I have a set of objects that I read information out of that contain information that ends up becoming a MATLAB m file. One piece of information ends up being a function name in MATLAB. I need to remove all of the not-allowed characters from that string before writing the M file out to the filesystem. Can someone tell me what characters make up the set of allowed characters in a function name for MATLAB?
Legal names follow the pattern [A-Za-z][A-Za-z0-9_]*, i.e. an alphabetic character followed by zero or more alphanumeric-or-underscore characters, up to NAMELENGTHMAX characters.
Since MATLAB variable and function naming rules are the same, you might find genvarname useful. It sanitizes arbitrary strings into legal MATLAB names.
The short answer...
Any alphanumeric characters or underscores, as long as the name starts with a letter.
The longer answer...
The MATLAB documentation has a section "Working with M-Files" that discusses naming with a little more detail. Specifically, it points out the functions NAMELENGTHMAX (the maximum number of characters in the name that the OS will pay attention to), ISVARNAME (to check if the variable/function name is valid), and ISKEYWORD (to display restricted keywords).
Edited:
this may be more informative:
http://scv.bu.edu/documentation/tutorials/MATLAB/functions.html
Related
Let's say I was given random character reference like 〹. I need a solution to check whether this a valid encoding or not.
I think I can use the Charset lib but I can't fully wrap my mind on how to come up with a solution.
[This answer has been rewritten after further research.]
There's no simple answer to this using Charsets; see below for a complicated one.
There are simple answers using the character code, but it turns out to depend on exactly what you mean by ISO8859-1!
According to the Wikipedia page on ISO/IEC 8859-1, the character set ISO8859-1 defines only characters 32–126 and 160–255. So you could simply check for those ranges, e.g.:
fun Char.isISO8859_1() = this.toInt() in 32..126 || this.toInt() in 160..255
However, that same page also mentions the character set ISO-8859-1 (note the extra hyphen), which defines all 8-bit characters (0–255), assigning control characters to the extra ones. You could check for that with e.g.:
fun Char.isISO_8859_1() = this.toInt() in 0..255
ISO8859-1 includes all the printable characters, so if you only want to know whether a character has a defined glyph, you could use the former. However, these days most people tend to mean ISO-8859-1: that's what many web pages use (those which haven't yet moved on to UTF-8), and that's what the first 256 Unicode characters are defined as. So the latter will probably be more generally useful.
Both of the above methods are of course very short, simple, and efficient; but they only work for the one character set; and it's awkward hard-coding details of a character set, when library classes already have that information.
It seems that Charset objects are mainly aimed at encoding and decoding, so they don't provide a simple way to tell which characters are defined as such. But you can find out whether they can encode a given character. Here's the simplest way I found:
fun Char.isIn(charset: Charset) =
try {
charset.newEncoder()
.onUnmappableCharacter(CodingErrorAction.REPORT)
.encode(CharBuffer.wrap(toString()))
true
} catch (x: CharacterCodingException) {
false
}
That's really inefficient, but will work for all Charsets.
If you try this for ISO_8859_1, you'll find that it can encode all 8-bit values, i.e. 0–255. So it's clearly using the full ISO-8859-1 definition.
Going through the gensim source, I noticed the simple_preprocess utility function clears all punctuations except those with words starting with an underscore, _. Is there a reason for this?
def simple_preprocess(doc, deacc=False, min_len=2, max_len=15):
tokens = [
token for token in tokenize(doc, lower=True, deacc=deacc, errors='ignore')
if min_len <= len(token) <= max_len and not token.startswith('_')
]
return tokens
The underscore ('_') isn't typically meaningful punctuation, but is often considered a "word" character in programming and text-processing.
For example, common regular-expression syntax uses \w to indicate a "word character". Per https://www.regular-expressions.info/shorthand.html :
\w stands for "word character". It always matches the ASCII characters
[A-Za-z0-9_]. Notice the inclusion of the underscore and digits. In
most flavors that support Unicode, \w includes many characters from
other scripts. There is a lot of inconsistency about which characters
are actually included. Letters and digits from alphabetic scripts and
ideographs are generally included. Connector punctuation other than
the underscore and numeric symbols that aren't digits may or may not
be included. XML Schema and XPath even include all symbols in \w.
