# 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

``` r
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 <span class="pkg">ICU</span> Collator\'s options, see [`stri_opts_collator`](stri_opts_collator.md), `NULL` for default collation options |

## Details

Missing values are regarded as equal.

Unlike [`duplicated`](https://stat.ethz.ch/R-manual/R-devel/library/base/html/duplicated.html) and [`anyDuplicated`](https://stat.ethz.ch/R-manual/R-devel/library/base/html/duplicated.html), 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`](stri_unique.md) 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](https://www.gagolewski.com/) and other contributors

## References

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

## See Also

The official online manual of <span class="pkg">stringi</span> at <https://stringi.gagolewski.com/>

Gagolewski M., <span class="pkg">stringi</span>: Fast and portable character string processing in R, *Journal of Statistical Software* 103(2), 2022, 1-59, [doi:10.18637/jss.v103.i02](https://doi.org/10.18637/jss.v103.i02)

Other locale_sensitive: [`%s<%()`](+25s+3C+25.md), [`about_locale`](about_locale.md), [`about_search_boundaries`](about_search_boundaries.md), [`about_search_coll`](about_search_coll.md), [`stri_compare()`](stri_compare.md), [`stri_count_boundaries()`](stri_count_boundaries.md), [`stri_enc_detect2()`](stri_enc_detect2.md), [`stri_extract_all_boundaries()`](stri_extract_boundaries.md), [`stri_locate_all_boundaries()`](stri_locate_boundaries.md), [`stri_opts_collator()`](stri_opts_collator.md), [`stri_order()`](stri_order.md), [`stri_rank()`](stri_rank.md), [`stri_sort()`](stri_sort.md), [`stri_sort_key()`](stri_sort_key.md), [`stri_split_boundaries()`](stri_split_boundaries.md), [`stri_trans_tolower()`](stri_trans_casemap.md), [`stri_unique()`](stri_unique.md), [`stri_wrap()`](stri_wrap.md)

## Examples




``` r
# 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
```

``` r
stri_duplicated(c('a', 'b', 'a', NA, 'a', NA), from_last=TRUE)
```

```
## [1]  TRUE FALSE  TRUE  TRUE FALSE FALSE
```

``` r
stri_duplicated_any(c('a', 'b', 'a', NA, 'a', NA))
```

```
## [1] 3
```

``` r
# compare the results:
stri_duplicated(c('\u0105', stri_trans_nfkd('\u0105')))
```

```
## [1] FALSE  TRUE
```

``` r
duplicated(c('\u0105', stri_trans_nfkd('\u0105')))
```

```
## [1] FALSE FALSE
```

``` r
stri_duplicated(c('gro\u00df', 'GROSS', 'Gro\u00df', 'Gross'), strength=1)
```

```
## [1] FALSE  TRUE  TRUE  TRUE
```

``` r
duplicated(c('gro\u00df', 'GROSS', 'Gro\u00df', 'Gross'))
```

```
## [1] FALSE FALSE FALSE FALSE
```
