(catch ParseException _ex false))))
;; @@PLEAC@@_2.2 Comparing Floating-Point Numbers
;; (equal NUM1 NUM2 ACCURACY) returns true if NUM1 and NUM2 are
;; equal to ACCURACY number of decimal places
;; jli for mbac: not sure if you can use with-precision for this:
(defn equal [num1 num2 accuracy]
(letfn [(bignum [num]
(.setScale (BigDecimal. num)
(= 0 (.compareTo (bignum num1) (bignum num2)))))
;; with a scaling factor
;; use "M" suffix for BigDecimal literals
(def wage 5.36M)
(def hours 40M)
(def week (.multiply wage hours))
(println (str "One week's wage is: $" week))
;; One week's wage is: $214.40
;; @@PLEAC@@_2.3 Rounding Floating-Point Numbers
;; (def unrounded ...)
;; (def scale ...)
;; (def roundingMode ...)
(def rounded (.setScale unrounded scale roundingMode))
(def a 0.255M)
(def b (.setScale a 2 BigDecimal/ROUND_HALF_UP))
(println (str "Unrounded: " a))
(println (str "Rounded: " b))
;=> Unrounded: 0.255
;=> Rounded: 0.26
;; caution, Math.rint() rounds to the nearest integer!
(def a [3.3 3.5 3.7 -3.3])
(println "number\tint\tfloor\ceil")
(map (fn [x] (println (str (Math/rint x) "\t" (Math/floor x) "\t" (Math/ceil x)))) a)
;; 3.0 3.0 4.0
;; 4.0 3.0 4.0
;; 4.0 3.0 4.0
;; -3.0 -4.0 -3.0
;; @@PLEAC@@_2.4 Converting Between Binary and Decimal
(def i (Integer/parseInt s 2))
(def s (Integer/toString i 2))
;; reader supports "<radix>r<number>"
(def i 2r0110110) ; i = 54
(def s (Integer/toString 54 2)) ; s = 110110
;; @@PLEAC@@_2.5 Operating on a Series of Integers
(let [x 1 y 10]
(doseq [i (range x (inc y))]
;; i is set to every integer from X to Y inclusive
(let [x 1 y 10]
(doseq [i (range x (+ y 1) 7)]
;; i is set to every integer from X to Y, stepsize = 7
(apply println (cons "Infancy is:" (range 0 3)))
(apply println (cons "Toddling is:" (range 3 5)))
(apply println (cons "Childhood is:" (range 5 13)))
;; Infancy is: 0 1 2
;; Toddling is: 3 4
;; Childhood is: 5 6 7 8 9 10 11 12
;; @@PLEAC@@_2.6 Working with Roman Numerals
;; no roman module available
;; @@PLEAC@@_2.7 Generating Random Numbers
(import '(java.util Random))
(def random (Random. ))
(def i (+ (.nextInt random (- y (+ x 1))) x))
(def i (+ (.nextInt random 51) 25))
(println i)
;; @@PLEAC@@_2.8 Generating Different Random Numbers
;; Seed the generator with an integer
(Random. 5)
;; Use SecureRandom instead to seed with bytes from stdin
(import '( SecureRandom))
;; jli for mbac: unqualified "use" is almost always ungood. use :only
;; or :rename.
;; mbac: fixed!
(use '[ :only (to-byte-array)])
(SecureRandom. (to-byte-array System/in))
;; @@PLEAC@@_2.9 Making Numbers Even More Random
(let [srng (SecureRandom.)
buf (byte-array 10)]
(.nextBytes srng buf)
;; @@PLEAC@@_2.10 Generating Biased Random Numbers
(def prng (Random.))
(defn gaussian-rand []
(let [[w u1 u2] (loop []
(let [u1 (- (* 2 (.nextDouble prng)) 1)
u2 (- (* 2 (.nextDouble prng)) 1)
w (+ (* u1 u1) (* u2 u2))]
(if (>= w 1)
[w u1 u2])))
w (Math/sqrt (* -2 (/ (Math/log w) w)))
g2 (* u1 w)
g1 (* u2 w)]
;; -----------------------------
;; weight-to-dist: takes a list of pairs mapping key to weight and
;; returns a list of pairs mapping key to probability
(defn weight-to-dist [weights]
(let [total (apply + (map (fn [[_key weight]] weight) weights))]
(map (fn [[key weight]] [key (/ weight total)])
;; weighted-rand: takes a list of pairs mapping key to probability
;; and returns the corresponding key
(defn weighted-rand [dist]
;; accumulate without mutation
(let [go (fn cont [p lst]
(if-let [[key weight] (first lst)]
(let [pp (- p weight)]
(if (< pp 0)
[pp key]
(recur pp (rest lst))))))
result (go (.nextDouble (Random.)) dist)]
;; to avoid floating point inaccuracies
(if (nil? result)
(recur dist)
(let [[_p key] result]
(def mean 25)
(def stddev 2)
(def salary (+ (* (gaussian-rand) stddev) mean))
(printf "You have been hired at $%.2f\n" salary)
;; @@PLEAC@@_2.11 Doing Trigonometry in Degrees, not Radians
(defn radians [deg] (Math/toRadians deg))
(defn degrees [rad] (Math/toDegrees rad))
(defn sin-deg [deg] (Math/sin (radians deg)))
;; @@PLEAC@@_2.12 Calculating More Trigonometric Functions
(defn tan [theta] (/ (Math/sin theta) (Math/cos theta)))
;; or use Math/tan
(def y
(tan (/ Math/PI 2))
(catch Exception e nil)))
;; @@PLEAC@@_2.13 Taking Logarithms
(defn log_e [x] (Math/log x))
(defn log_10 [x] (Math/log10 x))
(defn log-base [base value] (/ (log_e value) (log_e base)))
(def answer (log-base 10 10000))
(printf "log10(10,000) = %f" answer)
;; @@PLEAC@@_2.14 Multiplying Matrices
;; This is a very academic, purely functional implementation of
;; multiply-matrix. A performance critical implementation would
;; likely not use Clojure's immutable vectors.