Again, Java, JavaScript, and PCRE match only ASCII characters with \w.
As such, it's often used in authoring, or in other text-preprocessing steps, to connect other groups of letters/numbers that should be kept together as a unit. Thus it's not often cleared with other true punctuation.
The code you've referenced also does something else, different than your question about clearing punctuation: it drops word-tokens beginning with _.
I'm not sure why it does that; at some point that code may have be designed with some specific text-format in mind where leading-underscore tokens were semantically-unimportant formatting directives.
The simple_preprocess() function in gensim is just a quick-and-dirty baseline helpful for internal tests and compact beginner tutorials. It shouldn't be considered a "best practice".
Real projects should give more consideration to the kind of word-tokenization that makes sense for their data and purposes – and either look to libraries with more options, or custom approaches (which still need not be more than a few lines of Python), to implement tokenization that best suits their needs.
I've tried the answers I've found in SOF, but none supported here : https://regexr.com
I essentially have an .OPML file with a large number of podcasts and descriptions.
in the following format:
<outline text="Software Engineering Daily" type="rss" xmlUrl="http://softwareengineeringdaily.com/feed/podcast/" htmlUrl="http://softwareengineeringdaily.com" />
What regex I can use to so I can just get the title and the link:
Software Engineering Daily
http://softwareengineeringdaily.com/feed/podcast/
Brief
There are many ways to go about this. The best way is likely using an XML parser. I would definitely read this post that discusses use of regex, especially with XML.
As you can see there are many answers to your question. It also depends on which language you are using since regex engines differ. Some accept backreferences, whilst others do not. I'll post multiple methods below that work in different circumstances/for different regex flavours. You can probably piece together from the multiple regex methods below which parts work best for you.
Code
Method 1
This method works in almost any regex flavour (at least the normal ones).
This method only checks against the attribute value opening and closing marks of " and doesn't include the possibility for whitespace before or after the = symbol. This is the simplest solution to get the values you want.
See regex in use here
\b(text|xmlUrl)="[^"]*"
Similarly, the following methods add more value to the above expression
\b(text|xmlUrl)\s*=\s*"[^"]*" Allows whitespace around =
\b(text|xmlUrl)=(?:"[^"]*"|'[^']*') Allows for ' to be used as attribute value delimiter
As another alternative (following the comments below my answer), if you wanted to grab every attribute except specific ones, you can use the following. Note that I use \w, which should cover most attributes, but you can just replace this with whatever valid characters you want. \S can be used to specify any non-whitespace characters or a set such as [\w-] may be used to specify any word or hyphen character. The negation of the specific attributes occurs with (?!text|xmlUrl), which says don't match those characters. Also, note that the word boundary \b at the beginning ensures that we're matching the full attribute name of text and not the possibility of other attributes with the same termination such as subtext.
\b((?!text|xmlUrl)\w+)="[^"]*"
Method 2
This method only works with regex flavours that allow backreferences. Apparently JGsoft applications, Delphi, Perl, Python, Ruby, PHP, R, Boost, and Tcl support single-digit backreferences. Double-digit backreferences are supported by JGsoft applications, Delphi, Python, and Boost. Information according this article about numbered backreferences from Regular-Expressions.info
See regex in use here
This method uses a backreference to ensure the same closing mark is used at the start and end of the attribute's value and also includes the possibility of whitespace surrounding the = symbol. This doesn't allow the possibility for attributes with no delimiter specified (using xmlUrl=http://softwareengineeringdaily.com/feed/podcast/ may also be valid).
See regex in use here
\b(text|xmlUrl)\s*=\s*(["'])(.*?)\2
Method 3
This method is the same as Method 2 but also allows attributes with no delimiters (note that delimiters are now considered to be space characters, thus, it will only match until the next space).
