Remove leading and trailing zeroes

Question

Given a non-empty list/array containing only non-negative integers like this:

[0, 0, 0, 8, 1, 4, 3, 5, 6, 4, 1, 2, 0, 0, 0, 0]

Output the list with trailing and leading zeroes removed.

The output for this would be:

[8, 1, 4, 3, 5, 6, 4, 1, 2]

Some other test cases:

[0, 4, 1, 2, 0, 1, 2, 4, 0] > [4, 1, 2, 0, 1, 2, 4]
[0, 0, 0, 0, 0, 0] > nothing
[3, 4, 5, 0, 0] > [3, 4, 5]
[6] > [6]

Shortest code wins

Answer 1

Jelly, 2 bytes

Code:

t0

Explanation:

t   # Trim off...
 0  #  zero at both sides

Try it online!

Answer 2

JavaScript (ES6) 43

a=>(f=a=>a.reverse().filter(x=>a|=x))(f(a))

Less golfed

a=>{
  f=a=>a.reverse().filter(x=>a|=x) // reverse and remove leading 0
  // leverage js cast rules: operator | cast operands to integer
  // an array casted to integer is 0 unless the array is made of
  // a single integer value (that is ok for me in this case)
  return f(f(a)) // apply 2 times
}

Test

F=a=>(f=a=>a.reverse().filter(x=>a|=x))(f(a))

function test(){
  var l=(I.value.match(/\d+/g)||[]).map(x=>+x)
  O.textContent=F(l)
}

test()

#I { width:90%}

<input id=I oninput='test()' value='0 0 1 3 7 11 0 8 23 0 0 0'>
<pre id=O></pre>

Answer 3

CJam, 13 bytes

l~{_{}#>W%}2*

With the array inputted.

Longer version:

l~             Puts input on the stack and parse as array
  {       }    Code block
   _           Duplicate the first thing on the stack
    {}#        Finds the index of the first non-0 value in the array, puts it on the stack
       >       Slices the array from that index
        W%     Reverses the array
           2*  Does the code block twice in total

Answer 4

Pyth, 4 bytes

.sQ0

Demo:

llama@llama:~$ pyth -c .sQ0
[0, 0, 0, 1, 2, 0, 3, 4, 0, 0, 5, 0, 0, 0, 0]
[1, 2, 0, 3, 4, 0, 0, 5]

From Pyth's rev-doc.txt:

.s <seq> <any>
    Strip from A maximal prefix and suffix of A consisting of copies of B.

Answer 5

05AB1E, 4 bytes

Code:

0Û0Ü

Try it online!

Explanation:

0Û    # Trim off leading zeroes
  0Ü  # Trim off trailing zeroes

Uses CP-1252 encoding.

Answer 6

Retina, 12 bytes

^0 ?

)` 0$

The trailing linefeed is significant.

Thanks to @Martin Büttner and @FryAmTheEggman for saving a few bytes.

Try it online

Answer 7

R, 43 bytes

function(x)x[cummax(x)&rev(cummax(rev(x)))]

or as read/write STDIN/STDOUT

x=scan();cat(x[cummax(x)&rev(cummax(rev(x)))])

---

This finds the cumulative maximum from the beginning and the end (reversed) string. The & operator converts these two vectors to logical one of the same size as x, (zeroes will always converted to FALSE and everything else to TRUE), this way it makes it possible to subset from x according to the met conditions.

Answer 8

Haskell, 29 bytes

t=f.f;f=reverse.dropWhile(<1)

Answer 9

Mathematica 34 27 bytes

#//.{0,a___}|{a___,0}:>{a}&

This repeatedly applies replacement rules until such action fails to provide a new output. 7 bytes saved thanks to Alephalpha.

The first rule deletes a zero at the beginning; the second rule deletes a zero at the end of the array.

Answer 10

05AB1E, 4 bytes

0Û0Ü

Basically trimming leading then trailing zeroes of the input, given as an array.

Try it online !

Answer 11

Perl, 19 + 1 = 20 bytes

s/^(0 ?)+|( 0)+$//g

Requires -p flag:

$ perl -pE's/^(0 )+|( 0)+$//g' <<< '0 0 0 1 2 3 4 5 6 0 0 0'
1 2 3 4 5 6

Answer 12

Jelly, 10 bytes

Uo\U,o\PTị

This doesn't use the builtin.

Uo\U            Backward running logical OR
    ,           paired with
     o\         Forward running logical OR
       P        Product
        T       All indices of truthy elements
         ị      Index the input at those values.

Try it here.

Answer 13

MATL, 9 bytes

2:"PtYsg)

Try it online!

