Making comparison in Clojure - clojure

Developed a function in Clojure to check if inputs for the :maxlength and :minlength is 1-3 characters long and the text in associated column is within the range of min and max. Is there a cleaner way to do this? I'd appreciate if a more efficient method is suggested especially the if form.
(defn range-text-length
"input = {:col val :minlength minlength :maxlength maxlength}
Expects 3 parameter key/value combinations:
:col The column containing the text value
:maxlength integer value greater than zero up to 3 characters long
Catch any rows where the column contains text that is shorter than the Minimum Length or longer than the Maximum Length"
[row input]
(let [{:keys [col minlength maxlength ]} input
minlength-count (count (str minlength))
maxlength-count (count (str maxlength))
max (read-string (str maxlength))
min (read-string (str minlength))]
(if (and (and (> maxlength-count 0) (<= maxlength-count 3) (number? max) (> max 0))
(and (> minlength-count 0)(<= minlength-count 3)(number? min)(> min 0)))
(and (>= (count (get row col)) min) (<= (count (get row col)) max))
(throw (Exception. "length must be a positive integer value with no more than 3 digits.")))))
And I call the function thus:
(catch-out-of-range-text-length ["weert" "sertt" "qwertyuiopasdfg" "asert"] {:col 2 :minlength 2 :maxlength 15})

I think the following is equivalent to yours:
(defn range-text-length [row input]
(let [in-range? (fn [n] (< 0 n 1000))
{:keys [col minlength maxlength ]} input
]
(if (every? in-range? [minlength maxlength])
(<= minlength (count (row col)) maxlength)
(throw (Exception. "length must be a positive integer with no more than 3 digits.")))))

First off: nested and is redundant. Since the code can't differentiate which part of the condition was false, there is no effect of nested calls to and as opposed to putting all the clauses in the same and.
Next, <, <=, >, and >= all take a variable number of arguments, and with a bit of refactoring you can combine calls that share a term.
Finally, rather than testing if something is greater than 0, you can directly test if it is positive with pos?.
(defn range-text-length
"input = {:col val :minlength minlength :maxlength maxlength}
Expects 3 parameter key/value combinations:
:col The column containing the text value
:maxlength integer value greater than zero up to 3 characters long
Catch any rows where the column contains text that is shorter than the Minimum Length or longer than the Maximum Length"
[row input]
(let [{:keys [col minlength maxlength ]} input
minlength-count (count (str minlength))
maxlength-count (count (str maxlength))
max (read-string (str maxlength))
min (read-string (str minlength))]
(if (and (> 4 maxlength-count 0)
(number? max)
(pos? max)
(> 4 minlength-count 0)
(number? min)
(pos? min))
(>= max (count (get row col)) min)
(throw (Exception. "length must be a positive integer value with no more than 3 digits.")))))

I see you've already marked #noisesmith as answer. Whilst that was going on I was toying around and produced the following:
(defn range-text-length
[row {:keys [col minlength maxlength] :as input}]
(if-let [x (and (and (pos? minlength) (< minlength 1000))
(and (pos? maxlength) (< maxlength 1000))
(and (>= (count (get row col)) minlength)
(<= (count (get row col)) maxlength)))]
true
(throw (Exception. "length must be a positive integer value with no more than 3 digits."))))
Despite the variadic capability of and I separated for readability.
EDIT: Did away with the if-let:
(defn range-text-length
[row {:keys [col minlength maxlength] :as input}]
(or (and (and (pos? minlength) (< minlength 1000))
(and (pos? maxlength) (< maxlength 1000))
(and (>= (count (get row col)) minlength)
(<= (count (get row col)) maxlength)))
(throw (Exception. "length must be a positive integer value with no more than 3 digits."))))

