The “top_n” Function in R

• Package: dplyr

• Purpose: To select the top (or bottom) n rows within each group based on a specified variable.

• General Class: Data Manipulation

• Required Argument(s):

• data: The data frame to filter.

• n: The number of rows to select within each group.

• Notable Optional Arguments:

• wt: A variable to use for ordering rows within each group.

• ...: Additional arguments passed to the ordering function.

• Example (with Explanation):

• # Load necessary packages
  library(dplyr)
  
  # Create a sample data frame
  data <- data.frame(
  ID = c(1, 2, 3, 4, 5, 6, 7),
  group = c("A", "A", "B", "B", "C", "C", "C"),
  value = c(10, 15, 20, 25, 30, 35, 40)
  )
  
  # Select the top 2 rows within each group based on 'value'
  result <- data %>%
  group_by(group) %>%
  top_n(2, wt = value)
  
  # Display the result
  print(result)

• In this example, the top_n function from the dplyr package is used to select the top 2 rows within each group defined by the ‘group’ column in the sample data frame data. The selection is based on the ‘value’ column, with higher values considered to be at the top. The result is a new data frame result containing the top 2 rows within each group based on the specified criteria.