Five functions to get the digits of a number












0















I'm writing a simple function: given a number, it will return a sequence or a collection of the digits in the number (in the correct order). i.e (get-digits-fn 1234567) => (1 2 3 4 5 6 7) / [1 2 3 4 5 6 7]



Below are five attempts at the same function:



(defn get-digits-1 [num]
(->> [num '()]
(iterate (fn [[num digits]]
(when (> num 0)
[(quot num 10) (conj digits (rem num 10))])))
(take-while some?)
(last)
(second)))

(defn get-digits-2 [num]
(when (> num 0)
(lazy-seq (concat (get-digits-2 (quot num 10)) '((rem num 10))))))

;; Suggested by Carcigenate
(defn get-digits-3 [num]
(->> (str)
(map str)
(map int)
(into '())))

(defn get-digits-4 [num]
(loop [n num
res '()]
(if (= n 0)
res
(recur (quot n 10) (conj res (rem n 10))))))

(defn get-digits-5 [num]
(->>
(iterate (fn [[n digits]]
[(quot n 10) (conj digits (rem n 10))])
[num '()])
(drop-while #(not= 0 (first %)))
(first)
(second)))


A helper function for testing performance:



(defn quick-bench-get-digits [fn range]
(quick-bench (->> range
(map fn)
(map (partial apply vector))
(into ))))


The perf results (output truncated to only show execution time mean):



eul> (quick-bench-get-digits get-digits-1 (range 1 100000))
Execution time mean : 129.516521 ms

eul> (quick-bench-get-digits get-digits-2 (range 1 100000))
Execution time mean : 128.637055 ms

eul> (quick-bench-get-digits get-digits-3 (range 1 100000))
Execution time mean : 24.267716 ms

eul> (quick-bench-get-digits get-digits-4 (range 1 100000))
Execution time mean : 25.083393 ms

eul> (quick-bench-get-digits get-digits-5 (range 1 100000))
Execution time mean : 145.430443 ms


It looks like get-digits-3 is the fastest while get-digits-4 is closely behind. (As the numbers increase, get-digits-3 outperforms get-digits-4. i.e try (range 1000000 2000000))




  1. Any way to increase performance more without leaving Clojure land?

  2. If mutability and Java inter-op is allowed, is there a way to increase performance?


p.s. functions 1 and 5 are almost identical. This was incremental exploration.










share|improve this question

























  • Is performance of this code specifically really a concern? I'm doubtful that this is what would be the choking point of the program. 24ms is very fast, especially for an inflated test case.

    – Carcigenicate
    Nov 9 '18 at 17:59


















0















I'm writing a simple function: given a number, it will return a sequence or a collection of the digits in the number (in the correct order). i.e (get-digits-fn 1234567) => (1 2 3 4 5 6 7) / [1 2 3 4 5 6 7]



Below are five attempts at the same function:



(defn get-digits-1 [num]
(->> [num '()]
(iterate (fn [[num digits]]
(when (> num 0)
[(quot num 10) (conj digits (rem num 10))])))
(take-while some?)
(last)
(second)))

(defn get-digits-2 [num]
(when (> num 0)
(lazy-seq (concat (get-digits-2 (quot num 10)) '((rem num 10))))))

;; Suggested by Carcigenate
(defn get-digits-3 [num]
(->> (str)
(map str)
(map int)
(into '())))

(defn get-digits-4 [num]
(loop [n num
res '()]
(if (= n 0)
res
(recur (quot n 10) (conj res (rem n 10))))))

(defn get-digits-5 [num]
(->>
(iterate (fn [[n digits]]
[(quot n 10) (conj digits (rem n 10))])
[num '()])
(drop-while #(not= 0 (first %)))
(first)
(second)))


A helper function for testing performance:



(defn quick-bench-get-digits [fn range]
(quick-bench (->> range
(map fn)
(map (partial apply vector))
(into ))))


The perf results (output truncated to only show execution time mean):



eul> (quick-bench-get-digits get-digits-1 (range 1 100000))
Execution time mean : 129.516521 ms

eul> (quick-bench-get-digits get-digits-2 (range 1 100000))
Execution time mean : 128.637055 ms

eul> (quick-bench-get-digits get-digits-3 (range 1 100000))
Execution time mean : 24.267716 ms

eul> (quick-bench-get-digits get-digits-4 (range 1 100000))
Execution time mean : 25.083393 ms

eul> (quick-bench-get-digits get-digits-5 (range 1 100000))
Execution time mean : 145.430443 ms


It looks like get-digits-3 is the fastest while get-digits-4 is closely behind. (As the numbers increase, get-digits-3 outperforms get-digits-4. i.e try (range 1000000 2000000))




  1. Any way to increase performance more without leaving Clojure land?

  2. If mutability and Java inter-op is allowed, is there a way to increase performance?


p.s. functions 1 and 5 are almost identical. This was incremental exploration.










share|improve this question

























  • Is performance of this code specifically really a concern? I'm doubtful that this is what would be the choking point of the program. 24ms is very fast, especially for an inflated test case.

