Often you may want to select the first row in each group using the dplyr package in R. You can use the following basic syntax to do so:

df %>% group_by(group_var) %>% arrange(values_var) %>% filter(row_number()==1)

The following example shows how to use this function in practice.

**Example: Select the First Row by Group in R**

Suppose we have the following dataset in R:

#create dataset df <- data.frame(team=c('A', 'A', 'A', 'B', 'B', 'B', 'C', 'C', 'C', 'C'), points=c(4, 9, 7, 7, 6, 13, 8, 8, 4, 17)) #view dataset df team points 1 A 4 2 A 9 3 A 7 4 B 7 5 B 6 6 B 13 7 C 8 8 C 8 9 C 4 10 C 17

The following code shows how to use the dplyr package to select the first row by group in R:

library(dplyr) df %>% group_by(team) %>% arrange(points) %>% filter(row_number()==1) # A tibble: 3 x 2 # Groups: team [3] team points 1 A 4 2 C 4 3 B 6

By default, **arrange()** sorts the values in ascending order but we can easily sort the values in descending order instead:

df %>% group_by(team) %>% arrange(desc(points)) %>% filter(row_number()==1) # A tibble: 3 x 2 # Groups: team [3] team points 1 C 17 2 B 13 3 A 9

Note that you can easily modify this code to select the n^{th} row by each group. Simply change **row_number() == n**.

For example, if you’d like to select the 2nd row by group, you can use the following syntax:

df %>% group_by(team) %>% arrange(desc(points)) %>% filter(row_number()==2)

Or you could use the following syntax to select the last row by group:

df %>% group_by(team) %>% arrange(desc(points)) %>% filter(row_number()==n())

**Additional Resources**

How to Arrange Rows in R

How to Count Observations by Group in R

How to Find the Maximum Value by Group in R