Print dataframe to console during intermediate steps in dplyr chain

user_372526 0
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While debugging dplyr chains in a function, I often want to be able to print intermediate changes to a data.frame to the console. How would I do this?

For example:

data(cars)
cars %>% group_by(speed) %>% 
  summarize(dist_mean = mean(dist)) %>%
  [insert printing function] %>% 
  group_by(speed > 10) %>%
  summarize(dist_mean = mean(dist_mean)) %>%
  [insert printing function]

Is there something I can do to replace [insert printing function] to print the current state of the dataframe to the console, while still continuing the chain uninterrupted?

dplyr r
1 Answers

Try the T-pipe: %T>%.

From documentation:

Pipe a value forward into a function- or call expression and return the original value instead of the result. This is useful when an expression is used for its side-effect, say plotting or printing.

There is a good example of it here along with the other two less common pipe commands.

Inserting back into your original context:

data(cars)
cars %>% group_by(speed) %>% 
  summarize(dist_mean = mean(dist)) %T>%
  print() %>% 
  group_by(speed > 10) %>%
  summarize(dist_mean = mean(dist_mean)) %T>%
  print()

Edit: As per @Ritchie Sacramento's comment the pipes are part of the magrittr package. They also appear to be re-exported by dplyr. If they don't work after calling library(dplyr) then you will need to call library(magrittr) to access them.

user_77429810
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