Printing intermediate results without breaking pipeline in tidyverse

You could easily write your own function

pass_through <- function(data, fun) {fun(data); data}

And use it like

mtcars %>% pass_through(. %>% ncol %>% print) %>% nrow

Here we use the . %>% syntax to create an anonymous function. You could also write your own more explicitly with

mtcars %>% pass_through(function(x) print(ncol(x))) %>% nrow

Fleshing out MrFlick's answer for the print case where it's even simpler:

# Your pipe-print function
pipe_print = function(data) {print(data); data}

# Let's try it in action:
mtcars %>% 
    mutate(kmpl = 0.425*mpg) %>%  # Convert to km-per-liter
    pipe_print() %>%  # Pipe print! Did it work?
    group_by(cyl) %>%  # Continue processing...
    summarise(mpg = mean(mpg))

You can do on the fly with an anonymous function:

mtcars %>% ( function(x){print(x); return(x)} ) %>% nrow()