Rebuild a rectangular array from a corner

Question

I once had a beautiful rectangular array. It was very symmetrical, but unfortunately it has fallen apart and now I only have the top left corner. Your task will be to rebuild the original array.

Your program will receive a 2 dimensional array of integers. For ease of parsing, you may assume they are all between 1 and 9. Your task is to reverse the array's columns, its rows, and both, stitch together the resulting corners, and return the resulting array.

You can assume the array dimensions will be at least 1x1.

Test cases:

Input:
1 2 3
4 5 6

Output:
1 2 3 3 2 1
4 5 6 6 5 4
4 5 6 6 5 4
1 2 3 3 2 1

---

Input:
1

Output:
1 1
1 1

---

Input:
9
9
9

Output:
9 9
9 9
9 9
9 9
9 9
9 9

This is code-golf, fewest bytes wins!

Answer 1

Proton, 29 bytes

a=>[b+b[by-1]for b:a+a[by-1]]

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There are a few other interesting approaches though:

Proton, 29 bytes

a=>map(g,(g=x=>x+x[by-1])(a))

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You can define the mirror sub-function g in-line, because Proton. It's not shorter though.

Proton, 36 bytes

(a=>[x[0]for x:zip(*(a+a[by-1]))])*2

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This should be (a=>zip(*(a+a[by-1])))*2 which is 24 bytes, but the zip function is completely broken. Basically, you mirror it and zip, and then do that twice (you can multiply a function by a positive integer to apply the function multiple times).

Answer 2

Canvas, 1 byte

╬

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Outputs as a multiline string

Answer 3

Haskell, 25 24 bytes

r=(++)<*>reverse
r.map r

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Answer 4

Python 3, 38 bytes

lambda a:[b+b[::-1]for b in a+a[::-1]]

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Takes a list of lists and returns a list of lists.

Explanation:

lambda a:                              # anonymous lambda function
                   for b in a+a[::-1]  # for each row in the array and the upside-down array
          b+b[::-1]                    # the row with its reverse appended
         [                           ] # return in a list

Answer 5

Husk,  7  6 bytes

Coincidentally, Erik had posted the exact same code in the Husk chatroom about a minute before I posted this.

‼oTS+↔

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Pervious version, 7 bytes:

mS+↔S+↔

Answer 6

05AB1E, 2 bytes

∞∊

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---

   # Input:Array of String | ['12','34']
---#-----------------------+------------------------------------------
∞  # Mirror horizontally.  | [12,34]       -> [1221,3443]
 ∊ # Mirror vertically.    | [1221,3443]   -> [1221\n3443\n3443\n1221]

---

Credit for Mr. Xcoder pointing out that arrays of string may count as 2D arrays and Pavel for confirming it.

Answer 7

Retina, 13 bytes

\%`$
$^$`
Vs`

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Explanation

\%`$
$^$`

On each line (%), match the end of the line ($), and insert the reverse ($^) of the entire line ($`) and print the result with a trailing linefeed (\). This does the reflection along the vertical axis and prints the first half of the output.

Vs`

This just reverses the entire string, which is equivalent to a 180° degree rotation, or in our case (due to the horizontal symmetry) a reflection along the horizontal axis. This way this works is that V's (reverse) default regex is (?m:^.*$), which normally matches each line of the string. However, we activate the singleline option s, which makes . match linefeeds as well and therefore this default regex actually matches the entire string.

The result of this is printed automatically at the end of the program, giving us the second half of the output.

Answer 8

Jelly, 5 bytes

m€0m0

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Answer 9

MATL, 5 bytes

,tPv!

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Explanation:

(implicit input)
,               # do twice:
 t              # dup top of stack
 P              # flip vertically
 v              # vertically concatenate
 !              # transpose
(implicit output)

Answer 10

Octave,  33  29 bytes

Thanks to @Giuseppe for golfing four bytes!

@(A)[B=[A;flip(A)] fliplr(B)]

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Answer 11

JavaScript (Node.js), 62 55 49 46 bytes

A=>(j=x=>[...x,...[...x].reverse()])(A).map(j)

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Because Array.prototype.reverse() reverses the array in place, I have to make a shallow copy somewhere first. A=>(j=x=>[...x,...x.reverse()])(A).map(j) does not work.

Answer 12

J, 12 bytes

(,|.)@,.|."1

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Explanation

         |."1 - reverse each row
       ,.     - and stitch them to the input
 (   )@       - and 
  ,|.         - append the rows in reversed order        

Answer 13

awk, 88 bytes

{s="";for(i=NF;i>0;i--)s=" "$i s" "$i;a[FNR]=s;print s}END{for(i=NR;i>0;i--)print a[i]}

Answer 14

Triangularity, 31 bytes

...)...
..IEM..
.DRs+}.
DRs+...

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Explanation

Removing the characters that make up for the padding, here is what the program does:

)IEMDRs+}DRs+ – Full program. Takes a matrix as a 2D list from STDIN.
)             – Push a 0 onto the stack.
 I            – Take the input at that index.
  E           – Evaluate it.
   M    }     – For each row...
    DR        – Duplicate and replace the second copy by its reverse.
      s+      – Swap and append.
         DR   – Duplicate the result and replace the second copy by its reverse.
           s+ – Swap and append.

Answer 15

R, 57 bytes

function(m)rbind(N<-cbind(m,m[,ncol(m):1]),N[nrow(N):1,])

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Answer 16

APL+WIN, 11 bytes

Prompts for a 2d array of integers.

m⍪⊖m←m,⌽m←⎕

Answer 17

Stax, 5 bytes

:mm:m

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:m means mirror, which is input.concat(reverse(input)). m, in this context means output each line after applying...