    – Carcigenicate
    Nov 9 '18 at 17:59
















0












0








0








I'm writing a simple function: given a number, it will return a sequence or a collection of the digits in the number (in the correct order). i.e (get-digits-fn 1234567) => (1 2 3 4 5 6 7) / [1 2 3 4 5 6 7]



Below are five attempts at the same function:



(defn get-digits-1 [num]
(->> [num '()]
(iterate (fn [[num digits]]
(when (> num 0)
[(quot num 10) (conj digits (rem num 10))])))
(take-while some?)
(last)
(second)))

(defn get-digits-2 [num]
(when (> num 0)
(lazy-seq (concat (get-digits-2 (quot num 10)) '((rem num 10))))))

;; Suggested by Carcigenate
(defn get-digits-3 [num]
(->> (str)
(map str)
(map int)
(into '())))

(defn get-digits-4 [num]
(loop [n num
res '()]
(if (= n 0)
res
(recur (quot n 10) (conj res (rem n 10))))))

(defn get-digits-5 [num]
(->>
(iterate (fn [[n digits]]
[(quot n 10) (conj digits (rem n 10))])
[num '()])
(drop-while #(not= 0 (first %)))
(first)
(second)))


A helper function for testing performance:



(defn quick-bench-get-digits [fn range]
(quick-bench (->> range
(map fn)
(map (partial apply vector))
(into ))))


The perf results (output truncated to only show execution time mean):



eul> (quick-bench-get-digits get-digits-1 (range 1 100000))
Execution time mean : 129.516521 ms

eul> (quick-bench-get-digits get-digits-2 (range 1 100000))
Execution time mean : 128.637055 ms

eul> (quick-bench-get-digits get-digits-3 (range 1 100000))
Execution time mean : 24.267716 ms

eul> (quick-bench-get-digits get-digits-4 (range 1 100000))
Execution time mean : 25.083393 ms

eul> (quick-bench-get-digits get-digits-5 (range 1 100000))
Execution time mean : 145.430443 ms


It looks like get-digits-3 is the fastest while get-digits-4 is closely behind. (As the numbers increase, get-digits-3 outperforms get-digits-4. i.e try (range 1000000 2000000))




  1. Any way to increase performance more without leaving Clojure land?

  2. If mutability and Java inter-op is allowed, is there a way to increase performance?


p.s. functions 1 and 5 are almost identical. This was incremental exploration.










share|improve this question
















I'm writing a simple function: given a number, it will return a sequence or a collection of the digits in the number (in the correct order). i.e (get-digits-fn 1234567) => (1 2 3 4 5 6 7) / [1 2 3 4 5 6 7]



Below are five attempts at the same function:



(defn get-digits-1 [num]
(->> [num '()]
(iterate (fn [[num digits]]
(when (> num 0)
[(quot num 10) (conj digits (rem num 10))])))
(take-while some?)
(last)
(second)))

(defn get-digits-2 [num]
(when (> num 0)
(lazy-seq (concat (get-digits-2 (quot num 10)) '((rem num 10))))))

;; Suggested by Carcigenate
(defn get-digits-3 [num]
(->> (str)
(map str)
(map int)
(into '())))

(defn get-digits-4 [num]
(loop [n num
res '()]
(if (= n 0)
res
(recur (quot n 10) (conj res (rem n 10))))))

(defn get-digits-5 [num]
(->>
(iterate (fn [[n digits]]
[(quot n 10) (conj digits (rem n 10))])
[num '()])
(drop-while #(not= 0 (first %)))
(first)
(second)))


A helper function for testing performance:



(defn quick-bench-get-digits [fn range]
(quick-bench (->> range
(map fn)
(map (partial apply vector))
(into ))))


