{"id":861,"date":"2012-04-07T14:42:12","date_gmt":"2012-04-07T14:42:12","guid":{"rendered":"http:\/\/41j.com\/blog\/?p=861"},"modified":"2012-04-07T14:42:12","modified_gmt":"2012-04-07T14:42:12","slug":"select-a-random-line-from-a-file-in-a-single-pass","status":"publish","type":"post","link":"https:\/\/41j.com\/blog\/2012\/04\/select-a-random-line-from-a-file-in-a-single-pass\/","title":{"rendered":"Select a random line from a file in a single pass"},"content":{"rendered":"<pre class=\"brush: cpp; title: ; notranslate\" title=\"\">\r\n#include &lt;iostream&gt;\r\n#include &lt;string&gt;\r\n#include &lt;fstream&gt;\r\n#include &lt;stdlib.h&gt;\r\n#include &lt;vector&gt;\r\n\r\nusing namespace std;\r\n\r\nvoid getrandline(string filename,size_t &amp;selected_line_no,string &amp;selected_line) {\r\n\r\n  ifstream file(filename.c_str());\r\n  selected_line_no = 0;\r\n  for(size_t n=1;!file.eof();n++) {\r\n\r\n    string current_line;\r\n    getline(file,current_line);\r\n\r\n    if(file.eof()) break;\r\n\r\n    if(rand()%n == 0) { selected_line = current_line; selected_line_no = n-1; }\r\n  }\r\n\r\n}\r\n\r\nint main(int argc,char **argv) {\r\n\r\n  srand(time(NULL));\r\n\r\n  vector&lt;size_t&gt; count(100,0); \/\/ just for testing, 100 should be &gt; size of the file...\r\n  for(size_t n=0;n&lt;100000;n++) {\r\n   size_t linenum;\r\n   string line;\r\n   getrandline(argv&#x5B;1],linenum,line);\r\n\r\n   count&#x5B;linenum]++;\r\n   cout &lt;&lt; linenum &lt;&lt; &quot; &quot; &lt;&lt; line &lt;&lt; endl;\r\n  }\r\n\r\n  for(size_t n=0;n&lt;count.size();n++) {\r\n    cout &lt;&lt; n &lt;&lt; &quot; &quot; &lt;&lt; count&#x5B;n] &lt;&lt; endl;\r\n  }\r\n\r\n}\r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"<p>#include &lt;iostream&gt; #include &lt;string&gt; #include &lt;fstream&gt; #include &lt;stdlib.h&gt; #include &lt;vector&gt; using namespace std; void getrandline(string filename,size_t &amp;selected_line_no,string &amp;selected_line) { ifstream file(filename.c_str()); selected_line_no = 0; for(size_t n=1;!file.eof();n++) { string current_line; getline(file,current_line); if(file.eof()) break; if(rand()%n == 0) { selected_line = current_line; selected_line_no = n-1; } } } int main(int argc,char **argv) { srand(time(NULL)); vector&lt;size_t&gt; count(100,0); \/\/ just [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[1],"tags":[],"class_list":["post-861","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p1RRoU-dT","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts\/861","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/comments?post=861"}],"version-history":[{"count":1,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts\/861\/revisions"}],"predecessor-version":[{"id":862,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts\/861\/revisions\/862"}],"wp:attachment":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/media?parent=861"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/categories?post=861"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/tags?post=861"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}