[R] Regexp bug or misunderstanding
toth@dene@ @end|ng |rom kogentum@hu
Mon Jul 2 15:03:47 CEST 2018
I assume you want to check whether a particular character string
contains a digit. In this case you should use the following pattern:
"[[:digit:]]" instead of "[:digit:]".
"A character class is a list of characters enclosed between [ and ]
which matches any single character in that list; unless the first
character of the list is the caret ^, when it matches any character not
in the list. ... Certain named classes of characters are predefined...
For example, [[:alnum:]] means [0-9A-Za-z]"
So if you use simply "[:digit:]" as a pattern, it means: a character
string which contains any of the following characters: ':', 'd', 'i',
'g', 't'. Your second test case contains 'd', whereas the first case
contains neither of the above characters.
On 07/02/2018 02:52 PM, Martin Møller Skarbiniks Pedersen wrote:
> Have I found a bug in R? Or misunderstood something about grep() ?
> Case 1 gives the expected output
> Case 2 does not gives the expected output.
> I expected integer(0) also for this case.
> case 1:
> grep("[:digit:]", "**ABAAbabaabackabaloneaban")
> case 2:
> grep("[:digit:]", "**ABAAbabaabackabaloneaband")
>  1
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