Explanation

2:"     % For loop (do the following twice)
  P     %   Flip array. Implicitly asks for input the first time
  t     %   Duplicate
  Ys    %   Cumulative sum
  g     %   Convert to logical index
  )     %   Apply index
        % Implicitly end for
        % Implicitly display stack contents

Answer 14

Perl, 38 bytes

$\.=$_}{$\=~s/^(0\n)*|(0\n)*\n$//gs

Run with perl -p, (3 bytes added for -p).

Accepts numbers on STDIN, one per line; emits numbers on STDOUT, one per line, as a well-behaved unix utility should.

Only treats numbers represented exactly by '0' as zeroes; it would be possible to support other representations with a few more bytes in the regex.

Longer version, still to be run with -p:

    # append entire line to output record separator
    $\.=$_
}{
    # replace leading and trailng zeroes in output record separator
    $\ =~ s/^(0\n)*|(0\n)*\n$//gs
    # output record separator will be implicitly printed

Expanded version, showing interactions with -p flag:

# implicit while loop added by -p
while (<>) {
    # append line to output record separator
    $\.=$_
}{ # escape the implicit while loop
    # replace leading and traling 
    $\=~s/^(0\n)*|(0\n)*\n$//gs
    # print by default prints $_ followed by
    # the output record separator $\ which contains our answer
    ;print # implicit print added by -p
} # implicit closing brace added by -p

Answer 15

Elixir, 77 bytes

import Enum
z=fn x->x==0 end
reverse(drop_while(reverse(drop_while(l,z)),z))

l is the array.

Edit:wah! copy/pasta fail. of course one has to import Enum, which raises the byte count by 12 (or use Enum.function_name, which will make it even longer).

Answer 16

Vitsy, 13 bytes

Vitsy is slowly getting better... (I'm coming for you Jelly. ಠ_ಠ)

1mr1m
D)[X1m]

This exits with the array on the stack. For readability, the TryItOnline! link that I have provided below the explanation will output a formatted list.

Explanation:

1mr1m
1m      Do the second line of code.
  r     Reverse the stack.
   1m   I'ma let you figure this one out. ;)

D)[X1m]
D       Duplicate the top item of the stack.
 )[   ] If the top item of the stack is zero, do the stuff in brackets.
   X    Remove the top item of the stack.
    1m  Execute the second line of code.

Note that this will throw a StackOverflowException for unreasonably large inputs.

TryItOnline!

Answer 17

R, 39 bytes

function(x)x[min(i<-which(x>0)):max(i)]

Four bytes shorter than David Arenburg's R answer. This implementation finds the first and last index in the array which is greater than zero, and returns everything in the array between those two indices.

Answer 18

Ruby, 49 44 bytes

->a{eval ?a+'.drop_while{|i|i<1}.reverse'*2}

Thanks to manatwork for chopping off 5 bytes with a completely different method!

This just drops the first element of the array while it's 0, reverses the array, repeats, and finally reverses the array to return it to the proper order.

Answer 19

Dyalog APL, 15 bytes

{⌽⍵↓⍨+/0=+\⍵}⍣2

               ⍣2     Apply this function twice:
{             }       Monadic function:
           +\⍵        Calculate the running sum.
       +/0=           Compare to zero and sum. Number of leading zeroes.
   ⍵↓⍨               Drop the first that many elements from the array.
 ⌽                   Reverse the result.

Try it here.

Answer 20

Vim 16 Keystrokes

i<input><esc>?[1-9]<enter>lD0d/<up><enter>

The input is to be typed by the user between i and esc, and does not count as a keystroke. This assumes that there will be at least one leading and one trailing zero. If that is not a valid assumption, we can use this slightly longer version: (18 Keystrokes)

i <input> <esc>?[1-9]<enter>lD0d/<up><enter>

Answer 21

ES6, 51 bytes

f=a=>a.map(x=>x?t=++i:f<i++||++f,f=i=0)&&a.slice(f,t)

t is set to the index after the last non-zero value, while f is incremented as long as only zeros have been seen so far.

Answer 22

Perl 6, 23 bytes

{.[.grep(?*):k.minmax]}
{.[minmax .grep(?*):k]}

Usage:

# replace the built-in trim subroutine
# with this one in the current lexical scope
my &trim = {.[.grep(?*):k.minmax]}

say trim [0, 0, 0, 8, 1, 4, 3, 5, 6, 4, 1, 2, 0, 0, 0, 0];
# (8 1 4 3 5 6 4 1 2)
say trim [0, 4, 1, 2, 0, 1, 2, 4, 0];
# (4 1 2 0 1 2 4)
say trim [0, 0, 0, 0, 0, 0];
# ()
say trim [3, 4, 5, 0, 0];
# (3 4 5)
say trim [6];
# (6)

Answer 23

JavaScript (ES6), 47 bytes

a=>a.join(a="").replace(/(^0+|0+$)/g,a).split(a)

Where a is the array.