The perf results (output truncated to only show execution time mean):



eul> (quick-bench-get-digits get-digits-1 (range 1 100000))
Execution time mean : 129.516521 ms

eul> (quick-bench-get-digits get-digits-2 (range 1 100000))
Execution time mean : 128.637055 ms

eul> (quick-bench-get-digits get-digits-3 (range 1 100000))
Execution time mean : 24.267716 ms

eul> (quick-bench-get-digits get-digits-4 (range 1 100000))
Execution time mean : 25.083393 ms

eul> (quick-bench-get-digits get-digits-5 (range 1 100000))
Execution time mean : 145.430443 ms


It looks like get-digits-3 is the fastest while get-digits-4 is closely behind. (As the numbers increase, get-digits-3 outperforms get-digits-4. i.e try (range 1000000 2000000))




  1. Any way to increase performance more without leaving Clojure land?

  2. If mutability and Java inter-op is allowed, is there a way to increase performance?


p.s. functions 1 and 5 are almost identical. This was incremental exploration.







performance comparative-review clojure






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Nov 9 '18 at 4:39









200_success

129k15152414




129k15152414










asked Nov 9 '18 at 3:47









nakiyanakiya

1165




1165













  • Is performance of this code specifically really a concern? I'm doubtful that this is what would be the choking point of the program. 24ms is very fast, especially for an inflated test case.

    – Carcigenicate
    Nov 9 '18 at 17:59





















  • Is performance of this code specifically really a concern? I'm doubtful that this is what would be the choking point of the program. 24ms is very fast, especially for an inflated test case.

    – Carcigenicate
    Nov 9 '18 at 17:59



















Is performance of this code specifically really a concern? I'm doubtful that this is what would be the choking point of the program. 24ms is very fast, especially for an inflated test case.

– Carcigenicate
Nov 9 '18 at 17:59







Is performance of this code specifically really a concern? I'm doubtful that this is what would be the choking point of the program. 24ms is very fast, especially for an inflated test case.

– Carcigenicate
Nov 9 '18 at 17:59












1 Answer
1






active

oldest

votes


















1














I'm afraid your code has errors, so your benchmarking is invalid.




  • The get-digits-3 function is wrong.

  • A corrected version runs about twelve times slower than
    get-digits-4.


Repairing get-digits-3



Your get-digits-3 doesn't work:



=> (get-digits-3 123456789)
()


The function chain should be applied to the argument num:



(defn get-digits-3 [num]
(->> num
(str)
(map str)
(map int)
(into '())))


But this fails:



=> (get-digits-3 123456789)
ClassCastException java.base/java.lang.String cannot be cast to java.base/java.lang.Character clojure.lang.RT.intCast (RT.java:1213)


The culprit is the (map int) line. You can't apply int to strings. If you drop the offending line, you get the character values:



=> (get-digits-3 123456789)
(57 56 55 54 53 52 51 50 49)


Notice, too, that they are in reverse order. So we




  • subtract the value of character 0 and


  • conj onto the other end by using a vector.


This gives us ...



(defn get-digits-3 [num]
(->> num
(str)
(map int)
(map #(- % (int )))
(into )))

=> (get-digits-3 123456789)
[1 2 3 4 5 6 7 8 9]


Benchmarking



I went about this differently:




  • I used a single example instead of a range.

  • I used Criterium's bench rather than its quick-bench.


The results were as follow:



For your original (faulty) version of get-digits-3:



=> (bench (get-digits-3 123456789))
...
Execution time mean : 228.998292 ns


For the corrected version:



=> (bench (get-digits-3 123456789))
...
Execution time mean : 3.440024 µs


And for get-digits-4:



=>(bench (get-digits-4 123456789))
...
Execution time mean : 247.502418 ns


This confirms that your faulty get-digits-3 is about as fast as get-digits-4. And get-digits-3 ignores its argument, so is bound to get relatively faster as the numbers get bigger. You can see that the corrected version is nowhere near competitive.






share|improve this answer


























  • 3 µs / 250ns is about twelve times slower, not a hundred times. I think you lost an order of magnitude somewhere.

    – Toby Speight
    yesterday











  • @TobySpeight Thanks. Corrected

    – Thumbnail
    6 hours ago











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1 Answer
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active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









1














I'm afraid your code has errors, so your benchmarking is invalid.




  • The get-digits-3 function is wrong.

  • A corrected version runs about twelve times slower than
    get-digits-4.