(defn multiply-matrix [m1 m2]
(let [dim (fn [m] [(count m) (count (first m))])
[r1 c1] (dim m1)
[r2 c2] (dim m2)]
(if (not (= c1 r2))
nil ; matrix dimensions don't match
(let [dot-product (fn [v1 v2]
(reduce (fn [a i] (+ a (* (nth v1 i) (nth v2 i))))
(range 0 (count v1))))
row (fn [m i] (nth m i))
col (fn [m i] (map (fn [r] (nth (nth m r) i))
(range (count m))))]
(map (fn [r]
(map (fn [c] (dot-product (row m1 r) (col m2 c)))
(range 0 c2)))
(range 0 r1))))))
;; @@PLEAC@@_2.15 Using Complex Numbers
;; c = a * b manually
(defrecord Complex [real imag])
(defn mul [a b]
(Complex. (* (.real a) (.real b))
(* (.imag a) (.imag b))))
;; c = a * b using the complex-numbers module
(use '(clojure.contrib complex-numbers)
'(clojure.contrib.generic [arithmetic :only [+ *]]
[math-functions :only [sqrt]]))
(def a (complex 3 5))
(def b (complex 2 -2))
(def c (* a b))
(def c (* (complex 3 5) (complex 2 -2))) ; or on one line
(defn print-complex-sqrt [x]
(let [as-string (fn [c] (format "%s+%si"
(real c)
(if (= (imag c) 1) "" (imag c))))]
(printf "sqrt(%s) = %s\n"
(as-string x)
(as-string (sqrt x)))))
(def d (complex 3 4))
(print-complex-sqrt d)
;; @@PLEAC@@_2.16 Converting Between Octal and Hexadecimal
;; hex and octal should not have leading 0x or 0 characters
(defn hex-and-oct-as-decs [hex octal]
(let [dec-of-hex (Integer/parseInt hex 16)
dec-of-oct (Integer/parseInt octal 8)]
;; use dec-of-hex and dec-of-oct here
(let [num (->
(print "Gimme a number in decimal, octal, or hex: ")
(printf "%s %s %s\n"
(Integer/toString num)
(Integer/toOctalString num)
(Integer/toHexString num)))
;; @@PLEAC@@_2.17 Putting Commas in Numbers
(import '(java.text NumberFormat)
'(java.util Locale))
(def locale Locale/US)
(defn commify-localized [num]
(let [nf (NumberFormat/getInstance locale)]
(.format nf num)))
;; deck version
(defn commify-hipster [numstr]
(->> (.toString numstr)
(partition-all 3)
(interpose \,)
(apply str)))
;; @@PLEAC@@_2.18 Printing Correct Plurals
(defn print-plurals [hours centuries]
(printf "It took %d hour%s\n" hours (if (= hours 1) "" "s"))
(printf "%d hour%s %s enough.\n"
(if (= hours 1) "" "s")
(if (= hours 1) "is" "are"))
(printf "It took %d centur%s\n" centuries (if (= centuries 1) "y" "ies"))))
(def noun-rules
[[#"ss$" "sses"]
[#"ph$" "phes"]
[#"sh$" "shes"]
[#"ch$" "ches"]
[#"z$" "zes"]
[#"ff$" "ffs"]
[#"f$" "ves"]
[#"ey$" "eys"]
[#"y$" "ies"]
[#"ix$" "ices"]
[#"s$" "ses"]
[#"x$" "xes"]
[#"$" "s"]])
(require '(clojure.contrib [str-utils2 :as s]))
(defn noun_plural [word]
(some (fn [[re ending]]
(if (re-find re word) (s/replace word re ending)))
(def verb_singular noun_plural) ; make function alias
;; Note: there's no perl Lingua::EN::Inflect equivalent module
;; @@PLEAC@@_2.19 Program: Calculating Prime Factors
;; jli for mbac: shouldn't this return {orig 1} for prime numbers?
;; mbac for jli: maybe, but the perl version doesn't do this either
(defn get-factors [orig]
(letfn [(factor-out [n factors i]
(if (zero? (mod n i))
(recur (/ n i)
(assoc factors i (inc (factors i 0)))
[n factors]))]
(loop [i 2
sqi 4
[n factors] [orig {}]]
(<= sqi n) (recur (inc i)
(+ sqi (* 2 i) 1)
(factor-out n factors i))
(and (not= n 1)
(not= n orig)) (assoc factors n (inc (factors n 0)))
:default factors))))
(defn print-factors [orig factors]
(let [head (format "%-10d" orig)
lines (if (zero? (count factors))
(map (fn [[f e]] (format "%d^%d" f e)) factors))
s (apply str (interpose "\n" (cons head lines)))]
(println s)))
(loop [i 0]
(if (< i (count *command-line-args*))
(let [n (Integer/parseInt (.get argv i))]
(print-factors n (factorize n))
(recur (inc i))))))