if clause tidied up and preconditions used to avoid polluting the real purpose of the function with the assumed preconditions. Some extra examples
(defn range-text-length
"input = {:col val :minlength minlength :maxlength maxlength}
Expects 3 parameter key/value combinations:
:col The column containing the text value
:maxlength integer value greater than zero up to 3 characters long
Catch any rows where the column contains text that is shorter than the Minimum Length or longer than the Maximum Length"
[row input]
{: pre [(let [{:keys [col minlength maxlength ]} input
minlength-count (count (str minlength))
maxlength-count (count (str maxlength))
max (read-string (str maxlength))
min (read-string (str minlength))
crc (count (get row col))]
(not (and (pos? maxlength-count)
(pos? minlength-count)
(pos? max)
(pos? min)
(<= maxlength-count 3)
(<= minlength-count 3)
(>= crc min)
(<= crc max))))]}
(do (println "do my stuff with satisfied preconditions")))

Related

Return an else value when using recur

I am new to Clojure, and doing my best to forget all my previous experience with more procedural languages (java, ruby, swift) and embrace Clojure for what it is. I am actually really enjoying the way it makes me think differently -- however, I have come up against a pattern that I just can't seem to figure out. The easiest way to illustrate, is with some code:
(defn char-to-int [c] (Integer/valueOf (str c)))
(defn digits-dont-decrease? [str]
(let [digits (map char-to-int (seq str)) i 0]
(when (< i 5)
(if (> (nth digits i) (nth digits (+ i 1)))
false
(recur (inc i))))))
(def result (digits-dont-decrease? "112233"))
(if (= true result)
(println "fit rules")
(println "doesn't fit rules"))
The input is a 6 digit number as a string, and I am simply attempting to make sure that each digit from left to right is >= the previous digit. I want to return false if it doesn't, and true if it does. The false situation works great -- however, given that recur needs to be the last thing in the function (as far as I can tell), how do I return true. As it is, when the condition is satisfied, I get an illegal argument exception:
Execution error (IllegalArgumentException) at clojure.exercise.two/digits-dont-decrease? (four:20).
Don't know how to create ISeq from: java.lang.Long
How should I be thinking about this? I assume my past training is getting in my mental way.
This is not answering your question, but also shows an alternative. While the (apply < ...) approach over the whole string is very elegant for small strings (it is eager), you can use every? for an short-circuiting approach. E.g.:
user=> (defn nr-seq [s] (map #(Integer/parseInt (str %)) s))
#'user/nr-seq
user=> (every? (partial apply <=) (partition 2 1 (nr-seq "123")))
true
You need nothing but
(apply <= "112233")
Reason: string is a sequence of character and comparison operator works on character.
(->> "0123456789" (mapcat #(repeat 1000 %)) (apply str) (def loooong))
(count loooong)
10000
(time (apply <= loooong))
"Elapsed time: 21.006625 msecs"
true
(->> "9123456789" (mapcat #(repeat 1000 %)) (apply str) (def bad-loooong))
(count bad-loooong)
10000
(time (apply <= bad-loooong))
"Elapsed time: 2.581750 msecs"
false
(above runs on my iPhone)
In this case, you don't really need loop/recur. Just use the built-in nature of <= like so:
(ns tst.demo.core
(:use demo.core tupelo.core tupelo.test))
(def true-samples
["123"
"112233"
"13"])
(def false-samples
["10"
"12324"])
(defn char->int
[char-or-str]
(let [str-val (str char-or-str)] ; coerce any chars to len-1 strings
(assert (= 1 (count str-val)))
(Integer/parseInt str-val)))
(dotest
(is= 5 (char->int "5"))
(is= 5 (char->int \5))
(is= [1 2 3] (mapv char->int "123"))
; this shows what we are going for
(is (<= 1 1 2 2 3 3))
(isnt (<= 1 1 2 1 3 3))
and now test the char sequences:
;-----------------------------------------------------------------------------
; using built-in `<=` function
(doseq [true-samp true-samples]
(let [digit-vals (mapv char->int true-samp)]
(is (apply <= digit-vals))))
(doseq [false-samp false-samples]
(let [digit-vals (mapv char->int false-samp)]
(isnt (apply <= digit-vals))))
if you want to write your own, you can like so:
(defn increasing-equal-seq?
"Returns true iff sequence is non-decreasing"
[coll]
(when (< (count coll) 2)
(throw (ex-info "coll must have at least 2 vals" {:coll coll})))
(loop [prev (first coll)
remaining (rest coll)]
(if (empty? remaining)
true
(let [curr (first remaining)
prev-next curr
remaining-next (rest remaining)]
(if (<= prev curr)
(recur prev-next remaining-next)
false)))))
;-----------------------------------------------------------------------------
; using home-grown loop/recur
(doseq [true-samp true-samples]
(let [digit-vals (mapv char->int true-samp)]
(is (increasing-equal-seq? digit-vals))))
(doseq [false-samp false-samples]
(let [digit-vals (mapv char->int false-samp)]
(isnt (increasing-equal-seq? digit-vals))))
)
with result
-------------------------------
Clojure 1.10.1 Java 13
-------------------------------
Testing tst.demo.core
Ran 2 tests containing 15 assertions.
0 failures, 0 errors.
Passed all tests
Finished at 23:36:17.096 (run time: 0.028s)
You an use loop with recur.
Assuming you require following input v/s output -
"543221" => false
"54321" => false
"12345" => true
"123345" => true
Following function can help
;; Assuming char-to-int is defined by you before as per the question
(defn digits-dont-decrease?
[strng]
(let [digits (map char-to-int (seq strng))]
(loop [;;the bindings in loop act as initial state
decreases true
i (- (count digits) 2)]
(let [decreases (and decreases (>= (nth digits (+ i 1)) (nth digits i)))]
(if (or (< i 1) (not decreases))
decreases
(recur decreases (dec i)))))))
This should work for numeric string of any length.
Hope this helps. Please let me know if you were looking for something else :).
(defn non-decreasing? [str]
(every?
identity
(map
(fn [a b]
(<= (int a) (int b)))
(seq str)
(rest str))))
(defn non-decreasing-loop? [str]
(loop [a (seq str) b (rest str)]
(if-not (seq b)
true
(if (<= (int (first a)) (int (first b)))
(recur (rest a) (rest b))
false))))
(non-decreasing? "112334589")
(non-decreasing? "112324589")
(non-decreasing-loop? "112334589")
(non-decreasing-loop? "112324589")

