109 lines
2.4 KiB
Org Mode
109 lines
2.4 KiB
Org Mode
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#+TITLE: Datatable package
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#+DATE: 2021-10-26
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#+OPTIONS: creator:nil timestamp:nil todo:nil num:nil
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#+PROPERTY: header-args:R :results output :session *Rc* :cmdline :tangle yes
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#+PROPERTY: header-args:R+ :exports both
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#+SETUPFILE: https://fniessen.github.io/org-html-themes/org/theme-readtheorg.setup
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#+HTML_HEAD: <style> #content{max-width:1800px;}</style>
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#+HTML_HEAD: <style> p{max-width:800px;}</style>
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#+HTML_HEAD: <style> li{max-width:800px;}</style>
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#+HTML_HEAD: <style> pre.src{background: #f5f5f5;color:black;}</style>
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#+HTML_HEAD: <style> .example{background: #fefefa;color:black;}</style>
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#+begin_export html
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<div id="subtitle" style="float: center; text-align: center;">
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<p>
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Org document with
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<a href="http://www.r-project.org/">R</a> code
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</p>
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<p>
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<a href="http://www.r-project.org/">
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<img src="http://www.r-project.org/Rlogo.jpg"/>
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</a>
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</p>
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</div>
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#+end_export
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#+begin_src R :exports code
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rm(list = ls())
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#+end_src
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** Select columns in "j"
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This creates a vector
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#+begin_src R
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dt_c <- flights[, arr_delay]
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head(dt_c)
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#+end_src
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To create a data.table, use the function "~list~" or dot "~.~"
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#+begin_src R
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dt_c1 <- flights[, list(arr_delay)]
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head(dt_c1)
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#+end_src
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The selection is wrapped in "~list~", thus, the columns can be
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renamed
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#+begin_src R
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dt_c2 <- flights[, .(delay2arriv = arr_delay, dist = distance)]
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head(dt_c2)
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#+end_src
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#+begin_src R
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dt_c2a <- flights[, c("arr_delay", "distance")]
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head(dt_c2a)
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#+end_src
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#+begin_src R
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dt_c2b <- flights[, year:day]
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head(dt_c2b)
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#+end_src
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Building new colummns
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#+begin_src R
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head(dt_c2b[, `:=`(time = year -1, # name = value,
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pumpkin = month,
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tomatoe = day +1)])
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#+end_src
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Renaming colummns
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#+begin_src R
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setnames(dt_c2b,
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c("time", "pumpkin", "tomatoe"),# old names
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c("time_minus1", "pumpkin_month", "day_plus1")) # new names
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names(dt_c2b)
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#+end_src
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#+begin_src R
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setnames(dt_c2b, toupper) # new names
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names(dt_c2b)
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#+end_src
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Renaming colummns
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#+begin_src R
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setnames(dt_c2b, tolower) # new names
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names(dt_c2b)
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#+end_src
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#+begin_src R
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dt_c2c <- flights[, -(year:day)]
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head(dt_c2c)
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#+end_src
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Select columns by patterns, e.g., selecting 5 lines form columns having "del"
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characters in the name:
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#+begin_src R
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flights[1:5, names(flights) %like% "del", with = FALSE]
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#+end_src
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