Convert large list to dataframe in R

In this article, we will discuss how to convert a large list to a dataframe in the R Programming Language. 

Method 1 : Using rbindlist()

First, create a large list. Then use the Map function on the list and convert it to dataframe using the as.data.frame function in R. The map function applies a function and transforms the given input to each element of a list or vector. We will be using as.data.frame function inside the map to convert each element of a given list to a dataframe.

After mapping and converting each element of the list to a dataframe, the next step is to take the entire large list and convert it to a data table or dataframe using the rbindlist function in R.

Syntax : 

rbindlist( l, fill = FALSE, use.names = "check", idcol = NULL)

Parameters :

• l : This is a list of data.table or data.frame or list objects.
• fill : This is false by default. If we specify this as true, then it automatically fills the missing columns with NAs.
• use.names : By default, it is specified as check which implies all the elements may not have same names in the same order. If it is specified as true, then we bind by matching column names and if false, then we bind by matching positions.
• idcol : It basically creates a column in the result, displaying which list item those particular rows came from.

You can also use system.time() function to calculate the elapsed time for conversion.

Example: Converting a large list to dataframe using rbindlist() method

library(Matrix)
library(data.table)

# Creating the large list
data <- matrix(data = 1, nrow = 300, ncol = 3)
list_data <- rep(list(data), 18000)

# Mapping -> converting the list to 
# dataframe
list_data <- Map(as.data.frame, list_data)

# Converting the large list to dataframe
# using the rbindlist function
datarbind <- rbindlist(list_data)

# Print the dataframe
datarbind

Output :

Method 2: Using plyr package

We will be using ldply() function of the 'plyr' package. 

Syntax: ldply(large_list)

Parameter:

large_list: pass your large list

Import the required packages, then pass your list which you want to convert to a dataframe into ldply() function as an argument.

Example: Converting a large list to dataframe using plyr package

library(Matrix)
library(plyr)

# Creating the large list
data <- matrix(data = 1, nrow = 300, ncol = 3)

# Replicating the list
list_data <- rep(list(data), 18000)

ldply(list_data)

Output:

  1 2 3
1     1 1 1
2     1 1 1
3     1 1 1
4     1 1 1
5     1 1 1
6     1 1 1
7     1 1 1
8     1 1 1
9     1 1 1
10    1 1 1
11    1 1 1
12    1 1 1
13    1 1 1
14    1 1 1
15    1 1 1
16    1 1 1
17    1 1 1
18    1 1 1
.
.
.