35
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The task

This challenge is very simple. Your input is a rectangular 2D array of integers, sized at least 1×1. It can be taken in any reasonable format. Your output shall be the input array, but with all entries not on the first or last row or column set to 0. It must be in the same format as the input.

For example, if the input array is

67  4 -8  5 13
 9 13 42  4 -7
 1  1  3 -9 29
16 99  8 77  0

then the correct output is

67  4 -8  5 13
 9  0  0  0 -7
 1  0  0  0 29
16 99  8 77  0

Rules and scoring

You can write a full program or a function, and functions are allowed to modify the input in place instead of returning it. The lowest byte count wins, and standard loopholes are disallowed.

Test cases

These are formatted as nested lists to make copy-pasting easier.

[[3]] -> [[3]]
[[7,2,8]] -> [[7,2,8]]
[[3],[5],[12],[-6]] -> [[3],[5],[12],[-6]]
[[99,98,97],[88,87,86]] -> [[99,98,97],[88,87,86]]
[[6,7],[8,9],[10,11]] -> [[6,7],[8,9],[10,11]]
[[-1,-2,-3],[1,2,3],[5,5,5]] -> [[-1,-2,-3],[1,0,3],[5,5,5]]
[[67,4,-8,5,13],[9,13,42,4,-7],[1,1,3,-9,29],[16,99,8,77,0]] -> [[67,4,-8,5,13],[9,0,0,0,-7],[1,0,0,0,29],[16,99,8,77,0]]
[[0,1,0,1,0],[1,0,1,0,1],[0,1,0,1,0],[1,0,1,0,1],[0,1,0,1,0]] -> [[0,1,0,1,0],[1,0,0,0,1],[0,0,0,0,0],[1,0,0,0,1],[0,1,0,1,0]]

Leaderboard

Here is a Stack Snippet to generate both a regular leaderboard and an overview of winners by language. To make sure that your answer shows up, please start your answer with a headline, using the following Markdown template:

## Language Name, N bytes

If you want to include multiple numbers (e.g. because you've improved your score or you want to list interpreter flags separately), make sure that the actual score is the last number in the header:

## Perl, <s>50</s> 43 + 2 (-p flag) = 45 bytes

You can also make the language name a link which will then show up in the leaderboard snippet:

## [><>](http://esolangs.org/wiki/Fish), 121 bytes

var QUESTION_ID=71591,OVERRIDE_USER=32014;function answersUrl(e){return"https://api.stackexchange.com/2.2/questions/"+QUESTION_ID+"/answers?page="+e+"&pagesize=100&order=desc&sort=creation&site=codegolf&filter="+ANSWER_FILTER}function commentUrl(e,s){return"https://api.stackexchange.com/2.2/answers/"+s.join(";")+"/comments?page="+e+"&pagesize=100&order=desc&sort=creation&site=codegolf&filter="+COMMENT_FILTER}function getAnswers(){jQuery.ajax({url:answersUrl(answer_page++),method:"get",dataType:"jsonp",crossDomain:!0,success:function(e){answers.push.apply(answers,e.items),answers_hash=[],answer_ids=[],e.items.forEach(function(e){e.comments=[];var s=+e.share_link.match(/\d+/);answer_ids.push(s),answers_hash[s]=e}),e.has_more||(more_answers=!1),comment_page=1,getComments()}})}function getComments(){jQuery.ajax({url:commentUrl(comment_page++,answer_ids),method:"get",dataType:"jsonp",crossDomain:!0,success:function(e){e.items.forEach(function(e){e.owner.user_id===OVERRIDE_USER&&answers_hash[e.post_id].comments.push(e)}),e.has_more?getComments():more_answers?getAnswers():process()}})}function getAuthorName(e){return e.owner.display_name}function process(){var e=[];answers.forEach(function(s){var r=s.body;s.comments.forEach(function(e){OVERRIDE_REG.test(e.body)&&(r="<h1>"+e.body.replace(OVERRIDE_REG,"")+"</h1>")});var a=r.match(SCORE_REG);a&&e.push({user:getAuthorName(s),size:+a[2],language:a[1],link:s.share_link})}),e.sort(function(e,s){var r=e.size,a=s.size;return r-a});var s={},r=1,a=null,n=1;e.forEach(function(e){e.size!=a&&(n=r),a=e.size,++r;var t=jQuery("#answer-template").html();t=t.replace("{{PLACE}}",n+".").replace("{{NAME}}",e.user).replace("{{LANGUAGE}}",e.language).replace("{{SIZE}}",e.size).replace("{{LINK}}",e.link),t=jQuery(t),jQuery("#answers").append(t);var o=e.language;/<a/.test(o)&&(o=jQuery(o).text()),s[o]=s[o]||{lang:e.language,user:e.user,size:e.size,link:e.link}});var t=[];for(var o in s)s.hasOwnProperty(o)&&t.push(s[o]);t.sort(function(e,s){return e.lang>s.lang?1:e.lang<s.lang?-1:0});for(var c=0;c<t.length;++c){var i=jQuery("#language-template").html(),o=t[c];i=i.replace("{{LANGUAGE}}",o.lang).replace("{{NAME}}",o.user).replace("{{SIZE}}",o.size).replace("{{LINK}}",o.link),i=jQuery(i),jQuery("#languages").append(i)}}var ANSWER_FILTER="!t)IWYnsLAZle2tQ3KqrVveCRJfxcRLe",COMMENT_FILTER="!)Q2B_A2kjfAiU78X(md6BoYk",answers=[],answers_hash,answer_ids,answer_page=1,more_answers=!0,comment_page;getAnswers();var SCORE_REG=/<h\d>\s*([^\n,]*[^\s,]),.*?(\d+)(?=[^\n\d<>]*(?:<(?:s>[^\n<>]*<\/s>|[^\n<>]+>)[^\n\d<>]*)*<\/h\d>)/,OVERRIDE_REG=/^Override\s*header:\s*/i;
body{text-align:left!important}#answer-list,#language-list{padding:10px;width:290px;float:left}table thead{font-weight:700}table td{padding:5px}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <link rel="stylesheet" type="text/css" href="//cdn.sstatic.net/codegolf/all.css?v=83c949450c8b"> <div id="answer-list"> <h2>Leaderboard</h2> <table class="answer-list"> <thead> <tr><td></td><td>Author</td><td>Language</td><td>Size</td></tr></thead> <tbody id="answers"> </tbody> </table> </div><div id="language-list"> <h2>Winners by Language</h2> <table class="language-list"> <thead> <tr><td>Language</td><td>User</td><td>Score</td></tr></thead> <tbody id="languages"> </tbody> </table> </div><table style="display: none"> <tbody id="answer-template"> <tr><td>{{PLACE}}</td><td>{{NAME}}</td><td>{{LANGUAGE}}</td><td>{{SIZE}}</td><td><a href="{{LINK}}">Link</a></td></tr></tbody> </table> <table style="display: none"> <tbody id="language-template"> <tr><td>{{LANGUAGE}}</td><td>{{NAME}}</td><td>{{SIZE}}</td><td><a href="{{LINK}}">Link</a></td></tr></tbody> </table>

