Create a data.table From a List in R (2 Examples)
In this R tutorial, you’ll learn how to transform a list into a data.table.
Setting up the Examples
We start by installing and loading the data.table package.
install.packages("data.table") # Install & load data.table library("data.table") |
For the examples, we use the built-in iris dataset.
data(iris) # Load iris data set head(iris) # Sepal.Length Sepal.Width Petal.Length Petal.Width Species # 1 5.1 3.5 1.4 0.2 setosa # 2 4.9 3.0 1.4 0.2 setosa # 3 4.7 3.2 1.3 0.2 setosa # 4 4.6 3.1 1.5 0.2 setosa # 5 5.0 3.6 1.4 0.2 setosa # 6 5.4 3.9 1.7 0.4 setosa |
From the iris data, we construct a list, each list element consists of the first 10 values of one of the variables Sepal.Length, Sepal.Width, and Species.
list_iris <- list(Sepal.Length = iris$Sepal.Length[1:10], Sepal.Width = iris$Sepal.Width[1:10], Species = iris$Species[1:10]) list_iris # $Sepal.Length # [1] 5.1 4.9 4.7 4.6 5.0 5.4 4.6 5.0 4.4 4.9 # # $Sepal.Width # [1] 3.5 3.0 3.2 3.1 3.6 3.9 3.4 3.4 2.9 3.1 # # $Species # [1] setosa setosa setosa setosa setosa setosa setosa setosa setosa setosa # Levels: setosa versicolor virginica |
Example 1: Converting a list to a data.table
In this Example, we use setDT(), which takes a list as input and returns a data.table. Before we apply the function, we create a copy of list l_1 with data.table::copy() as setDT() overrides its input.
iris_dt <- data.table::copy(list_iris) # Replicate list_iris setDT(iris_dt) # Convert iris_dt to a data.table head(iris_dt) # Head of the data # Sepal.Length Sepal.Width Species # 1: 5.1 3.5 setosa # 2: 4.9 3.0 setosa # 3: 4.7 3.2 setosa # 4: 4.6 3.1 setosa # 5: 5.0 3.6 setosa # 6: 5.4 3.9 setosa |
Example 2: Alternative to Converting a list to a data.table
There are other possible ways of turning a list into a data.table. One is to use do.call() and determine that the elements of list_iris are combined columnwise (cbind()) with the following command.
iris_dt2 <- data.table(do.call(cbind, list_iris)) # Convert iris list to a data.table head(iris_dt2) # Head of the data # Sepal.Length Sepal.Width Species # 1: 5.1 3.5 1 # 2: 4.9 3.0 1 # 3: 4.7 3.2 1 # 4: 4.6 3.1 1 # 5: 5.0 3.6 1 # 6: 5.4 3.9 1 |
With outer function data.table(), the output is transformed into a data.table.
Related Articles & Further Resources
Please find some additional R tutorials on topics such as lists, indices, and vectors in the following list.
- Convert Variable of data.table to Vector by Its Index Position
- How to Convert a data.frame to data.table Class in R
- How to Convert List to Unnamed Vector
- How to Convert a Vector to a List
Note: This article was created in collaboration with Anna-Lena Wölwer. Anna-Lena is a researcher and programmer who creates tutorials on statistical methodology as well as on the R programming language. You may find more info about Anna-Lena and her other articles on her profile page.