Split string into multiple arrays fast

Question

I have 100,000 strings of length 10, which needs to be split in 9 ways as shown below

10 # the whole string
5 x 5 # 2 strings of length 5 each
4 x 6 # and so on...
6 x 4
3 x 3 x 4
3 x 4 x 3
4 x 3 x 3
3 x 7
7 x 3

So for example the string WGWJAWMPPJ would turn into

WGWJAWMPPJ
WGWJA WMPPJ
WGWJ AWMPPJ
WGWJAW MPPJ
WGW JAW MPPJ
WGW JAWM PPJ
WGWJ AWM PPJ
WGW JAWMPPJ
WGWJAWM PPJ

The code I wrote is below

def breakdown(str)
  [
    [str],
    [str[0..4], str[5..9]],
    [str[0..3], str[4..9]],
    [str[0..5], str[6..9]],
    [str[0..2], str[3..5], str[6..9]],
    [str[0..2], str[3..6], str[7..9]],
    [str[0..3], str[4..6], str[7..9]],
    [str[0..2], str[3..9]],
    [str[0..6], str[7..9]]
  ]
end

Is there any way to improve the performance of the above method?

My money is on "no". I'm curious: why do you want to do that and why do you need better performance? I'd think your code would split 100,000 strings in the blink of an eye. — Cary Swoveland
– Cary Swoveland, Commented Sep 8, 2019 at 6:01
You'll end up with a lot of substring creation and copying. You might want to try this on an implementation like Rubinius, which AFAIK uses ropes instead of strings to implement the String class. The operations you are performing, are what ropes are very good at. — Jörg W Mittag
– Jörg W Mittag, Commented Sep 8, 2019 at 6:31
do you need to return an array always or just a string output as you've shown in your sample output? — lacostenycoder
– lacostenycoder, Commented Sep 8, 2019 at 8:15
@CarySwoveland I was just curious whether there is a better way to do this — vishless
– vishless, Commented Sep 9, 2019 at 8:54

iGian · Accepted Answer · 2019-09-08 10:20:25Z

2

I suppose you could gain a bit of speed storing repetitive slices in variables:

def breakdown(str)
  s_0_2 = str[0..2]
  s_0_3 = str[0..3]
  s_6_9 = str[6..9]
  s_7_9 = str[7..9]
  [
    [str],
    [str[0..4], str[5..9]],
    [s_0_3, str[4..9]],
    [str[0..5], s_6_9],
    [s_0_2, str[3..5], s_6_9],
    [s_0_2, str[3..6], s_7_9],
    [s_0_3, str[4..6], s_7_9],
    [s_0_2, str[3..9]],
    [str[0..6], s_7_9]
  ]
end

answered Sep 8, 2019 at 10:20

iGian

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1 Comment

lacostenycoder Over a year ago

Yes, you are correct. My benchmark test shows about 25% faster .

lacostenycoder · Accepted Answer · 2019-09-08 07:19:16Z

2

What is your definition of "fast" ? Did you bench mark it?

require 'benchmark'
require 'SecureRandom'

arr = []

100_000.times { arr << SecureRandom.hex(5)}

def breakdown(str)
  [
    [str],
    [str[0..4], str[5..9]],
    [str[0..3], str[4..9]],
    [str[0..5], str[6..9]],
    [str[0..2], str[3..5], str[6..9]],
    [str[0..2], str[3..6], str[7..9]],
    [str[0..3], str[4..6], str[7..9]],
    [str[0..2], str[3..9]],
    [str[0..6], str[7..9]]
  ]
end

Benchmark.bm do |x|
  x.report { arr.each{|a| breakdown a} }
end

       user     system      total        real
a  0.337387   0.001583   0.338970 (  0.341292)

answered Sep 8, 2019 at 7:19

lacostenycoder

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