Answer 24

Retina, 11 bytes

+`^0 ?| 0$
<empty>

Quite simple. Recursively replaces zeroes at beginning and end of line.

Try it online!

Answer 25

PHP, 56 54 52 bytes

Uses Windows-1252 encoding

String based solution

<?=preg_replace(~ÜÒ×ßÏÖÔƒ×ßÏÖÔÛÜ,"",join($argv,~ß));

Run like this:

echo '<?=preg_replace(~ÜÒ×ßÏÖÔƒ×ßÏÖÔÛÜ,"",join($argv,~ß));' | php -- 0 0 123 234 0 500 0 0 2>/dev/null;echo

If your terminal is set to UTF-8, this is the same:

echo '<?=preg_replace("#-( 0)+|( 0)+$#","",join($argv," "));' | php -- 0 0 123 234 0 500 0 0 2>/dev/null;echo

Tweaks

• Saved 2 bytes by negating strings and dropping string delimiters
• Saved 2 bytes by using short print tag

Answer 26

Python, 84 characters

def t(A):
 if set(A)<={0}:return[]
 for i in(0,-1):
  while A[i]==0:del A[i]
 return A

Answer 27

Python 2, 69 67 bytes

def f(a):
 for i in(0,-1):
  while a and a[i]==0:a.pop(i)
 return a

Answer 28

JavaScript (ES6), 34 bytes

a=>a.replace(/^(0 ?)*|( 0)*$/g,'')

Input and output are in the form of a space-delimited list, such as "0 4 1 2 0 1 2 4 0".

Answer 29

Javascript (ES6) 40 bytes

a=>/^(0,)*(.*?)(,0)*$/.exec(a.join())[2]

Answer 30

PowerShell, 49 bytes

($args[0]-join',').trim(',0').trim('0,')-split','

Takes input $args[0] and -joins them together with commas to form a string. We then use the .Trim() function called twice to remove first the trailing and then the leading zeros and commas. We then -split the string on commas back into an array.

---

Alternate version, without using conversion
PowerShell, 81 bytes

function f{param($a)$a=$a|%{if($_-or$b){$b=1;$_}};$a[$a.Count..0]}
f(f($args[0]))

Since PowerShell doesn't have a function to trim arrays, we define a new function f that will do half of this for us. The function takes $a as input, then loops through each item with a foreach loop |%{...}. Each iteration, we check a conditional for $_ -or $b. Since non-zero integers are truthy, but $null is falsey (and $b, being not previously defined, starts as $null), this will only evaluate to $true once we hit our first non-zero element in the array. We then set $b=1 and add the current value $_ onto the pipeline. That will then continue through to the end of the input array, with zeros in the middle and the end getting added onto the output, since we've set $b truthy.

We encapsulate and store the results of the loop all back into $a. Then, we index $a in reverse order (i.e., reversing the array), which is left on the pipeline and thus is the function's return value.

We call the function twice on the $args[0] input to the program in order to "trim" from the front, then the front again (which is the back, since we reversed). The order is preserved since we're reversing twice.

This version plays a little loose with the rules for an input array of all zeros, but since ignoring STDERR is accepted practice, the program will spit out two (verbose) Cannot index into a null array errors to _{(PowerShell's equivalent of)} STDERR and then output nothing.

Answer 31

Mathematica, 33 bytes

#/.{Longest[0...],x__,0...}->{x}&

Answer 32

jq, 48 characters

. as$a|map(.>0)|indices(1>0)|$a[min:(max//-1)+1]

Sample run:

(Command line option -c only used in this sample for readability to avoid pretty printing the result.)

bash-4.3$ jq -c '. as$a|map(.>0)|indices(1>0)|$a[min:(max//-1)+1]' <<< '[0, 4, 1, 2, 0, 1, 2, 4, 0]'
[4,1,2,0,1,2,4]

bash-4.3$ jq -c '. as$a|map(.>0)|indices(1>0)|$a[min:(max//-1)+1]' <<< '[0, 0, 0, 0, 0, 0]'
[]

On-line test:

• [0, 4, 1, 2, 0, 1, 2, 4, 0]
• [0, 0, 0, 0, 0, 0]

Answer 33

Groovy, 43 characters

{x={it.dropWhile{it<1}.reverse()};x(x(it))}

Sample run:

groovy:000> ({x={it.dropWhile{it<1}.reverse()};x(x(it))})([0, 4, 1, 2, 0, 1, 2, 4, 0])
===> [4, 1, 2, 0, 1, 2, 4]

groovy:000> ({x={it.dropWhile{it<1}.reverse()};x(x(it))})([0, 0, 0, 0, 0, 0])
===> []

Answer 34

sed, 24 bytes

#!/bin/sed -f
:
s/ 0$//
s/^0\b \?//
t

Input as space-separated words on stdin.

