Regular expressions {GCDkit} | R Documentation |
Implementation of regular expressions in the searching patterns.
Many enquiries in the GCDkit employ regular expressions. This is a quite powerful searching mechanism more familiar to people working in Unix. Put in simple terms, most characters, including all letters and digits, are regular expressions that match themselves. However, metacharacters with a special meaning ('?' '+' '{' '}' '|' '(' ')') must be preceded by a backslash.
Regular expression | Matches |
. | Any character |
^ | Beginning of the expression |
\$ | End of the expression |
[ ] | Any of the characters given in square brackets |
[m-n] | Any character in the range given by m and n |
A subexpression is a regular expression enclosed in '\(' and '\)'. Two such subexpressions may be joined by the infix operator '|' (logical or); the resulting regular expression matches any string matching either of them. For instance:
\(South\)|\(North\)Uist
yields both
South Uist
and North Uist
.
A regular expression may be followed by one of several repetition operators:
Repetition operator | The preceding item will be matched |
? | At most once (i.e. is optional) |
* | Zero or more times |
+ | One or more times |
{n} | Exactly n times |
{n,} | At least n times |
{n,m} | At least n times, but not more than m times |
Vojtech Janousek, vojtech.janousek@geology.cz
## Not run: # Subset by label The searched field corresponds to localities with the following levels: Mull, Rum, Skye, Coll, Colonsay, Hoy, Westray, Sanday, Stronsay, Tiree, Islay Search pattern = ol Coll, Colonsay Search pattern = n.a Colonsay, Sanday, Stronsay Search pattern = ^S Skye, Sanday, Stronsay Search pattern = e$ Skye, Tiree Search pattern = [ds]ay Colonsay, Sanday, Stronsay Search pattern = [p-s]ay Colonsay, Westray, Stronsay Search pattern = ol|oy Coll, Colonsay, Hoy Search pattern = l{2} Mull, Coll # Subset by sample name The sample names are: Bl-1, Bl-3, Koz-1, Koz-2, Koz-5, Koz-11, KozD-1, Ri-1. Search pattern = oz-[1-3] Koz-1, Koz-2, Koz-11 Search pattern = oz-|Bl- Bl-1, Bl-2, Bl-3, Koz-1, Koz-2, Koz-5, Koz-11 ## End(Not run)