Repairing get-digits-3



Your get-digits-3 doesn't work:



=> (get-digits-3 123456789)
()


The function chain should be applied to the argument num:



(defn get-digits-3 [num]
(->> num
(str)
(map str)
(map int)
(into '())))


But this fails:



=> (get-digits-3 123456789)
ClassCastException java.base/java.lang.String cannot be cast to java.base/java.lang.Character clojure.lang.RT.intCast (RT.java:1213)


The culprit is the (map int) line. You can't apply int to strings. If you drop the offending line, you get the character values:



=> (get-digits-3 123456789)
(57 56 55 54 53 52 51 50 49)


Notice, too, that they are in reverse order. So we




  • subtract the value of character 0 and


  • conj onto the other end by using a vector.


This gives us ...



(defn get-digits-3 [num]
(->> num
(str)
(map int)
(map #(- % (int )))
(into )))

=> (get-digits-3 123456789)
[1 2 3 4 5 6 7 8 9]


Benchmarking



I went about this differently:




  • I used a single example instead of a range.

  • I used Criterium's bench rather than its quick-bench.


The results were as follow:



For your original (faulty) version of get-digits-3:



=> (bench (get-digits-3 123456789))
...
Execution time mean : 228.998292 ns


For the corrected version:



=> (bench (get-digits-3 123456789))
...
Execution time mean : 3.440024 µs


And for get-digits-4:



=>(bench (get-digits-4 123456789))
...
Execution time mean : 247.502418 ns


This confirms that your faulty get-digits-3 is about as fast as get-digits-4. And get-digits-3 ignores its argument, so is bound to get relatively faster as the numbers get bigger. You can see that the corrected version is nowhere near competitive.






share|improve this answer


























  • 3 µs / 250ns is about twelve times slower, not a hundred times. I think you lost an order of magnitude somewhere.

    – Toby Speight
    yesterday











  • @TobySpeight Thanks. Corrected

    – Thumbnail
    6 hours ago
















1














I'm afraid your code has errors, so your benchmarking is invalid.




  • The get-digits-3 function is wrong.

  • A corrected version runs about twelve times slower than
    get-digits-4.


Repairing get-digits-3



Your get-digits-3 doesn't work:



=> (get-digits-3 123456789)
()


The function chain should be applied to the argument num:



(defn get-digits-3 [num]
(->> num
(str)
(map str)
(map int)
(into '())))


But this fails:



=> (get-digits-3 123456789)
ClassCastException java.base/java.lang.String cannot be cast to java.base/java.lang.Character clojure.lang.RT.intCast (RT.java:1213)


The culprit is the (map int) line. You can't apply int to strings. If you drop the offending line, you get the character values:



=> (get-digits-3 123456789)
(57 56 55 54 53 52 51 50 49)


Notice, too, that they are in reverse order. So we




  • subtract the value of character 0 and


  • conj onto the other end by using a vector.


This gives us ...



(defn get-digits-3 [num]
(->> num
(str)
(map int)
(map #(- % (int )))
(into )))

=> (get-digits-3 123456789)
[1 2 3 4 5 6 7 8 9]


Benchmarking



I went about this differently:




  • I used a single example instead of a range.

  • I used Criterium's bench rather than its quick-bench.


The results were as follow:



For your original (faulty) version of get-digits-3:



=> (bench (get-digits-3 123456789))
...
Execution time mean : 228.998292 ns


For the corrected version:



=> (bench (get-digits-3 123456789))
...
Execution time mean : 3.440024 µs


And for get-digits-4:



=>(bench (get-digits-4 123456789))
...
Execution time mean : 247.502418 ns


This confirms that your faulty get-digits-3 is about as fast as get-digits-4. And get-digits-3 ignores its argument, so is bound to get relatively faster as the numbers get bigger. You can see that the corrected version is nowhere near competitive.






share|improve this answer


























  • 3 µs / 250ns is about twelve times slower, not a hundred times. I think you lost an order of magnitude somewhere.

    – Toby Speight
    yesterday











  • @TobySpeight Thanks. Corrected

    – Thumbnail
    6 hours ago














1












1








1







I'm afraid your code has errors, so your benchmarking is invalid.




  • The get-digits-3 function is wrong.

  • A corrected version runs about twelve times slower than
    get-digits-4.


