Lossy Sorting (Implement Dropsort)

Question

Dropsort, designed by David Morgan-Mar, is an example of a linear-time "sorting algorithm" that produces a list that is, in fact, sorted, but contains only some of the original elements. Any element that is not at least as large as the maximum of the elements preceding it is simply removed from the list and discarded.

In this task, you will be given a list of integers as input (STDIN or function argument, you are required to support at least the range of 8-bit signed integers.) Your task is to dropsort them and then output the remaining elements in order.

You may assume that the list is non-empty.

This is code-golf, so the shortest program wins.

Test Cases

Input             Output
1 2 5 4 3 7       1 2 5 7
10 -1 12          10 12
-7 -8 -5 0 -1 1   -7 -5 0 1
9 8 7 6 5         9
10 13 17 21       10 13 17 21
10 10 10 9 10     10 10 10 10

Leaderboard

var QUESTION_ID=61808,OVERRIDE_USER=39022;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>

Answer 1

Clojure, 55 bytes

#(for[[i j](map list(reductions max %)%):when(= i j)]j)

One day I'm gonna do a "Golfure" or something of that short which will have one-symbol names for most handy functions, and even more generic macros.

Answer 2

C++ (gcc), 122 119 bytes

-3 bytes thanx to ceilingcat

#include<list>
auto f(std::list<int>l){auto i=l.begin();for(int m=*i;i!=l.end();)i=*i>=m?m=*i,++i:l.erase(i);return l;}

Try it online!

Answer 3

Python 3, 68 64 62 bytes

lambda L:[L[i]for i in range(len(L))if L[i]>=max(L[:1]+L[:i])]

Try it online!

Answer 4

JavaScript, 7270 bytes

a=>{for(b=[a[l=i=0]];i<a.length;b[l]>=a[++i]?b[++l]=a[i]:0);return a}

72B->70B - -2B for removing assignment of the function.

Answer 5

MathGolf, 10 bytes

╓\ô`╙┼=╛o╘

Try it online!

This solution relies on stack manipulation. It could have been 2 bytes shorter if negative numbers are not included (skip the first two bytes). Basically a port of the 05AB1E answer, except there is more of a hassle to get the stack right.

Explanation

╓            minimum of two elements, min of list, minimum by filter
 \           swap top elements, pushing list to top
  ô          start block of length 6
   `         duplicate the top two items
    ╙        maximum of two elements, max of list, maximum by filter
     ┼       duplicate second item from top and push to top
      =      is equal (is the current element equal to the total maximum so far)
       ╛o    print without popping if equal
             loop ends here
         ╘   discard everything in stack

Answer 6

Perl 5.10.0 -n, 17 16 15 bytes

$m>$_||say$m=$_

Try it online!

-1 byte thanks to Xcali

Answer 7

Pushy, 14 bytes

@vL:Ov2d>?.;;_

Try it online!

                     \ Implicit: input on main stack.
@                    \ Reverse stack.
 v                   \ Move top item to auxiliary stack.
  L:        ;        \ length(main stack) times do:
    Ov               \   Move top item from main stack to auxiliary stack.
      2d>? ;         \   If top element > second element:
          .          \       Pop the main stack element.
             _       \ Output stack.

Answer 8

Factor, 41 bytes

[ -1/0. swap [ 2dup max -rot > ] reject ]

Attempt This Online!

Answer 9

Nekomata, 4 bytes

pƆᵖ≤

Attempt This Online!

pƆᵖ≤
p       For all prefixes of the input
 Ɔ      Split it into the last element and the rest
  ᵖ≤    Check if the last element is greater than or equal to the rest
        If so, the last element is returned