Any way in R to keep only columns whose rows are filtered?-CodePudding

In dplyr I see an argument in the mutate function which is .keep. It takes the values "all", "used", "unused", or "none". Where if I pass "used", only the calculated columns and the used columns are shown.

library(dplyr)
df <- tibble(x = c(1,2,3), 
             y = c(2,1,4),
             a = 10:12,
             b = 12:10)
df %>% mutate(z = x   y, .keep = "used")

Output:

x y z
1 2 3
2 1 3
3 4 7

Here the columns a and b are not shown.
My question: Is there any way to do the same thing when I filter some columns? I want only the columns where the filter operation is performed on the rows based on some condition.

CodePudding user response：

Let's say you are applying this filter on your dataset.

library(dplyr)
mtcars %>% filter(cyl > 4 & mpg < 15)

#                     mpg cyl disp  hp drat    wt  qsec vs am gear carb
#Duster 360          14.3   8  360 245 3.21 3.570 15.84  0  0    3    4
#Cadillac Fleetwood  10.4   8  472 205 2.93 5.250 17.98  0  0    3    4
#Lincoln Continental 10.4   8  460 215 3.00 5.424 17.82  0  0    3    4
#Chrysler Imperial   14.7   8  440 230 3.23 5.345 17.42  0  0    3    4
#Camaro Z28          13.3   8  350 245 3.73 3.840 15.41  0  0    3    4

You may save the query in a variable using mutate to make use of .keep argument and then filter it with the condition. Finally, drop the condition column from the output.

mtcars %>% 
  mutate(result = cyl > 4 & mpg < 15, .keep = "used") %>%
  filter(result) %>%
  select(-result)

#                     mpg cyl
#Duster 360          14.3   8
#Cadillac Fleetwood  10.4   8
#Lincoln Continental 10.4   8
#Chrysler Imperial   14.7   8
#Camaro Z28          13.3   8