Repairing get-digits-3



Your get-digits-3 doesn't work:



=> (get-digits-3 123456789)
()


The function chain should be applied to the argument num:



(defn get-digits-3 [num]
(->> num
(str)
(map str)
(map int)
(into '())))


But this fails:



=> (get-digits-3 123456789)
ClassCastException java.base/java.lang.String cannot be cast to java.base/java.lang.Character clojure.lang.RT.intCast (RT.java:1213)


The culprit is the (map int) line. You can't apply int to strings. If you drop the offending line, you get the character values:



=> (get-digits-3 123456789)
(57 56 55 54 53 52 51 50 49)


Notice, too, that they are in reverse order. So we




  • subtract the value of character 0 and


  • conj onto the other end by using a vector.


This gives us ...



(defn get-digits-3 [num]
(->> num
(str)
(map int)
(map #(- % (int )))
(into )))

=> (get-digits-3 123456789)
[1 2 3 4 5 6 7 8 9]


Benchmarking



I went about this differently:




  • I used a single example instead of a range.

  • I used Criterium's bench rather than its quick-bench.


The results were as follow:



For your original (faulty) version of get-digits-3:



=> (bench (get-digits-3 123456789))
...
Execution time mean : 228.998292 ns


For the corrected version:



=> (bench (get-digits-3 123456789))
...
Execution time mean : 3.440024 µs


And for get-digits-4:



=>(bench (get-digits-4 123456789))
...
Execution time mean : 247.502418 ns


This confirms that your faulty get-digits-3 is about as fast as get-digits-4. And get-digits-3 ignores its argument, so is bound to get relatively faster as the numbers get bigger. You can see that the corrected version is nowhere near competitive.






share|improve this answer















I'm afraid your code has errors, so your benchmarking is invalid.




  • The get-digits-3 function is wrong.

  • A corrected version runs about twelve times slower than
    get-digits-4.


Repairing get-digits-3



Your get-digits-3 doesn't work:



=> (get-digits-3 123456789)
()


The function chain should be applied to the argument num:



(defn get-digits-3 [num]
(->> num
(str)
(map str)
(map int)
(into '())))


But this fails:



=> (get-digits-3 123456789)
ClassCastException java.base/java.lang.String cannot be cast to java.base/java.lang.Character clojure.lang.RT.intCast (RT.java:1213)


The culprit is the (map int) line. You can't apply int to strings. If you drop the offending line, you get the character values:



=> (get-digits-3 123456789)
(57 56 55 54 53 52 51 50 49)


Notice, too, that they are in reverse order. So we




  • subtract the value of character 0 and


  • conj onto the other end by using a vector.


This gives us ...



(defn get-digits-3 [num]
(->> num
(str)
(map int)
(map #(- % (int )))
(into )))

=> (get-digits-3 123456789)
[1 2 3 4 5 6 7 8 9]


Benchmarking



I went about this differently:




  • I used a single example instead of a range.

  • I used Criterium's bench rather than its quick-bench.


The results were as follow:



For your original (faulty) version of get-digits-3:



=> (bench (get-digits-3 123456789))
...
Execution time mean : 228.998292 ns


For the corrected version:



=> (bench (get-digits-3 123456789))
...
Execution time mean : 3.440024 µs


And for get-digits-4:



=>(bench (get-digits-4 123456789))
...
Execution time mean : 247.502418 ns


This confirms that your faulty get-digits-3 is about as fast as get-digits-4. And get-digits-3 ignores its argument, so is bound to get relatively faster as the numbers get bigger. You can see that the corrected version is nowhere near competitive.







share|improve this answer














share|improve this answer



share|improve this answer








edited 6 hours ago

























answered Dec 13 '18 at 21:48









ThumbnailThumbnail

1,27657




1,27657













  • 3 µs / 250ns is about twelve times slower, not a hundred times. I think you lost an order of magnitude somewhere.

    – Toby Speight
    yesterday











  • @TobySpeight Thanks. Corrected

    – Thumbnail
    6 hours ago



















  • 3 µs / 250ns is about twelve times slower, not a hundred times. I think you lost an order of magnitude somewhere.

    – Toby Speight
    yesterday











  • @TobySpeight Thanks. Corrected

    – Thumbnail
    6 hours ago

















3 µs / 250ns is about twelve times slower, not a hundred times. I think you lost an order of magnitude somewhere.

– Toby Speight
yesterday





3 µs / 250ns is about twelve times slower, not a hundred times. I think you lost an order of magnitude somewhere.

– Toby Speight
yesterday













@TobySpeight Thanks. Corrected

– Thumbnail
6 hours ago





@TobySpeight Thanks. Corrected

– Thumbnail
6 hours ago


















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