See regex in use here
\b(text|xmlUrl)\s*=\s*(?:(["'])(.*?)\2|(\S*))
Method 4
While Method 3 works, some people might complain that the attribute values might either of 2 groups. This can be fixed by either of the following methods.
Method 4.A
Branch reset groups are only possible in a few languages, notably JGsoft V2, PCRE 7.2+, PHP, Delphi, R (with PCRE enabled), Boost 1.42+ according to Regular-Expressions.info
This also shows the method you would use if backreferences aren't possible and you wanted to match multiple delimiters ("([^"])"|'([^']*))
See regex in use here
\b(text|xmlUrl)\s*=\s*(?|"([^"]*)"|'([^']*)'|(\S*))
Method 4.B
Duplicate subpatterns are not often supported. See this Regular-Expresions.info article for more information
This method uses the J regex flag, which allows duplicate subpattern names ((?<v>) is in there twice)
See regex in use here
\b(text|xmlUrl)\s*=\s*(?:(["'])(?<v>.*?)\2|(?<v>\S*))
Results
Input
<outline text="Software Engineering Daily" type="rss" xmlUrl="http://softwareengineeringdaily.com/feed/podcast/" htmlUrl="http://softwareengineeringdaily.com" />
Output
Each line below represents a different group. New matches are separated by two lines.
text
Software Engineering Daily
xmlUrl
http://softwareengineeringdaily.com/feed/podcast/
Explanation
I'll explain different parts of the regexes used in the Code section that way you understand the usage of each of these parts. This is more of a reference to the methods above.
"[^"]*" This is the fastest method possible (to the best of my knowledge) to grabbing anything between two " symbols. Note that it does not check for escaped backslashes, it will match any non-" character between two ". Whilst "(.*?)" can also be used, it's slightly slower
(["'])(.*?)\2 is basically shorthand for "(.*?)"|'(.*?)'. You can use any of the following methods to get the same result:
(?:"(.*?)"|'(.*?)')
(?:"([^"])"|'([^']*)') <-- slightly faster than line above
(?|) This is a branch reset group. When you place groups inside it like (?|(x)|(y)) it returns the same group index for both matches. This means that if x is captured, it'll get group index of 1, and if y is captured, it'll also get a group index of 1.
For simple HTML strings you might get along with
Url=(['"])(.+?)\1
Here, take group $2, see a demo on regex101.com.
Obligatory: consider using a parser instead (see here).
I came across this code written in TCL:
set GSID(featureSetDesc) #$GSID(descPath)/featDesc
But I can't seem to find what the "#" symbol stands for in TCL.. any help would be appreciated!
The commercial at symbol (#) doesn't mean anything special at all to Tcl. It's a normal non-letter non-whitespace character. (It does mean things to Tk in certain places such as when specifying a classic X11 bitmap that comes from a file for things like cursors or icons, but that's a pretty esoteric use these days.)
Well, there's one exception and that's channel redirections in exec. But that's not what you've got this case.
Assume the value of the variable GSID(descPath) equals "/home/me"
Then the value of GSID(featureSetDesc) will equal "#/home/me/featDesc"
What is the meaning of I $E(R%%,I%%)>1 ? and why using %%?
Actually, if you are talking about Standard MUMPS (not any particular implementation)
the R%% is illegal syntax. I have seen the non-standard use of % in extensions to MUMPS, such as EsiObjects or InterSystems Cache Object Script, but the use in the question above is actually nonsense in standard MUMPS.
There is no particular significance to %%. Its just part of the variable name and I still don't understand MUMPS community obsession with using % in variable names and making them more obscure.
so the statement means IF $EXTRACT(R%%,I%%)>1 i.e if the extracted value from the string R%% at position I%% is greater than 1, do some more obscure stuff.
$EXTRACT(string,from) extracts a
single character in the position
specified by from. The from value can
be an integer count from the beginning
of the string, an asterisk specifying
the last character of the string, or
an asterisk with a negative integer
specifying a count backwards from the
end of the string.
Link to documentation: http://docs.intersystems.com/cache20102/csp/docbook/DocBook.UI.Page.cls?KEY=RCOS_fextract