Adding {data.table} tutorial
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@ -40,3 +40,9 @@ data using the R programming environment
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* [[./script/roadoi_package.R]['roadoi']]
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* [[./script/scraping.R]['crul' package - web scraping]]
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** Data wrangling with {data.table}
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* [[./doc/datatable_intro.org][Introduction to {data.table}]]
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* [[./doc/datatable_querying.org][Querying in {data.table}: filter in ~i~ ]]
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* [[./doc/datatable_querying_j.org][Querying in {data.table}: select in ~j~ ]]
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90
doc/datatable_intro.org
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90
doc/datatable_intro.org
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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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** Introduction
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#+begin_src R
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library(data.table)
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#+end_src
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Reading data into R using ~{data.table}~
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#+begin_src R :exports code
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url = "https://raw.githubusercontent.com/Rdatatable/data.table/master/vignettes/flights14.csv"
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flights <- fread(url)
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#+end_src
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#+RESULTS:
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#+begin_src R
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names(flights)
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#+end_src
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#+begin_src R
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flights
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#+end_src
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#+begin_src R
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nrow(flights)
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#+end_src
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#+RESULTS:
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: [1] 253316
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Creating a data.table:
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#+begin_src R
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dt <- data.table(col1 = c(1:6),
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col2 = LETTERS[1:6],
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col3 = (1))
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#+end_src
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#+begin_src R
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class(dt)
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#+end_src
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#+begin_src R
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class(dt$col2)
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#+end_src
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** Some references to learn more about {data.table}
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* https://cran.r-project.org/web/packages/data.table/vignettes/datatable-intro.html
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* See vignettes in R:
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: > vignette(package="data.table")
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* https://atrebas.github.io/post/2019-03-03-datatable-dplyr/
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* https://rdatatable.gitlab.io/data.table/
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* https://s3.amazonaws.com/assets.datacamp.com/blog_assets/datatable_Cheat_Sheet_R.pdf
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* https://stackoverflow.com/questions/21435339/data-table-vs-dplyr-can-one-do-something-well-the-other-cant-or-does-poorly
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* ~dtplyr~ package:
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* https://github.com/tidyverse/dtplyr
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67
doc/datatable_querying.org
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67
doc/datatable_querying.org
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@ -0,0 +1,67 @@
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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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** Querying data.table
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Sintaxis:
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* ~DT[i, j, by]~
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Subseting by "i" and "j"
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** Subset rows in "i"
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#+begin_src R
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dt1 <- flights[origin == "JFK" & month == 6L]
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dt1
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#+end_src
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Get the first two rows
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#+begin_src R
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flights[1:2]
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#+end_src
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#+RESULTS:
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: year month day dep_delay arr_delay carrier origin dest air_time distance
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: 1: 2014 1 1 14 13 AA JFK LAX 359 2475
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: 2: 2014 1 1 -3 13 AA JFK LAX 363 2475
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: hour
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: 1: 9
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: 2: 11
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Ordering results of querying
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#+begin_src R
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dt_filt <- flights[order(origin, -dest)]
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dt_filt
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#+end_src
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108
doc/datatable_querying_j.org
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108
doc/datatable_querying_j.org
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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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