Why will this R pipe run but not this one?-CodePudding

We began by loading the 'palmerpenguins' data set from the tidyverse package.

library(tidyverse)
library(palmerpenguins)

This is the code that will run:

penguins %>% group_by(island) %>% drop_na() %>% summarise(mean_bill_length_mm = mean(bill_length_mm))

Why will this same code but with tabs and indention not run?

penguins %>% group_by(island) 
  %>% drop_na() 
  %>% summarise(mean_bill_length_mm = mean(bill_length_mm))

When I run this code I get the following error:

Error: unexpected SPECIAL in " %>%"

CodePudding user response：

You've probably seen code from other programming languages where every line ends with a semicolon ;. R doesn't require that (though you actually can use semicolons to indicate line endings in R).

Instead, the R interpreter is always looking for a valid line-ending when a command looks "complete", and then it assumes the command has ended, it executes it, and expects the next line to start a new command.

So in R, we can do this:

## this works
1 * 2 *
3
# [1] 6

R knows to expect more code after a *. You can't end a valid statement with *, so, even though there's a line break, R is expecting the command to continue.

But this is an error:

1 * 2
* 3
# Error: unexpected '*' in "  *"

1 * 2 is perfectly valid. R has no reason to expect the command to continue, so 1 * 2 is run, and then R expects the next line to be a new command. But * 3 isn't valid syntax, so there is an error.

Your pipe is just the same:

penguins %>% group_by(island)  
      ## this looks like a complete command!
  %>% drop_na()               
      ## this looks like a new line starting with %>%
      ## (which is an Error, because you need something before a pipe)
# Error: unexpected SPECIAL in " %>%"

So, when using pipes, you need to use the pipe at the end of each line to tell R that that line is going to continue.