{"id":24766,"date":"2022-12-05T15:26:13","date_gmt":"2022-12-05T09:56:13","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-using-group_by-in-dplyr-for-certain-number-of-rows\/"},"modified":"2022-12-05T15:26:13","modified_gmt":"2022-12-05T09:56:13","slug":"solved-using-group_by-in-dplyr-for-certain-number-of-rows","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-using-group_by-in-dplyr-for-certain-number-of-rows\/","title":{"rendered":"[Solved] Using group_by() in dplyr for certain number of rows"},"content":{"rendered":"<p> [ad_1]<br \/>\n<\/p>\n<div id=\"answer-35567739\" class=\"answer js-answer accepted-answer js-accepted-answer\" data-answerid=\"35567739\" data-parentid=\"35567629\" data-score=\"2\" data-position-on-page=\"1\" data-highest-scored=\"1\" data-question-has-accepted-highest-score=\"1\" itemprop=\"acceptedAnswer\" itemscope itemtype=\"https:\/\/schema.org\/Answer\">\n<div class=\"post-layout\">\n<div class=\"votecell post-layout--left\"><\/div>\n<div class=\"answercell post-layout--right\">\n<div class=\"s-prose js-post-body\" itemprop=\"text\">\n<p>You just want to group on-the-fly, which means passing an <em>ad hoc<\/em> variable to the grouper.<\/p>\n<p>In <code>data.table<\/code>, this would be done by using <code>rep<\/code> in <code>by<\/code>:<\/p>\n<pre><code>library(data.table)\nset.seed(01394)\nDT &lt;- data.table(VAR = rnorm(2520))\n\nDT[ , mean(VAR), by = rep(1:18, each = 140)]\n#     rep           V1\n#  1:   1  0.029683200\n#  2:   2  0.150411987\n#  3:   3  0.061912697\n#  4:   4 -0.014229183\n#  5:   5 -0.007305455\n#  6:   6  0.003784550\n#  7:   7  0.010941501\n#  8:   8  0.032129151\n#  9:   9 -0.036524921\n# 10:  10  0.046986451\n# 11:  11  0.075547228\n# 12:  12 -0.079538420\n# 13:  13 -0.099833001\n# 14:  14 -0.065297462\n# 15:  15 -0.020778063\n# 16:  16  0.095983764\n# 17:  17  0.095292230\n# 18:  18  0.150405148\n<\/code><\/pre>\n<hr>\n<p>As per @docendodecimus, the <code>dplyr<\/code> equivalent is:<\/p>\n<pre><code>DT %&gt;% group_by(g = rep(1:18, each = 140)) %&gt;% summarise(m = mean(VAR))\n<\/code><\/pre>\n<\/p><\/div>\n<div class=\"mt24\"><\/div>\n<\/div>\n<p>            <span class=\"d-none\" itemprop=\"commentCount\">0<\/span> <\/p><\/div>\n<\/div>\n<p>[ad_2]<\/p>\n<p>solved Using group_by() in dplyr for certain number of rows <\/p>\n","protected":false},"excerpt":{"rendered":"<p>[ad_1] You just want to group on-the-fly, which means passing an ad hoc variable to the grouper. In data.table, this would be done by using rep in by: library(data.table) set.seed(01394) DT &lt;- data.table(VAR = rnorm(2520)) DT[ , mean(VAR), by = rep(1:18, each = 140)] # rep V1 # 1: 1 0.029683200 # 2: 2 0.150411987 &#8230; <a title=\"[Solved] Using group_by() in dplyr for certain number of rows\" class=\"read-more\" href=\"https:\/\/jassweb.com\/solved\/solved-using-group_by-in-dplyr-for-certain-number-of-rows\/\" aria-label=\"More on [Solved] Using group_by() in dplyr for certain number of rows\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[1256,321,707],"class_list":["post-24766","post","type-post","status-publish","format-standard","hentry","category-solved","tag-dplyr","tag-r","tag-sqlite"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>[Solved] Using group_by() in dplyr for certain number of rows - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-using-group_by-in-dplyr-for-certain-number-of-rows\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] Using group_by() in dplyr for certain number of rows - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] You just want to group on-the-fly, which means passing an ad hoc variable to the grouper. In data.table, this would be done by using rep in by: library(data.table) set.seed(01394) DT &lt;- data.table(VAR = rnorm(2520)) DT[ , mean(VAR), by = rep(1:18, each = 140)] # rep V1 # 1: 1 0.029683200 # 2: 2 0.150411987 ... 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In data.table, this would be done by using rep in by: library(data.table) set.seed(01394) DT &lt;- data.table(VAR = rnorm(2520)) DT[ , mean(VAR), by = rep(1:18, each = 140)] # rep V1 # 1: 1 0.029683200 # 2: 2 0.150411987 ... 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