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# stri_duplicated: Determine Duplicated Elements

## Description

`stri_duplicated()` determines which strings in a character vector are duplicates of other elements.

`stri_duplicated_any()` determines if there are any duplicated strings in a character vector.

## Usage

    stri_duplicated(
      str,
      from_last = FALSE,
      fromLast = from_last,
      ...,
      opts_collator = NULL
    )

    stri_duplicated_any(
      str,
      from_last = FALSE,
      fromLast = from_last,
      ...,
      opts_collator = NULL
    )

## Arguments

`str` | a character vector
`from_last` | a single logical value; indicates whether search should be performed from the last to the first string
`fromLast` | [DEPRECATED] alias of `from_last`
`...` | additional settings for `opts_collator`
`opts_collator` | a named list with ICU Collator’s options, see `stri_opts_collator`, `NULL` for default collation options

## Details

Missing values are regarded as equal.

Unlike `duplicated` and `anyDuplicated`, these functions test for canonical equivalence of strings (and not whether the strings are just bytewise equal) Such operations are locale-dependent. Hence, `stri_duplicated` and `stri_duplicated_any` are significantly slower (but much better suited for natural language processing) than their base R counterparts.

See also `stri_unique` for extracting unique elements.

## Value

`stri_duplicated()` returns a logical vector of the same length as `str`. Each of its elements indicates whether a canonically equivalent string was already found in `str`.

`stri_duplicated_any()` returns a single non-negative integer. Value of 0 indicates that all the elements in `str` are unique. Otherwise, it gives the index of the first non-unique element.

## Author(s)

Marek Gagolewski and other contributors

## References

Collation - ICU User Guide, https://unicode-org.github.io/icu/userguide/collation/

## See Also

The official online manual of stringi at https://stringi.gagolewski.com/

Gagolewski M., stringi: Fast and portable character string processing in R, Journal of Statistical Software 103(2), 2022, 1-59, doi:10.18637/jss.v103.i02

Other locale_sensitive: `%s<%()`, `about_locale`, `about_search_boundaries`, `about_search_coll`, `stri_compare()`, `stri_count_boundaries()`, `stri_enc_detect2()`, `stri_extract_all_boundaries()`, `stri_locate_all_boundaries()`, `stri_opts_collator()`, `stri_order()`, `stri_rank()`, `stri_sort()`, `stri_sort_key()`, `stri_split_boundaries()`, `stri_trans_tolower()`, `stri_unique()`, `stri_wrap()`

## Examples

    # In the following examples, we have 3 duplicated values,
    # 'a' - 2 times, NA - 1 time
    stri_duplicated(c('a', 'b', 'a', NA, 'a', NA))
    ## [1] FALSE FALSE  TRUE FALSE  TRUE  TRUE
    stri_duplicated(c('a', 'b', 'a', NA, 'a', NA), from_last=TRUE)
    ## [1]  TRUE FALSE  TRUE  TRUE FALSE FALSE
    stri_duplicated_any(c('a', 'b', 'a', NA, 'a', NA))
    ## [1] 3
    # compare the results:
    stri_duplicated(c('\u0105', stri_trans_nfkd('\u0105')))
    ## [1] FALSE  TRUE
    duplicated(c('\u0105', stri_trans_nfkd('\u0105')))
    ## [1] FALSE FALSE
    stri_duplicated(c('gro\u00df', 'GROSS', 'Gro\u00df', 'Gross'), strength=1)
    ## [1] FALSE  TRUE  TRUE  TRUE
    duplicated(c('gro\u00df', 'GROSS', 'Gro\u00df', 'Gross'))
    ## [1] FALSE FALSE FALSE FALSE