Idiomatic Creation of Hash-Map

I'd like to create a hash-map that has n number of key-value pairs created in sets of 3 where the sets do not intersect, e.g. [(34 false) (35 false) (36 false)] && [(24 false) (25 false) (26 false)] -> {34 false 35 false 36 false 24 false 25 false 26 false}
EDIT:
To play/practice with Clojure, I'm attempting to implement an idiomatic version of the battleship board game. I decided to store the battleship coordinates in a hash-map where the keys are coordinates and the values are booleans indicating whether that section of the ship has been hit. The specific piece of code below is supposed to
Select an axis (horizontal or vertical)
Select a coordinate for the bow of the ship
"Build" the rest of the ship (3 coordinates in total) by increasing the x or y value accordingly, e.g. {"10" false "11" false "12" false}. Note the "10" translates into the second row of a matrix, first column.
Note: Before adding the ship to the hash-map of coordinates the new ship coordinates must be checked to ensure that an intersection does not exist. If it does, the ship must be "re-built."
To that end, I've created the code below. It has 2 issues:
Executing the function results in the following exception from the use of the 'acc' accumulator:
clojure.lang.LazySeq cannot be cast to clojure.lang.Associative
The result of the function is not a single hash-map, but rather a list of n hash-maps
Using idiomatic clojure, how can I achieve my goal?
(defn launch
[n]
(loop [cnt n acc {}]
(if (= cnt 0)
acc
(recur
(- cnt 1)
((fn []
(let [axis (rand-int 2)]
(if (= axis 0)
(let [x (rand-int 8) y (rand-int 10)]
(for [k (range 3)]
(assoc acc (str y (+ x k)) false)))
(let [x (rand-int 10) y (rand-int 8)]
(for [k (range 3)]
(assoc acc (str (+ y k) x) false)))))))))))
that's how i would rewrite it:
(defn create-key [axis-val i]
(if axis-val
(str (rand-int 10) (+ (rand-int 8) i))
(str (+ (rand-int 8) i) (rand-int 10))))
(defn launch [n]
(reduce (fn [acc axis]
(reduce #(assoc % (create-key axis %2) false)
acc
(range 3)))
{}
(repeatedly n #(zero? (rand-int 2)))))
in repl:
user> (launch 5)
{"40" false, "07" false, "19" false,
"46" false, "87" false, "47" false,
"41" false, "62" false, "86" false}
or (in case you don't like reduce):
(defn launch [n]
(zipmap (mapcat #(map (partial create-key %) (range 3))
(repeatedly n #(zero? (rand-int 2))))
(repeat false)))
the third variant is to use list comprehension to generate keys:
(defn launch [n]
(zipmap (for [_ (range n)
:let [axis (zero? (rand-int 2))]
i (range 3)]
(create-key axis i))
(repeat false)))
all three of them are idiomatic ones, i guess, so it's up to you to choose one, according to your own preferred programming style.
notice that the resulting keys are shuffled inside the map, because unsorted maps don't preserve order. If it is important, you should use sorted-map
What about your variant, the one generating error is this:
(for [k (range 3)] (assoc acc (str y (+ x k)) false))
it doesn't put all the keys to one map, rather it generates a seq of three items equalling (assoc acc k false):
(let [acc {}]
(for [k (range 3)] (assoc acc k false)))
;;=> ({0 false} {1 false} {2 false})
to do what you want, you use reduce:
(let [acc {}]
