16
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Given a string, you've to split it into groups of three characters (by padding _ at the end).

Related, but still it's different.


Sample I/O:

  • 'abcde' -> 'abc', 'de_'

  • '1234' -> '123', '4__'

  • '' -> [] or falsey value

  • 'Three spree!' -> 'Thr', 'ee ', 'spr', 'ee!'

  • 6 MB string

This is a , so fewest bytes will win!

Edit: Finally, output is unrestricted.

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  • 10
    \$\begingroup\$ Why special case the empty string? May we choose which character to use for the padding? \$\endgroup\$ – Shaggy May 19 at 14:49
  • 12
    \$\begingroup\$ So the task is actually: Given a string, return a falsey value if it is empty, otherwise split it into groups of three, padding with underscores if necessary? Seems like an odd pair-up of two unrelated tasks (checking string length and splitting). \$\endgroup\$ – Adám May 19 at 15:27
  • 14
    \$\begingroup\$ Things to avoid: Exceptional edge cases. In this case, an empty string should returnan empty array or equivalent, not a falsey value \$\endgroup\$ – Jo King May 19 at 22:05
  • 6
    \$\begingroup\$ Lots of statically-typed languages cannot return more than one type from a function \$\endgroup\$ – Embodiment of Ignorance May 19 at 23:30
  • 4
    \$\begingroup\$ @manassehkatz Yes, but only in those languages. In some languages it makes solutions far more complicated, or even impossible (e.g statically typed languages). \$\endgroup\$ – Jo King May 20 at 22:01

37 Answers 37

9
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05AB1E, 9 8 bytes

…___«3ô¨

Try it online! or as a Test Suite

Explanation

…___«      # append "___" to input
     3ô    # split into groups of 3
       ¨   # discard the last group
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8
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Python 3, 58 47 34 bytes

I'm sure someone else can do better Someone else did better. Thanks Jo King for -11 -24 bytes!

Output is unrestricted, welcome to tuple hell. Returns empty list (falsy) on empty input

lambda x:[*zip(*[iter(x+"__")]*3)]

TIO

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6
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JavaScript, 25 bytes

s=>`${s}__`.match(/.../g)

Try it

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5
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Perl 5, 16 15 bytes

"@_\__"=~/.../g

Try it online!

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  • 1
    \$\begingroup\$ 15 with "@_\__"=~/.../g. There were other 16s: (pop.__)=~/.../g or map/.../g,pop.__. \$\endgroup\$ – Grimmy May 20 at 11:50
  • 1
    \$\begingroup\$ Thx to @Grimy for the tip on \. It shaved off 1 byte and I learned something new. \$\endgroup\$ – Kjetil S. May 20 at 13:30
4
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APL+WIN 36 24 22 bytes

12 bytes saved as a result of output now being de-restricted and using the code in @Adám's first comment modified to work in APL+WIN and a further 2 with his second comment. Thanks.

(⌈(↑⍴s)÷3)3⍴(s←⎕),'__'

Prompts for input of the string and outputs the result as a nx3 array

Try it online! Courtesy of Dyalog Classic

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  • \$\begingroup\$ @Adám. Throws a domain error in APL+WIN at the right most ⍴ \$\endgroup\$ – Graham May 19 at 13:45
  • \$\begingroup\$ Fails on '', no? I think OP (for some strange reason) requires the result to be 0 (with any rank). \$\endgroup\$ – Adám May 19 at 15:47
  • 1
    \$\begingroup\$ @Adám It produces a 0 x 3 array. The OP now appears to want "falsey" for a null input. With the spec keeping on changing I am going to bow out at this point and leave my answer as its stands! Thanks for your improvements. \$\endgroup\$ – Graham May 19 at 16:12
4
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JavaScript, 51 50 48 27 25

b=>(b+"__").match(/.../g)

Try it online!

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  • \$\begingroup\$ Welcome to PPCG! :) But ... codegolf.stackexchange.com/a/185808/58974 \$\endgroup\$ – Shaggy May 24 at 16:51
  • \$\begingroup\$ @Shaggy I didn't even see that ¯\_(ツ)_/¯ \$\endgroup\$ – VFDan May 24 at 17:21
  • \$\begingroup\$ No worries, it happens. \$\endgroup\$ – Shaggy May 24 at 17:24
3
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Perl 6, 19 bytes

{$_~"__"~~m:g/.../}

Try it online!

Pads the string by two underscores then splits the string into chunks of three characters. Returns as an array of Match objects.

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3
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Japt, 8 bytes

+1 byte to special case the empty string. Can save 2 if we can choose our padding character.

©ò3 ú'_3

Try it

©ò3 ú'_3     :Implicit input of string
©            :Logical AND with
 ò3          :Split into chunks of 3
    ú'_3     :Right pad each with "_" to length 3
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2
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Stax, 7 bytes

é☻εgP▀╪

Run and debug it

For an empty string input, the result is an empty array, which is a falsey value in stax.

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2
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CJam, 11 bytes

q'_3*+3/);p

Try it online!

For empty input this gives an empty string, which is falsy.