So, mirror the array of rows, and then mirror each row and output.

Answer 18

SNOBOL4 (CSNOBOL4), 119 113 bytes

	T =TABLE()
I	X =X + 1
	I =INPUT	:F(D)
	OUTPUT =T<X> =I REVERSE(I)	:(I)
D	X =X - 1
	OUTPUT =GT(X) T<X>	:S(D)
END	

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Takes input as strings on STDIN, without spaces. This only works because the digits are 1-9 and would fail otherwise.

Answer 19

Add++, 30 bytes

D,f,@,bU€{r}B]{r}
D,r,@,dbR+

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The footer simply transforms the nested array into the format in the question. Defines a function f, which expects a matrix (nested array) as an argument.

Answer 20

Japt, 6 bytes

mê1 ê1

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---

Explanation

           :Implicit input of 2D array
m          :Map
 ê1        :  Mirror sub array
    ê1     :Mirror main array

Answer 21

Charcoal, 5 bytes

θ‖Ｃ→↓

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Thanks to ASCII-only for a better input format.

Answer 22

Mathematica, 29 bytes

(g=#~Join~Reverse@#&)@*Map[g]

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Answer 23

SOGL V0.12, 2 bytes

-1 byte thanks to dzaima.

╬ø

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Answer 24

APL (Dyalog Classic), 7 bytes

⍪∘⊖⍨⊢,⌽

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Answer 25

Ruby, 35 bytes

->a{r=->b{b+b.reverse}
r[a].map &r}

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A lambda accepting a 2D array and returning a 2D array. It's straightforward, but here's the ungolfed version anyway:

->a{
  r=->b{ b+b.reverse } # r is a lambda that returns the argument and its reverse
  r[a].map &r          # Add the array's reverse, then add each row's reverse
}

Answer 26

C (gcc), 114 111 bytes

• Saved three bytes thanks to Kevin Cruijssen; inverting the loops.

j,i;f(A,w,h)int*A;{for(i=h+h;i-->0;puts(""))for(j=w+w;j-->0;)printf("%d,",A[(i<h?i:h+h+~i)*w+(j<w?j:w+w+~j)]);}

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C (gcc), 109 bytes (abusing ease of parsing)

• Thanks to Kevin Cruijssen for suggesting to only allow one-digit input integers; saved two bytes.

j,i;f(A,w,h)int*A;{for(i=h+h;i-->0;puts(""))for(j=w+w;j-->0;)putchar(A[(i<h?i:h+h+~i)*w+(j<w?j:w+w+~j)]+48);}

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Answer 27

Java 8, 140 131 bytes

m->{String r="";for(int a=m.length,b=m[0].length,i=a+a,j;i-->0;r+="\n")for(j=b+b;j-->0;)r+=m[i<a?i:a+a+~i][j<b?j:b+b+~j];return r;}

Explanation:

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m->{                      // Method with integer-matrix parameter and String return-type
  String r="";            //  Result-String, starting empty
  for(int a=m.length,     //  Amount of rows of the input-matrix
          b=m[0].length,  //  Amount of columns of the input-matrix
          i=a+a,j;        //  Index integers
      i-->0;              //  Loop over double the rows
      r+="\n")            //    After every iteration: append a new-line to the result
     for(j=b+b;j-->0;)    //   Inner loop over double the columns
       r+=                //    Append the result with:
          m[i<a?          //     If `i` is smaller than the amount of rows
             i            //      Use `i` as index in the input-matrix
            :             //     Else:
             a+a+~i]      //      Use `a+a+i-1` as index instead
           [j<b?          //     If `j` is smaller than the amount of columns
             j            //      Use `j` as index in the input-matrix
            :             //     Else:
             b+b+~j];     //      Use `b+b+j-1` as index instead
  return r;}              //  Return the result-String

Answer 28

J, 11 bytes

Anonymous tacit prefix function.

|:@(,|.)^:2

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|: transpose

@(…) the result of:

 , the argument followed by

 |. its reverse

^:2 and all this done twice

Answer 29

V, 12 bytes

yGæGPÎy$æ_|P

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Explanation:

yG              " Yank every line
  æG            " Reverse the order of the lines
    P           " Paste what we yanked
     Î          " On every line:
      y$        "   Yank the whole line
        æ_      "   Reverse the whole line
          |     "   Move to the beginning of the line
           P    "   Paste what we yanked

Answer 30

Julia 0.6, 55 49 bytes

~i=i:-1:1
!x=[x x[:,~end];x[~end,:] x[~end,~end]]

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~(i) is a function to create slice from i down to 1.
So ~end gives the slice end:-1:1

!(x) is the function to do the rebuilding of the array.

Answer 31

Python 3, 49 bytes

def f(a):o=[i+i[::-1]for i in a];return o+o[::-1]

Where a is the input array. This function will return a 2D array.

Answer 32

Clojure, 56 bytes

(fn[i](map #(concat %(reverse %))(concat i(reverse i))))

Creates an anonymous function which takes the two dimensional list and returns the fixed rectangle as two dimensional list.

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Answer 33

Perl 5 -lp -Mfeature=say, 36 bytes

unshift@l,$_.=reverse;END{say for@l}

Deparsed:

BEGIN { $/ = "\n"; $\ = "\n"; }
use feature 'say';
LINE: while (defined($_ = readline ARGV)) {
    chomp $_;
    unshift @l, $_ .= reverse;
    sub END {
        say $_ foreach (@l);
    }
}
continue {
    die "-p destination: $!\n" unless print $_;
}

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