Extract Positions of Unique Elements

unipos returns the positions of those elements returned by unique().

Usage

unipos(x, incomparables = FALSE, order = c("original", "values", "any"), ...)

# S3 method for class 'integer64'
unipos(
  x,
  incomparables = FALSE,
  order = c("original", "values", "any"),
  nunique = NULL,
  method = NULL,
  ...
)

Arguments

x: a vector or a data frame or an array or NULL.
incomparables: ignored
order: The order in which positions of unique values will be returned, see details
...: ignored
nunique: NULL or the number of unique values (including NA). Providing nunique can speed-up when x has no cache. Note that a wrong nunique can cause undefined behaviour up to a crash.
method: NULL for automatic method selection or a suitable low-level method, see details

Value

an integer vector of positions

Details

This function automatically chooses from several low-level functions considering the size of x and the availability of a cache.

Suitable methods are

hashmapupo (simultaneously creating and using a hashmap)
hashupo (first creating a hashmap then using it)
sortorderupo (fast ordering)
orderupo (memory saving ordering).

The default order="original" collects unique values in the order of the first appearance in x like in unique(), this costs extra processing. order="values" collects unique values in sorted order like in table(), this costs extra processing with the hash methods but comes for free. order="any" collects unique values in undefined order, possibly faster. For hash methods this will be a quasi random order, for sort methods this will be sorted order.

Examples

x <- as.integer64(sample(c(rep(NA, 9), 1:9), 32, TRUE))
unipos(x)
#> [1]  1  2  3  4  5  8 14 25
unipos(x, order="values")
#> [1]  3  5  4 14  2  1 25  8

stopifnot(identical(unipos(x),  (1:length(x))[!duplicated(x)]))
stopifnot(identical(unipos(x),  match.integer64(unique(x), x)))
stopifnot(identical(unipos(x, order="values"),  match.integer64(unique(x, order="values"), x)))
stopifnot(identical(unique(x),  x[unipos(x)]))
stopifnot(identical(unique(x, order="values"),  x[unipos(x, order="values")]))