Select first and last row from grouped data

📝 Tech Blog Post: Selecting the First and Last Row from Grouped Data in R using dplyr

<p>Greetings, fellow data wranglers! 👋 In today's blog post, we'll dive into a common problem faced by R users when working with grouped data. Have you ever wondered how to select the first and last row of each group using the mighty `dplyr` package? 🤔 Well, fret no more! We've got you covered with easy-to-implement solutions to save you time and effort. Let's get started! 💪</p>

The Problem

Consider you have a data frame called df with multiple groups and you want to extract the first and last rows of each group based on a specific criteria. Let's take a look at an example:

df <- data.frame(
  id = c(1,1,1,2,2,2,3,3,3),
  stopId = c("a", "b", "c", "a", "b", "c", "a", "b", "c"),
  stopSequence = c(1,2,3,3,1,4,3,1,2)
)

In the provided example, we have three groups of data, identified by the id column. Our goal is to select the first and last rows based on the stopSequence within each group.

The Solution

Fortunately, the dplyr package offers a convenient way to tackle this problem using the slice() function in combination with the arrange() function.

To select the first row of each group, we can use the following code:

firstStop <- df %>%
  group_by(id) %>%
  arrange(stopSequence) %>%
  slice(1) %>%
  ungroup()

Similarly, to select the last row of each group, we can adapt the code slightly:

lastStop <- df %>%
  group_by(id) %>%
  arrange(stopSequence) %>%
  slice(n()) %>%
  ungroup()

Now comes the exciting part — combining these two statements into a single line of code to select both the first and last rows simultaneously! 😎

firstAndLastStop <- df %>%
  group_by(id) %>%
  arrange(stopSequence) %>%
  slice(c(1, n())) %>%
  ungroup()

By using the c() function within the slice() function, we can specify the indices of the desired rows within each group. In our case, c(1, n()) represents the first and last indices of each group.

Simplify Your Code

Now, you can impress your colleagues with this powerful one-liner that efficiently selects the first and last rows from grouped data using dplyr. 🎉

Remember, time is precious, so optimizing your code can boost your productivity and make you the hero of your data analysis projects! ⏰💪

Wrap Up and Take Action

Armed with this newfound knowledge, you can now confidently retrieve the first and last rows of grouped data using dplyr in R. 🚀

Next time you encounter a similar problem, give this technique a try and amaze your peers with your coding wizardry! ✨

If you found this blog post helpful, don't forget to share it with fellow data enthusiasts. Sharing is caring, after all! ❤️

Got any questions or suggestions for future blog posts? Leave a comment below and let's start a discussion! 👇 We'd love to hear from you. Happy coding! 💻😃

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