Documentation

data.table

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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: ?dcast (pivot/wider/spread) and ?melt (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 list 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 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")

Development version

install.packages("data.table", repos="https://Rdatatable.gitlab.io/data.table")

or update only if newer revision is available

data.table::update.dev.pkg()

See the Installation wiki for more details.

Usage

Use data.table subset [ operator the same way you would use data.frame one, but...

  • no need to prefix columns with DT$
  • any valid expression is allowed in j argument
  • extra argument by to compute j 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

Cheatsheets

Community

data.table is widely used by the R community. As of July 2019, it was used by over 680 CRAN and Bioconductor packages and was the 9th most starred R package on GitHub. If you need help, the data.table community is active StackOverflow, with nearly 9,000 questions.

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Contributing

Guidelines for filing issues / pull requests: Contribution Guidelines.