R readr parse_factor 解析因子

parse_factor(
  x,
  levels = NULL,
  ordered = FALSE,
  na = c("", "NA"),
  locale = default_locale(),
  include_na = TRUE,
  trim_ws = TRUE
)

col_factor(levels = NULL, ordered = FALSE, include_na = FALSE)

其他解析器：col_skip() , cols_condense() , cols() , parse_datetime() , parse_guess() , parse_logical() , parse_number() , parse_vector()

# discover the levels from the data
parse_factor(c("a", "b"))
#> [1] a b
#> Levels: a b
parse_factor(c("a", "b", "-99"))
#> [1] a   b   -99
#> Levels: a b -99
parse_factor(c("a", "b", "-99"), na = c("", "NA", "-99"))
#> [1] a    b    <NA>
#> Levels: a b <NA>
parse_factor(c("a", "b", "-99"), na = c("", "NA", "-99"), include_na = FALSE)
#> [1] a    b    <NA>
#> Levels: a b

# provide the levels explicitly
parse_factor(c("a", "b"), levels = letters[1:5])
#> [1] a b
#> Levels: a b c d e

x <- c("cat", "dog", "caw")
animals <- c("cat", "dog", "cow")

# base::factor() silently converts elements that do not match any levels to
# NA
factor(x, levels = animals)
#> [1] cat  dog  <NA>
#> Levels: cat dog cow

# parse_factor() generates same factor as base::factor() but throws a warning
# and reports problems
parse_factor(x, levels = animals)
#> Warning: 1 parsing failure.
#> row col           expected actual
#>   3  -- value in level set    caw
#> [1] cat  dog  <NA>
#> attr(,"problems")
#> # A tibble: 1 × 4
#>     row   col expected           actual
#>   <int> <int> <chr>              <chr> 
#> 1     3    NA value in level set caw   
#> Levels: cat dog cow