7.3 Predicate functions

7.3.1 Basics

df <- data.frame(x = 1:3, y = c("a", "b", "c"))

df %>% 
  keep(is.numeric)
#>   x
#> 1 1
#> 2 2
#> 3 3

df %>% 
  discard(is.numeric)
#>   y
#> 1 a
#> 2 b
#> 3 c

df %>% 
  mutate(new_col = LETTERS[1:3]) %>%
  detect(is.factor)
#> [1] a b c
#> Levels: a b c

df %>% 
  detect_index(is.factor)
#> [1] 2

7.3.2 Map variants

df <- data.frame(
  num1 = c(0, 10, 20),
  num2 = c(5, 6, 7),
  chr1 = c("a", "b", "c"),
  stringsAsFactors = FALSE
)


df %>% 
  map_if(is.numeric, mean, na.rm = T) %>% 
  str()
#> List of 3
#>  $ num1: num 10
#>  $ num2: num 6
#>  $ chr1: chr [1:3] "a" "b" "c"

df %>% 
  modify_if(is.character, str_to_upper) %>% 
  str()
#> 'data.frame':    3 obs. of  3 variables:
#>  $ num1: num  0 10 20
#>  $ num2: num  5 6 7
#>  $ chr1: chr  "A" "B" "C"