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Compare - Pattern matching

match_hash.Rd

Pattern matching functions to return a value based on a case of x. Similar to switch() but allows for any type for object as the case. Cases are two sided formulas with the LHS being the case and the RHS being the return value.

  • For match_hash and match_id, cases are any R object to directly compare with x.

  • For match_ptype, cases are prototypes to check if x is_ptype().

  • For match_when, cases are any predicate expression, that matches when it evaluates to TRUE.

Usage

match_hash(x, ..., nomatch = NULL, htab = NULL, type = NULL, size = NULL)

match_id(x, ..., nomatch = NULL, fun = "identical", args_id = list())

match_ptype(x, ..., nomatch = NULL, args_ptype = list())

match_when(x, ..., nomatch = NULL)

Arguments

x

[any] Object to match.

...

[<formula> each] Cases to match. Each case is a formula with the left-hand side being the value to match against and the right-hand side being the value to return if the case matches. Cases are evaluated in order, and in the caller environment.

nomatch

[any] Value to return if no cases match. Use stop() or similar to err.

htab, type, size

[hashtab() | NULL, character(1) | NULL, integer(1) | NULL] For match_hash: an existing hash table, or the arguments passed to utils::hashtab() to create a new one.

fun, args_id

[character(1), list()] For match_id: which 'identical' function to use, "identical" for identical() or "identical2" for identical2(); and a list of arguments to pass to it.

args_ptype

[list()] For match_ptype. A list of arguments to pass to is_ptype().

Value

[any] The value of the first matching case, or nomatch if no cases match.

Details

The return value is evaluated dynamically and can refer to x, except for match_hash, which in turn is faster and can be supplied a pre-built hash table.

Examples

match_hash(1.42, 1.42 ~ base::sum, "oi" ~ -Inf) #> base::sum
#> function (..., na.rm = FALSE)  .Primitive("sum")

# The htab can be reused to speed up repeated calls to match_hash():
htab <- utils::hashtab(size = 2)
utils::sethash(htab, 1.42, base::sum)
utils::sethash(htab, "oi", -Inf)
match_hash(1.42, htab = htab) #> base::sum
#> function (..., na.rm = FALSE)  .Primitive("sum")

match_id(1.42, "oi" ~ -Inf, 1.42 ~ .x * 2) #> 2.84
#> [1] 2.84

match_ptype(1.42, character() ~ "chr", double() ~ "dbl") #> "dbl"
#> [1] "dbl"

match_when("oi", grepl("1", .x) ~ "1", grepl("o", .x) ~ "o") #> "o"
#> [1] "o"