#+TITLE: Datatable package
#+DATE: 2021-10-26
#+OPTIONS: creator:nil timestamp:nil todo:nil num:nil
#+PROPERTY: header-args:R :results output :session *Rc* :cmdline :tangle yes
#+PROPERTY: header-args:R+ :exports both
#+SETUPFILE: https://fniessen.github.io/org-html-themes/org/theme-readtheorg.setup
#+HTML_HEAD: <style> #content{max-width:1800px;}</style>
#+HTML_HEAD: <style> p{max-width:800px;}</style>
#+HTML_HEAD: <style> li{max-width:800px;}</style>
#+HTML_HEAD: <style> pre.src{background: #f5f5f5;color:black;}</style>
#+HTML_HEAD: <style> .example{background: #fefefa;color:black;}</style>


#+begin_export html
  <div id="subtitle" style="float: center; text-align: center;">
    <p>
      Org document with
      <a href="http://www.r-project.org/">R</a> code
    </p>
    <p>
      <a href="http://www.r-project.org/">
	<img src="http://www.r-project.org/Rlogo.jpg"/>
      </a>
    </p>
  </div>
#+end_export

#+begin_src R :exports code
  rm(list = ls())
#+end_src


** Querying data.table

Sintaxis:

 * ~DT[i, j, by]~

Subseting by "i" and "j"

** Subset rows in "i"

#+begin_src R
  dt1 <- flights[origin == "JFK" & month == 6L]
  dt1
#+end_src

Get the first two rows

#+begin_src R
  flights[1:2]
#+end_src

#+RESULTS:
:    year month day dep_delay arr_delay carrier origin dest air_time distance
: 1: 2014     1   1        14        13      AA    JFK  LAX      359     2475
: 2: 2014     1   1        -3        13      AA    JFK  LAX      363     2475
:    hour
: 1:    9
: 2:   11

Ordering results of querying

#+begin_src R
  dt_filt <- flights[order(origin, -dest)]
  dt_filt
#+end_src