7.11 Other predicates

keep, discard

only keeps or discards TRUE values

iris %>% 
  keep(is.factor) %>% 
  str()
## 'data.frame':    150 obs. of  1 variable:
##  $ Species: Factor w/ 3 levels "setosa","versicolor",..: 1 1 1 1 1 1 1 1 1 1 ...

some and every work like any and all

x <- list(1:5, letters, list(10))

x %>% 
  some(is_character)
## [1] TRUE

detect and detect_index finds the first element

x <- sample(10)
x
##  [1]  2  8  7  3  5  6  4  1 10  9

x %>% 
  detect(~ . > 5)
## [1] 8

head_while tail_while returns the head or tail while something is true

x
##  [1]  2  8  7  3  5  6  4  1 10  9

x %>% 
  head_while(~ . > 5)
## integer(0)

x %>% 
  tail_while(~ . > 5)
## [1] 10  9

reduce applies a function until there is only one left. Useful for repeadily joinging dataframes together

dfs <- list(
  age = tibble(name = "John", age = 30),
  sex = tibble(name = c("John", "Mary"), sex = c("M", "F")),
  trt = tibble(name = "Mary", treatment = "A")
)

dfs
## $age
## # A tibble: 1 x 2
##   name    age
##   <chr> <dbl>
## 1 John     30
## 
## $sex
## # A tibble: 2 x 2
##   name  sex  
##   <chr> <chr>
## 1 John  M    
## 2 Mary  F    
## 
## $trt
## # A tibble: 1 x 2
##   name  treatment
##   <chr> <chr>    
## 1 Mary  A

dfs %>% reduce(full_join)
## Joining, by = "name"
## Joining, by = "name"
## # A tibble: 2 x 4
##   name    age sex   treatment
##   <chr> <dbl> <chr> <chr>    
## 1 John     30 M     <NA>     
## 2 Mary     NA F     A