(reduce #(assoc %1 %2 false) acc (range 3)))
;;=> {0 false, 1 false, 2 false}
leetwinski has given a more concise answer, but I thought I would post this anyway, since I basically left your structure intact, and this may help you see the error a bit more clearly.
First, I am not sure why you were rebinding acc to the value of an anonymous function call. Your let will happily return a result; so, you should probably do some thinking about why you thought it was necessary to create an anonymous function.
Second, the problem is that for returns a lazy seq, and you are binding this to what you think is a map data structure. This explains why it works fine for cases 0 and 1, but when you use a value of 2 it fails.
Since I don't really fully understand what you're trying to accomplish, here is your original code, modified to work. Disclaimer--this is not really idiomatic and not how I would write it, but I'm posting because it may be helpful to see versus the original, since it actually works.
(defn launch
[n]
(loop [cnt n
acc {}]
(if (= cnt 0)
acc
(recur
(dec cnt)
(into acc
(let [axis (rand-int 2)]
(if (= axis 0)
(let [x (rand-int 8) y (rand-int 10)]
(map #(hash-map (str y (+ x %)) false) (range 3)))
(let [x (rand-int 10) y (rand-int 8)]
(map #(hash-map (str (+ y %) x) false) (range 3))))))))))

clojure performance on badly performing code

I have completed this problem on hackerrank and my solution passes most test cases but it is not fast enough for 4 out of the 11 test cases.
My solution looks like this:
(ns scratch.core
(require [clojure.string :as str :only (split-lines join split)]))
(defn ascii [char]
(int (.charAt (str char) 0)))
(defn process [text]
(let [parts (split-at (int (Math/floor (/ (count text) 2))) text)
left (first parts)
right (if (> (count (last parts)) (count (first parts)))
(rest (last parts))
(last parts))]
(reduce (fn [acc i]
(let [a (ascii (nth left i))
b (ascii (nth (reverse right) i))]
(if (> a b)
(+ acc (- a b))
(+ acc (- b a))))
) 0 (range (count left)))))
(defn print-result [[x & xs]]
(prn x)
(if (seq xs)
(recur xs)))
(let [input (slurp "/Users/paulcowan/Downloads/input10.txt")
inputs (str/split-lines input)
length (read-string (first inputs))
texts (rest inputs)]
(time (print-result (map process texts))))
Can anyone give me any advice about what I should look at to make this faster?
Would using recursion instead of reduce be faster or maybe this line is expensive:
right (if (> (count (last parts)) (count (first parts)))
(rest (last parts))
(last parts))
Because I am getting a count twice.
You are redundantly calling reverse on every iteration of the reduce:
user=> (let [c [1 2 3]
noisey-reverse #(doto (reverse %) println)]
(reduce (fn [acc e] (conj acc (noisey-reverse c) e))
[]
[:a :b :c]))
(3 2 1)
(3 2 1)
(3 2 1)
[(3 2 1) :a (3 2 1) :b (3 2 1) :c]
The reversed value could be calculated inside the containing let, and would then only need to be calculated once.
Also, due to the way your parts is defined, you are doing linear time lookups with each call to nth. It would be better to put parts in a vector and do indexed lookup. In fact you wouldn't need a reversed parts, and could do arithmetic based on the count of the vector to find the item to look up.

