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# stri_enc_detect: Detect Character Set and Language

## Description

This function uses the ICU engine to determine the character set, or encoding, of character data in an unknown format.

## Usage

    stri_enc_detect(str, filter_angle_brackets = FALSE)

## Arguments

`str` | character vector, a raw vector, or a list of `raw` vectors
`filter_angle_brackets` | logical; If filtering is enabled, text within angle brackets (‘<’ and ‘>’) will be removed before detection, which will remove most HTML or XML markup.

## Details

Vectorized over `str` and `filter_angle_brackets`.

For a character vector input, merging all text lines via `stri_flatten(str, collapse='\n')` might be needed if `str` has been obtained via a call to `readLines` and in fact represents an image of a single text file.

This is, at best, an imprecise operation using statistics and heuristics. Because of this, detection works best if you supply at least a few hundred bytes of character data that is mostly in a single language. However, because the detection only looks at a limited amount of the input data, some of the returned character sets may fail to handle all of the input data. Note that in some cases, the language can be determined along with the encoding.

Several different techniques are used for character set detection. For multi-byte encodings, the sequence of bytes is checked for legible patterns. The detected characters are also checked against a list of frequently used characters in that encoding. For single byte encodings, the data is checked against a list of the most commonly occurring three letter groups for each language that can be written using that encoding.

The detection process can be configured to optionally ignore HTML or XML style markup (using ICU’s internal facilities), which can interfere with the detection process by changing the statistics.

This function should most often be used for byte-marked input strings, especially after loading them from text files and before the main conversion with `stri_encode`. The input encoding is of course not taken into account here, even if marked.

The following table shows all the encodings that can be detected:

Character_Set | Languages
UTF-8 | –
UTF-16BE | –
UTF-16LE | –
UTF-32BE | –
UTF-32LE | –
Shift_JIS | Japanese
ISO-2022-JP | Japanese
ISO-2022-CN | Simplified Chinese
ISO-2022-KR | Korean
GB18030 | Chinese
Big5 | Traditional Chinese
EUC-JP | Japanese
EUC-KR | Korean
ISO-8859-1 | Danish, Dutch, English, French, German, Italian, Norwegian, Portuguese, Swedish
ISO-8859-2 | Czech, Hungarian, Polish, Romanian
ISO-8859-5 | Russian
ISO-8859-6 | Arabic
ISO-8859-7 | Greek
ISO-8859-8 | Hebrew
ISO-8859-9 | Turkish
windows-1250 | Czech, Hungarian, Polish, Romanian
windows-1251 | Russian
windows-1252 | Danish, Dutch, English, French, German, Italian, Norwegian, Portuguese, Swedish
windows-1253 | Greek
windows-1254 | Turkish
windows-1255 | Hebrew
windows-1256 | Arabic
KOI8-R | Russian
IBM420 | Arabic
IBM424 | Hebrew

## Value

Returns a list of length equal to the length of `str`. Each list element is a data frame with the following three named vectors representing all the guesses:

- `Encoding` – string; guessed encodings; `NA` on failure,

- `Language` – string; guessed languages; `NA` if the language could not be determined (e.g., in case of UTF-8),

- `Confidence` – numeric in [0,1]; the higher the value, the more confidence there is in the match; `NA` on failure.

The guesses are ordered by decreasing confidence.

## Author(s)

Marek Gagolewski and other contributors

## References

Character Set Detection – ICU User Guide, https://unicode-org.github.io/icu/userguide/conversion/detection.html

## 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 encoding_detection: `about_encoding`, `stri_enc_detect2()`, `stri_enc_isascii()`, `stri_enc_isutf16be()`, `stri_enc_isutf8()`

## Examples

    ## Not run:
    ## f <- rawToChar(readBin('test.txt', 'raw', 100000))
    ## stri_enc_detect(f)