Welcome to the course!
Data Manipulation with data.table in R
Matt Dowle and Arun Srinivasan
Instructors, DataCamp
What is a data.table?
- Enhanced
data.frame- Inherits from and extends
data.frame
- Inherits from and extends
- Columnar data structure
- Every column must be of same length but can be of different type
Why use data.table?
- Concise and consistent syntax
- Think in terms of
rows,columnsandgroups - Provides a placeholder for each
- Think in terms of
# General form of data.table syntax
DT[i, j, by]
| | |
| | --> grouped by what?
| -----> what to do?
--------> on which rows?
Why use data.table?
- Feature-rich
- Parallelization
- Fast updates by reference
- Powerful joins (Joining Data with data.table in R)
Creating a data.table
Three ways of creating data tables:
data.table()as.data.table()fread()
Creating a data.table
library(data.table)
x_df <- data.frame(id = 1:2, name = c("a", "b"))
x_df
id name
1 a
2 b
x_dt <- data.table(id = 1:2, name = c("a", "b"))
x_dt
id name
1 a
2 b
Creating a data.table
y <- list(id = 1:2, name = c("a", "b"))
y
$id
1 2
$name
"a" "b"
x <- as.data.table(y)
x
id name
1 a
2 b
data.tables and data.frames (I)
Since a data.table is a data.frame ...
x <- data.table(id = 1:2,
name = c("a", "b"))
x
id name
1 a
2 b
class(x)
"data.table" "data.frame"
data.tables and data.frames (II)
Functions used to query data.frames also work on data.tables
nrow(x)
2
ncol(x)
2
dim(x)
2 2
data.tables and data.frames (III)
A data table never automatically converts character columns to factors
x_df <- data.frame(id = 1:2, name = c("a", "b"))
class(x_df$name)
"factor"
x_dt <- data.table(id = 1:2, name = c("a", "b"))
class(x_dt$name)
"character"
data.tables and data.frames (IV)
Never sets, needs or uses row names
rownames(x_dt) <- c("R1", "R2")
x_dt
id name
1: 1 a
2: 2 b
Let's practice!
Data Manipulation with data.table in R
