How to compare the number of rows in a pipeline in r?-CodePudding

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

#from Printing intermediate results without breaking pipeline in tidyverse answer

mtcars %>% filter(mpg>15) %>% pass_through(. %>% nrow %>% print)

From the code above, I can print the number of rows of the data after filtering. But I cannot print the difference of number of rows between the original data and the data after filtering.

> mtcars %>% filter(mpg>15) %>% pass_through(. %>% nrow %>% print(.-nrow(mtcars)))

Error in print.default(., . - nrow(mtcars)) : invalid printing digits -6

Question 1: Are there any ways to check the difference without using any extra variables and breaking pipeline?

Question 2: Are there any ways to check the difference between 'n'th pipeline and 'n 1'th pipeline without using any extra variables and breaking pipeline?

For example, by using the code from Gregor Thomas,

mtcars %>%
  filter(mpg > 30) %T>%  #let this output to be y
  {\(x) (nrow(mtcars) - nrow(x)) %>% print}() %>% 
  filter(cyl  > 5)  %T>%
  {\(x) (nrow(y) - nrow(x)) %>% print}() 
#I know it is illegal to write 'y'

CodePudding user response：

I'd suggest using the magrittr %T>% "tee" pipe for the pass-through, with an anonymous function expression:

library(magrittr)

mtcars %>%
  filter(mpg > 30) %T>%
  {\(x) (nrow(mtcars) - nrow(x)) %>% print}()
# [1] 28
#                 mpg cyl disp  hp drat    wt  qsec vs am gear carb
# Fiat 128       32.4   4 78.7  66 4.08 2.200 19.47  1  1    4    1
# Honda Civic    30.4   4 75.7  52 4.93 1.615 18.52  1  1    4    2
# Toyota Corolla 33.9   4 71.1  65 4.22 1.835 19.90  1  1    4    1
# Lotus Europa   30.4   4 95.1 113 3.77 1.513 16.90  1  1    5    2

CodePudding user response：

You may change the function as following -

library(dplyr)

filter_pass_through <- function(data, ...) {
  res <- filter(data, ...)
  print(nrow(data) - nrow(res))
  res
}

mtcars %>% filter_pass_through(mpg>15) 

#[1] 6
#                   mpg cyl  disp  hp drat    wt  qsec vs am gear carb
#Mazda RX4         21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
#Mazda RX4 Wag     21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
#Datsun 710        22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1
#Hornet 4 Drive    21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1
#Hornet Sportabout 18.7   8 360.0 175 3.15 3.440 17.02  0  0    3    2
#Valiant           18.1   6 225.0 105 2.76 3.460 20.22  1  0    3    1
#...
#...