Most everybody on this list probably understands the power of regexp's for
string processing. Has anybody ever given thought to creating a vector
regexp (I would call it 'subsetting') for codifying complex slices?
Here's what I've come up with so far:
Basic Metacharacters
====================
^ Match the beginning of a vector
$ Match the end of a vector
| Alternation
() Grouping
. Match a single number
Numerical Ranges
================
(a,b) match any number c such that a < c < b
(a,b] match any number c such that a < c <= b
[a,b) match any number c such that a <= c < b
[a,b] match any number c such that a <= c <= b
Quantifiers
===========
* Match 0 or more times
+ Match 1 or more times
? Match 1 or 0 times
{n} Match exactly n times
{n,} Match at least n times
{n,m} Match at least n but not more than m times
Slicing
=======
s() Include this group in the resulting slice.
Metacharacters
==============
p matches a positive number
P matches a positive number or zero
n matches a negative number
N matches a negative number or zero
o matches zero
O matches nonzero
M matches a local maximum
N matches any character that is not a local maximum
m mathces a local minimum
n matches any character that is not a local minimum
M{n} matches a local maximum near index n
m{n} mathces a local minimum near index n
\M matches the global maximum
\m matches the global minimum
Zero-width Assertions
=====================
\c Match a zero crossing
\c+ Match a positively sloped zero crossing
\c- Match a negatively sloped zero crossing
\c=a Match when the time-series crosses the value a
\c=a+ Match when the time-series crosses the value a with positive slope
\c=a+ Match when the time-series crosses the value a with negative slope
\dN Match where the Nth numerical derivative crosses zero (also for +- and
=)
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