Which of the following statements about working with data tables is not true?

data.table provides a high-performance version of base R's data.frame with syntax and feature enhancements for ease of use, convenience and programming speed.

Why data.table?

• concise syntax: fast to type, fast to read
• fast speed
• memory efficient
• careful API lifecycle management
• community
• feature rich

Features

• fast and friendly delimited file reader: ?fread, see also convenience features for small data
• fast and feature rich delimited file writer: ?fwrite
• low-level parallelism: many common operations are internally parallelized to use multiple CPU threads
• fast and scalable aggregations; e.g. 100GB in RAM (see benchmarks on up to two billion rows)
• fast and feature rich joins: ordered joins (e.g. rolling forwards, backwards, nearest and limited staleness), overlapping range joins (similar to IRanges::findOverlaps), non-equi joins (i.e. joins using operators >, >=, <, <=), aggregate on join (by=.EACHI), update on join
• fast add/update/delete columns by reference by group using no copies at all
• fast and feature rich reshaping data:

  library(data.table)
  DT = as.data.table(iris)
  
  # FROM[WHERE, SELECT, GROUP BY]
  # DT  [i,     j,      by]
  
  DT[Petal.Width > 1.0, mean(Petal.Length), by = Species]
  #      Species       V1
  #1: versicolor 4.362791
  #2:  virginica 5.552000

  0 (pivot/wider/spread) and

  library(data.table)
  DT = as.data.table(iris)
  
  # FROM[WHERE, SELECT, GROUP BY]
  # DT  [i,     j,      by]
  
  DT[Petal.Width > 1.0, mean(Petal.Length), by = Species]
  #      Species       V1
  #1: versicolor 4.362791
  #2:  virginica 5.552000

  1 (unpivot/longer/gather)
• any R function from any R package can be used in queries not just the subset of functions made available by a database backend, also columns of type

  library(data.table)
  DT = as.data.table(iris)
  
  # FROM[WHERE, SELECT, GROUP BY]
  # DT  [i,     j,      by]
  
  DT[Petal.Width > 1.0, mean(Petal.Length), by = Species]
  #      Species       V1
  #1: versicolor 4.362791
  #2:  virginica 5.552000

  2 are supported
• has no dependencies at all other than base R itself, for simpler production/maintenance
• the R dependency is as old as possible for as long as possible, dated April 2014, and we continuously test against that version; e.g. v1.11.0 released on 5 May 2018 bumped the dependency up from 5 year old R 3.0.0 to 4 year old R 3.1.0

Installation

install.packages("data.table")

# latest development version that has passed all tests:
data.table::update_dev_pkg()

See the Installation wiki for more details.

Usage

Use data.table subset

library(data.table)
DT = as.data.table(iris)

# FROM[WHERE, SELECT, GROUP BY]
# DT  [i,     j,      by]

DT[Petal.Width > 1.0, mean(Petal.Length), by = Species]
#      Species       V1
#1: versicolor 4.362791
#2:  virginica 5.552000

• no need to prefix each column with

  library(data.table)
  DT = as.data.table(iris)
  
  # FROM[WHERE, SELECT, GROUP BY]
  # DT  [i,     j,      by]
  
  DT[Petal.Width > 1.0, mean(Petal.Length), by = Species]
  #      Species       V1
  #1: versicolor 4.362791
  #2:  virginica 5.552000

  6 (like

  library(data.table)
  DT = as.data.table(iris)
  
  # FROM[WHERE, SELECT, GROUP BY]
  # DT  [i,     j,      by]
  
  DT[Petal.Width > 1.0, mean(Petal.Length), by = Species]
  #      Species       V1
  #1: versicolor 4.362791
  #2:  virginica 5.552000

  7 and

  library(data.table)
  DT = as.data.table(iris)
  
  # FROM[WHERE, SELECT, GROUP BY]
  # DT  [i,     j,      by]
  
  DT[Petal.Width > 1.0, mean(Petal.Length), by = Species]
  #      Species       V1
  #1: versicolor 4.362791
  #2:  virginica 5.552000

  8 but built-in)
• any R expression using any package is allowed in

  library(data.table)
  DT = as.data.table(iris)
  
  # FROM[WHERE, SELECT, GROUP BY]
  # DT  [i,     j,      by]
  
  DT[Petal.Width > 1.0, mean(Petal.Length), by = Species]
  #      Species       V1
  #1: versicolor 4.362791
  #2:  virginica 5.552000

  9 argument, not just list of columns
• extra argument data.table0 to compute

  library(data.table)
  DT = as.data.table(iris)
  
  # FROM[WHERE, SELECT, GROUP BY]
  # DT  [i,     j,      by]
  
  DT[Petal.Width > 1.0, mean(Petal.Length), by = Species]
  #      Species       V1
  #1: versicolor 4.362791
  #2:  virginica 5.552000

  9 expression by group

library(data.table)
DT = as.data.table(iris)

# FROM[WHERE, SELECT, GROUP BY]
# DT  [i,     j,      by]

DT[Petal.Width > 1.0, mean(Petal.Length), by = Species]
#      Species       V1
#1: versicolor 4.362791
#2:  virginica 5.552000

Getting started

• Introduction to data.table vignette
• Getting started wiki page
• produced by data.table2

Cheatsheets

Community

data.table is widely used by the R community. It is being directly used by hundreds of CRAN and Bioconductor packages, and indirectly by thousands. It is one of the top most starred R packages on GitHub, and was highly rated by the Depsy project. If you need help, the data.table community is active on StackOverflow.

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