How it works

q     e# Read input as a string
'_    e# Push char '_'
3*    e# String formed by that char repeated 3 times
+     e# Concatenate to input string
3/    e# Split in groups of 3, the last of which may be shorter. Gives array of strings
);    e# Detach last string from the array and delete it
p     e# Print string representation of the array
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2
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Retina 0.8.2, 10 bytes

$
__
!`...

Try it online! Link includes test cases. Explanation:

$
__

Append two _s, in case the last group needs to be padded.

!`...

Match as many groups of three as possible, outputting the matches themselves rather than the count. (In Retina 1 this would be L instead of !.)

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2
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C (gcc), 67 bytes

i;f(char*_){for(;*_;puts(""))for(i=3;i--;)putchar(*_?*_++:95);_=0;}

Try it online!

Always returns a falsey value (0).

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  • 1
    \$\begingroup\$ Do you even need to return anything? \$\endgroup\$ – ceilingcat May 20 at 14:11
  • \$\begingroup\$ 63 bytes \$\endgroup\$ – Johan du Toit May 21 at 10:28
2
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Wolfram Language (Mathematica), 28 21 bytes

-7: No longer requires falsy (False) value on empty input

Partition[#,3,1,1,_]&

Try it online!

Takes a list of characters as input. Returns a list of 3-tuples of characters padded with Blanks (_).


34 27 bytes

StringPartition[#<>"__",3]&

Try it online!

String input, list of strings output

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1
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Jelly, 9 bytes

s3o€“___”

A monadic Link accepting a list of characters which yields a list of lists of characters (an empty input yields empty output).

Try it online!

How?

s3o€“___” - Link: list of characters
s3        - split into chunks of three
   €      - for each chunk:
  o       -   OR (vectorises):
    “___” -     list of characters = ['_', '_', '_']

Notes:
The is only necessary to handle the edge case of an empty input.
A full program can drop a trailing , but here we can't do that as the printing behaviour of a full program smashes everything together.


Equivalent 9:

o3ÐƤ“___”

Try it


Alternative 9:

;“___”s3Ṗ

Try it

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1
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J, 16 bytes

[:}:_3]\'___',~]

Try it online!

K (oK), 19 17 bytes

-2 bytes thanks to ngn!

{-1_0N 3#x,"___"}

Try it online!

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  • 1
    \$\begingroup\$ k: (0N;3) -> 0N 3 \$\endgroup\$ – ngn May 20 at 7:21
  • \$\begingroup\$ @ngn Thank you! \$\endgroup\$ – Galen Ivanov May 20 at 7:28
1
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Java 10, 116 113 bytes

s->{s+="__";int l=s.length()/3,i=l;var r=new String[l];for(;i-->0;)r[i]=s.substring(i*3,i*3+3);return l<1?0>1:r;}

Try it online.

Or 104 101 bytes if an empty array instead of false is allowed as output..

s->{s+="__";int l=s.length()/3;var r=new String[l];for(;l-->0;)r[l]=s.substring(l*3,l*3+3);return r;}

Try it online.

Explanation:

s->{                             // Method with String as both parameter and return-type
  s+="__";                       //  Append two "_" to the input-String
  int l=s.length()/3;            //  Get the length, integer-divided by 3
  var r=new String[l];           //  Create a string-array with that many parts
  for(;l-->0;)                   //  Loop `l` in the range (l, 0]:
    r[l]=                        //   Set the `l`'th value of the array to:
         s.substring(l*3,l*3+3); //   Get the substring of size 3 from index `l*3` from `s`
  return r;}                     //  Return the array
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  • \$\begingroup\$ An empty array is now allowed \$\endgroup\$ – Benjamin Urquhart May 26 at 3:57
1
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Ruby, 73 42 bytes

a=gets
a.length!=0?a.scan(/.{1,3}/).map{|s|(s+'_'*3)[0,3]}:'falsey value'

Edit: As falsey value looks like it's not required:

gets.scan(/.{1,3}/).map{|s|(s+'_'*3)[0,3]}
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  • 1
    \$\begingroup\$ The maximum padding is of 2 characters, so '_'*2 would be enough, for which a literal '__' is shorter. But if you add the padding in advance then simply not match the pieces shorter than 3 characters, is shorter: puts"#{gets}__".scan /.../. (Note that without the explicit printing that is considered irb not ruby.) \$\endgroup\$ – manatwork May 20 at 15:06
1
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C# (Visual C# Interactive Compiler), 74 bytes

Just append two underscores '_' at the end of the input to make sure they get printed if the length of the input isn't a factor of 3.

s=>Enumerable.Range(0,(s.Length+2)/3).Select(i=>(s+"__").Substring(i*3,3))

Try it online!

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  • \$\begingroup\$ 67 \$\endgroup\$ – dana May 22 at 5:20
  • \$\begingroup\$ 57 \$\endgroup\$ – someone May 25 at 1:22
1
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Kotlin, 34 bytes

{"${it}__".chunked(3).dropLast(1)}

Try it online!

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  • \$\begingroup\$ this does not work, try {"${it}___".chunked(3).dropLast(1)} \$\endgroup\$ – pme May 21 at 6:45
1
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C (gcc), 55 bytes

i;f(char*s){for(;i%4|*s;)putchar(++i%4?*s?*s++:95:10);}

Try it online!