How to split a number in Clojure?

I am looking for a nice method to split a number with n digits in Clojure I have these two methods:
(->> (str 942)
seq
(map str)
(map read-string)) => (9 4 2)
and...
(defn digits [n]
(cons
(str (mod n 10)) (lazy-seq (positive-numbers (quot n 10)))))
(map read-string (reverse (take 5 (digits 10012)))) => (1 0 0 1 2)
Is there a more concise method for doing this type of operation?
A concise version of your first method is
(defn digits [n]
(->> n str (map (comp read-string str))))
... and of your second is
(defn digits [n]
(if (pos? n)
(conj (digits (quot n 10)) (mod n 10) )
[]))
An idiomatic alternative
(defn digits [n]
(->> n
(iterate #(quot % 10))
(take-while pos?)
(mapv #(mod % 10))
rseq))
For example,
(map digits [0 942 -3])
;(nil (9 4 2) nil)
The computation is essentially eager, since the last digit in is the
first out. So we might as well use mapv and rseq (instead of map and reverse) to do it faster.
The function is transducer-ready.
It works properly only on positive numbers.
You could simply do
(map #(Character/digit % 10) (str 942))
EDIT: Adding a function definition
(defn digits [number] (map #(Character/digit % 10) (str number)))
Usage:
(digits 1234)
Note: This is concise, but does use java String and Character classes. An efficient implementation can be written using integer modulo arithmetic, but won't be concise. One such solution similar to Charles' answer would be:
(defn numTodigits
[num]
(loop [n num res []]
(if (zero? n)
res
(recur (quot n 10) (cons (mod n 10) res)))))
Source
I'm not sure about concise, but this one avoids unnecessary inefficiency such as converting to strings and back to integers.
(defn digits [n]
(loop [result (list), n n]
(if (pos? n)
(recur (conj result (rem n 10))
(quot n 10))
result)))
A recursive implementation (could be more efficient and less concise, but it shouldn't matter for reasonable numbers).
(defn digits [n]
(when (pos? n)
(concat (digits (quot n 10))
[(mod n 10)])))
a looping method:
(defn split-numbers [number]
(loop [itr 0 res [] n number]
(if (= n 0)
res
(recur (inc itr) (concat (vector (mod n 10)) res) (int (/ n 10)))
)
)
)
Easiest i could find:
(->> (str n)
seq
(map (comp read-string str)))

How to properly indent clojure/lisp?

I want to indent the following piece of code.
How would a lisper indent this?
I am especially confused about where to put newlines.
(defn primes [n]
(letfn [(sieve [table removal]
(assoc table removal false))
(primebools [i table]
(cond
(= i n) table
(table i) (recur (inc i)
(reduce sieve
table
(range (* i i) n i)))
:else (recur (inc i)
table)))]
(let [prime? (primebools 2 (apply vector (repeat n true)))]
(filter prime? (range 2 n)))))
(defn primes [n]
(letfn [(sieve [table removal]
(assoc table removal false))
(primebools [i table]
(cond
(= i n) table
(table i) (recur (inc i)
(reduce sieve table
(range (* i i) n i)))
:else (recur (inc i) table)))]
(let [prime? (primebools 2 (apply vector (repeat n true)))]
(filter prime? (range 2 n)))))
Is how I would do it.
In addition to #dnolen's answer, I usually put a new line when there's
a new function (like your first two lines)
to indent long or important argument to a function (like the cond block)
logically keep each line to less than 80 characters and break up long ideas to smaller chunks
most importantly, be consistent!
Then just align and indent lines so that the identations are for the same depth of code.