It cost me five bytes (\b \?) to deal with the special case of all zeros.

Test results

$ ./71877.sed <<EOF
0 0 0 8 1 4 3 5 6 4 1 2 0 0 0 0
0 4 1 2 0 1 2 4 0
0 0 0 0 0 0
3 4 5 0 0
6
EOF
8 1 4 3 5 6 4 1 2
4 1 2 0 1 2 4

3 4 5
6

Answer 35

C#, 134 bytes

using System.Linq;n=>string.Join(" ",n).Trim('0',' ').Split(new[]{' '},StringSplitOptions.RemoveEmptyEntries).Select(s=>int.Parse(s));

If I can return a comma separated string of the return values:

C#, 36 bytes

n=>string.Join(",",n).Trim('0',',');

Answer 36

PHP, 61 bytes

<?=preg_replace("^[^_]*_(0_)*(.*)(_0)*$","$2",join(_,$argv));

regexp using the underscore as delimiter.

Answer 37

PHP, 41 Bytes

<?="[".trim(join(",",$_GET[a]),",0")."]";

If the input as array could be write as ?a=0&b=0 and so on it can be reduce to 38 Bytes

<?="[".trim(join(",",$_GET),",0")."]";

The longer way working with Regex 65 Bytes

<?="[".preg_replace("#^(0,)*|(,0)*$#","",join(",",$_GET[a]))."]";

Answer 38

///, 20 bytes

/[0 /[// 0]/]//[0]//

Try it online!

Input as list of integers separated by spaces and surrounded by square brackets ([0 1 2 3 4 5 0]).

Answer 39

PHP, 30 bytes

<?=trim(join(' ',$argv),' 0');

Needs to be saved in a file called '0' (or any number of 0s). Works with all test cases (which are <10 at time of submission) but if a test case with a final non 0 integer of 10 (or any other integer with a 0 units digit) gets added then it will no longer be valid.

use like:

php 0 0 4 1 2 0 1 2 4 0

Where the first 0 is the file name and the rest is the input

A bunch of answers got added between me loading the challenge and submitting this. I'd delete it but I never finished the account sign up, would a mod do so please?

Answer 40

Pari/GP, 27 bytes

p->Vecrev(polrecip(Pol(p)))

When a list is converted to a polynomial, the leading zeros are removed. Then we can take the reciprocal polynomial, and convert it back to a list, and the trailing zeros are removed.

Try it online!

Answer 41

Racket 73 bytes

(λ(l)(define(g k)(if(= 0(car k))(g(cdr k))k))(reverse(g(reverse(g l)))))

Ungolfed:

(define f
  (λ(l)
    (define (g k)                     ; fn to remove leading zeros; 
        (if(= 0 (first k))
           (g (rest k))
           k))
    (reverse (g (reverse (g l))))))

Last line removes leading 0s in original and reversed list. List is re-reversed to get original order.

Testing with different combinations:

(f '(0 0   2 5 0 6 8 9   0 0))
(f '(0 0 0 2 5 0 6 8 9   0 0 0))

(f '(0 0 0 2 5 0 6 8 9   0 0))
(f '(0 0   2 5 0 6 8 9   0 0 0))

(f '(0 0   2 5 0 6 8 9))
(f '(0 0 0 2 5 0 6 8 9))

(f '(2 5 0 6 8 9   0 0))
(f '(2 5 0 6 8 9   0 0 0))

(f '(2 5 0 6 8 9))

Output:

'(2 5 0 6 8 9)
'(2 5 0 6 8 9)
'(2 5 0 6 8 9)
'(2 5 0 6 8 9)
'(2 5 0 6 8 9)
'(2 5 0 6 8 9)
'(2 5 0 6 8 9)
'(2 5 0 6 8 9)
'(2 5 0 6 8 9)

Answer 42

PHP, 144 126 chars

• -18 chars thanks to @manatwork

It's a bit longer than the other PHP answers because it's array-based.

function e($a){foreach($a as$i=>$v){if($v)break;unset($a[$i]);}return array_reverse($a);}print_r(e(e(explode(",",$argv[1]))));

Call like this: php remove0.php 0,4,2,1,0,1,2,4,0

Example return:

Array
(
    [0] => 4
    [1] => 2
    [2] => 1
    [3] => 0
    [4] => 1
    [5] => 2
    [6] => 4
)

Answer 43

Python 3, 48 55 29 26 bytes

print(input().strip('0 '))

Input and output is taken as space-separated numbers, eg:

0 0 0 1 3 1 4 0 1 3 6 4 5 19 3 1 4 0

Alternatively, a 29-byte Python 2 solution:

print raw_input().strip('0 ')