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33 Answers 33

1
2
0
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Python 3, 106 bytes

lambda a:[[a[x][y]*(not(0<x<len(a)-1and 0<y<len(a[0])-1))for y in range(len(a[0]))]for x in range(len(a))]
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0
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05AB1E, 11 bytes

4FøεNĀ*}R}^

Try it online or verify all test cases.

Explanation:

4F       }    # Loop 4 times:
  ø           #  Transpose/zip; swapping rows/columns
   ε   }      #  Map over the matrix (takes the input implicitly in the first iteration)
    NĀ        #   Trutify the index (0 remains 0; everything else becomes 1)
      *       #   Multiply all values in the current row of the matrix with it
        R     #  Reverse the matrix
          ^   # Bitwise-XOR the resulting matrix with the (implicit) input-matrix
              # (and output implicitly)

Example run:

Input:       [[67,4,-8,5,13],[9,13,42,4,-7],[1,1,3,-9,29],[16,99,8,77,0]]

Iteration 1:
 Zip:         [[67,9,1,16],[4,13,1,99],[-8,42,3,8],[5,4,-9,77],[13,-7,29,0]]
 Map:         [[0,0,0,0],[4,13,1,99],[-8,42,3,8],[5,4,-9,77],[13,-7,29,0]]
 Reverse:     [[13,-7,29,0],[5,4,-9,77],[-8,42,3,8],[4,13,1,99],[0,0,0,0]]

Iteration 2:
 Zip:         [[13,5,-8,4,0],[-7,4,42,13,0],[29,-9,3,1,0],[0,77,8,99,0]]
 Map:         [[0,0,0,0,0],[-7,4,42,13,0],[29,-9,3,1,0],[0,77,8,99,0]]
 Reverse:     [[0,77,8,99,0],[29,-9,3,1,0],[-7,4,42,13,0],[0,0,0,0,0]]

Iteration 3:
 Zip:         [[0,29,-7,0],[77,-9,4,0],[8,3,42,0],[99,1,13,0],[0,0,0,0]]
 Map:         [[0,0,0,0],[77,-9,4,0],[8,3,42,0],[99,1,13,0],[0,0,0,0]]
 Reverse:     [[0,0,0,0],[99,1,13,0],[8,3,42,0],[77,-9,4,0],[0,0,0,0]]

Iteration 4:
 Zip:         [[0,99,8,77,0],[0,1,3,-9,0],[0,13,42,4,0],[0,0,0,0,0]]
 Map:         [[0,0,0,0,0],[0,1,3,-9,0],[0,13,42,4,0],[0,0,0,0,0]]
 Reverse:     [[0,0,0,0,0],[0,13,42,4,0],[0,1,3,-9,0],[0,0,0,0,0]]

Bitwise-XOR:  [[67,4,-8,5,13],[9,0,0,0,-7],[1,0,0,0,29],[16,99,8,77,0]]
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-3
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Perl 6, 70 bytes

Whole program that reads columns separated by a space and rows separated by newline. Inplace replacement humbly stolen from b2gills.

my @a=lines.map:{[.split(' ')]};{.[1..*-2]»[1..*-2] »=»0}(@a);dd @a
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1
2

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