Stepping through a pipeline with intermediate results

Question

Is there a way to output the result of a pipeline at each step without doing it manually? (eg. without selecting and running only the selected chunks)

I often find myself running a pipeline line-by-line to remember what it was doing or when I am developing some analysis.

For example:

library(dplyr)

mtcars %>% 
  group_by(cyl) %>% 
  sample_frac(0.1) %>% 
  summarise(res = mean(mpg))
# Source: local data frame [3 x 2]
# 
# cyl  res
# 1   4 33.9
# 2   6 18.1
# 3   8 18.7

I'd to select and run:

mtcars %>% group_by(cyl)

and then...

mtcars %>% group_by(cyl) %>% sample_frac(0.1)

and so on...

But selecting and CMD/CTRL+ENTER in RStudio leaves a more efficient method to be desired.

Can this be done in code?

Is there a function which takes a pipeline and runs/digests it line by line showing output at each step in the console and you continue by pressing enter like in demos(...) or examples(...) of package guides

Answer 1

You can select which results to print by using the tee-operator (%T>%) and print(). The tee-operator is used exclusively for side-effects like printing.

# i.e.
mtcars %>%
  group_by(cyl) %T>% print() %>%
  sample_frac(0.1) %T>% print() %>%
  summarise(res = mean(mpg))