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  • \$\begingroup\$ Using 9(\t) instead of 10(\n) should be fine, but that's not main point \$\endgroup\$ – l4m2 May 20 at 15:23
1
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C (clang), 128 126 94 67 bytes

67 bytes thanks to @ceilingcat

f(char*k){for(;*k;k++)printf("%c%c%c\n",*k,*++k?*k:95,*++k?*k:95);}

Try it online!

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1
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Bash, 90 bytes

This uses Bash features rather than a combination of more traditional Bourne shell plus *nix commands (which one version I created ended up at 205 bytes). I cheated by using the dodge of adding two _ characters to the string.

c=;read a;a=${a}__;while (($(echo ${#a})>2));do b=${a:0:3};c=$c\ $b;a=${a#$b};done;echo $c

Try it online!

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1
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PowerShell, 58 35 bytes

$args-split'(...)'-ne''|% *ht 3 '_'

-23 bytes thanks to mazzy.

Try it online!

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  • \$\begingroup\$ Nice. 1) You can count a code that can be extracted into a ps1-file and executed. 2) See shortcuts. 3) Try to golf more \$\endgroup\$ – mazzy May 25 at 5:18
1
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GNU sed, 27 bytes

s:$:__:
s:...:& :g
s: _*$::

Try it online!

It gets a bit tricky regarding the empty string input, since sed has no meaning of a falsy value. So to deal with this, I provide you with two possible interpretations of the rules to validate my submission:


A. You essentially provide nothing as input, not even a trailing newline (as it is the case with all the examples, including that 6 Mb file).

Usage:

echo -n ""|sed -f script

Output: nothing is printed, because sed doesn't even run the script without input.


B. One could consider as falsy value for sed to be an unique string, i.e., returned only when the input is an empty string.

Usage:

echo ""|sed -f script

Output:

__

I prefer the first interpretation so much more, as I believe it to be the closest to the intended rule, but the last one helps if you run the script using that TIO link.

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0
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JavaScript (Babel Node), 45 bytes

_=>_.match(/.{1,3}/g).map(a=>a.padEnd(3,`_`))

Try it online!

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  • \$\begingroup\$ 44 \$\endgroup\$ – Shaggy May 19 at 15:13
  • \$\begingroup\$ Doesn't work for me \$\endgroup\$ – VFDan May 22 at 21:55
0
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Jelly, 10 bytes

s3;€⁾__ḣ€3

Try it online!

It feels like an 8 or 9 should be possible, but haven’t found one yet.

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0
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Attache, 34 23 bytes

PadRight&"_"&3=>@Chop&3

Try it online!

Explanation (outdated)

{On[#_-1,PadRight&"_"&3,_]}@Chop&3
                           @Chop&3    chop the input string into groups of 3s
{On[#_-1               ,_]}           on the last group
        ,PadRight                         pad it
                     &3                   to length three
                 &"_"                     with underscores
\$\endgroup\$
  • \$\begingroup\$ Would you save anything by padding all the elements instead of just the last one? \$\endgroup\$ – Shaggy May 19 at 20:18
  • \$\begingroup\$ @Shaggy Good point! I’ll look into it \$\endgroup\$ – Conor O'Brien May 19 at 20:19
0
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Charcoal, 10 bytes

E⪪S³…⁺ι__³

Try it online! Link is to verbose version of code. Explanation:

  S         Input string
 ⪪ ³        Split into groups of up to 3 characters
E           Map over each group
      ι     Current group
     ⁺      Concatenated with
       __   Literal `__`
    …    ³  Moulded to length 3
            Each group implicitly printed on its own line
\$\endgroup\$
0
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Scala, 31 bytes

(s+"___").grouped(3).toSeq.init

Try it online!

Explanation

(s+"___")       // add "___"
  .grouped(3)   // make groups of 3
  .toSeq        // change to Seq
  .init         // take all but last
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0
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Befunge-93, 30 29 bytes

~:1+%,~:1+!"`"*+,~:1+!"`"*+,,

Try it online!

Outputs nothing for an empty input, otherwise outputs strings of length 3 separated by NUL characters.

Explanation:

~                               Push character of input to stack
 :1+                            Duplicate input and add 1
    %                           Modulo top 2 values of stack and push result
                                If input was -1 (end of stream), calculate -1%0 -> halt
                                Otherwise calculate input%(input+1) -> input
     ,                          Pop and output character
      ~                         Push character of input to stack
       :1+!                     Duplicate input, add 1 and perform logical NOT
           "`"*                 Multiply by 96 (ASCII code for '`')
                                This returns 96 or 0 depending on the result of the NOT
               +                Add the top 2 values from the stack and push the result
                                If the input was -1 (end of stream), pushes -1+96=95, or the ASCII code for '_'
                                Otherwise pushes input+0
                ,               Pop and output character
                 ~:1+!"`"*+,    Same block again to handle the third character
                            ,   Output a NUL character (stack is empty, so popping from stack just returns 0)

The instruction pointer wraps around at the end, looping the entire line.
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