How to apply regexp before and after a certain character [duplicate] - javascript

This question already has answers here:
RegEx for a^b instead of pow(a,b)
(6 answers)
Closed 4 years ago.
I'd like to apply a regexp code to the part of a string that is before and/or after a specific character, and that character must be outside parenthesis.
To be more specific, I am coding a website (in React.JS) showing logical calculation, and I want to remove the first and last parenthesis before and after the main logical operator.
For example, in the string:
"((p∧r)∧(q∧r))∧(p∧q)"
I want to get only: "(p∧r)∧(q∧r)" and "p∧q".
That means I want to get all the character before and after the only "∧" outside of any parenthesis, and I want to remove the first opening parenthesis and the last closing parenthesis of the two string. (The result could be an array with the part before and after for example.)
I am already able to remove the first parenthis with this code :
str.replace(/(\()(.*)(\))/, "$2");
But that code is applied to the whole string right now.
So how do I apply this code to the two parts before and after the only "∧" outside parenthesis ? If possible I'd prefer a code only in regexp, but a JavaScript part would do. Thanks by advance.


You will not be able to do this in pure regex, this is similar of trying to parse HTML with regex. in short, it is not possible (and have been answered many time over in all possible way)
So you will need javascript. To do this in javascript will not be simple, as you will need to parse the entire string to find "^-who-are-not-in-parenthese".
I would first check if there is some parser for mathematical operation or other who already exist and could be adapted for your need.
If you do not find something, you will need to create yourself.
You could do it with a loop passing character by character, having a counter for the indentation level of parenthesis, and a tree-like data structure as an output.
you could also use regex to find the last level of indentation and creating a bottom-up parser. you find all the innerest parenthesis group, saved them, and replace them with a special identifier character. you can then redo the operation to find the now innerest parenthesis group, check if there is special character in them and place them in the tree (as parent of the element identified by the character.)
once you have your tree structure (in one way or another), the root and the first level of element should be what you want.


You could do it this way:
// your string
const fixMe = "((p∧r)∧(q∧r))^(p∧q)";
// Separate double paren items from single paren items
const parts = fixMe.match(/\(\(.*\)\)|\(.*\)/g).map(
// Get rid of leading and following parens
item => item.replace(/^\(|\)$/g, '')
);
However, note: this solution is not very flexible. Better might some sort of recursive parenthesis lookup where each loop keeps an accounting of nesting level, etc...

Related

Remove unquoted attribute from string [duplicate]

This question already has answers here:
Parse an HTML string with JS
(15 answers)
Closed 3 years ago.
I have an issue parsing the dom elements when text contains something like below. I wanted to remove highligted text from actual using Javascript. Can you please help me on this. I want to depend on regular expressions on the same.
I know how to get the quoted attributes using standard string functions and also using dom parser.
For the nodes like below, using string functions such as replace, slice may work but I need to traverse thru entire string. Which is performance issue.
So I wanted to go with regular expressions to find such attributes in a node.
<p class=MsoListParagraphCxSpFirst style='text-indent:-.25in;mso-list:l0 level1 lfo1'>
In the above example I want to remove class attribute and class name could be anything. These nodes are generated from MS word and are not in my control.
EDIT: Following is the pattern I am using to search unquoted text. But it is not working
var pattern = /<p class=\s*=\s*([^" >]+)/im

Regex101 Example
Regex:
\S+?=[^'"]\S*[^'"\s]
the tricky part with this one is finding the end of the unquoted attribute, in this example i'm assuming it will not contain any white space characters, so I can use the first occurrence of white space to terminate the match

JavaScript split string by specific character string

I have a text box with a bunch of comments, all separated by a specific character string as a means of splitting them to display each comment individually.
The string in question is | but I can change this to accommodate whatever will work. My only requirement is that it is not likely to be a string of characters someone will type in an everyday sentence.
I believe I need to use the split method and possibly some regex but all the other questions I've seen only seem to mention splitting by one character or a number of different characters, not a specific set of characters in a row.
Can anyone point me in the right direction?

.split() should work for that purpose:
var comments = "this is a comment|and here is another comment|and yet another one";
var parsedComments = comments.split('|');
This will give you all comments in an array which you can then loop over or do whatever you have to do.
Keep in mind you could also change | to something like <--NEWCOMMENT--> and it will still work fine inside the split('<--NEWCOMMENT-->') method.
Remember that split() removes the character it's splitting on, so your resulting array won't contain any instances of <--NEWCOMMENT-->

Match a word unless it is preceded by an equals sign?

I have the following string
class=use><em>use</em>
that when searched using us I want to transform into
class=use><em><b>us</b>e</em>
I've tried looking at relating answers but I can't quite get it working the way I want it to. I'm especially interested in this answer's callback approach.
Help appreciated

This is a good exercise for writing regular expressions, and here's a possible solution.
"useclass=use><em>use</em>".replace(/([^=]|^)(us)/g, "$1<b>$2</b>");
// returns "<b>us</b>eclass=use><em><b>us</b>e</em>"
([^=]|^) ensures that the prefix of any matched us is either not an equal sign, or it's the start of the string.
As #jamiec pointed out in the comments, if you are using this to parse/modify HTML, just stop right now. It's mathematically impossible to parse a CFG with a regular grammar (even with enhanced JS regexps you will have a bad time trying to achieve that.)

If you can make any assumptions about the structure of your document, you may be better off using an approach that operates on DOM elements directly rather than parsing the whole document with a regex.
Parsing HTML with a regex has certain problems that can be painful to deal with.
var element = document.querySelector('em');
element.innerHTML = element.innerHTML.replace('us', '<b>us</b>');
<div class=use><em>use</em>
</div>

I would first look for any character other than the equals sign [^=] and separate it by parentheses so that I can use it again in my replacement. Then another set of parentheses around the two characters us ought to do it:
var re = /([^=]|^)(us)/
That will give you two capture groups to work with (inside the parentheses), which you can represent with $1 and $2 in your replacement string.
str.replace( /([^=|^])(us)/, '$1<b>$2</b>' );

regex replace on JSON is removing an Object from Array

I'm trying to improve my understanding of Regex, but this one has me quite mystified.
I started with some text defined as:
var txt = "{\"columns\":[{\"text\":\"A\",\"value\":80},{\"text\":\"B\",\"renderer\":\"gbpFormat\",\"value\":80},{\"text\":\"C\",\"value\":80}]}";
and do a replace as follows:
txt.replace(/\"renderer\"\:(.*)(?:,)/g,"\"renderer\"\:gbpFormat\,");
which results in:
"{"columns":[{"text":"A","value":80},{"text":"B","renderer":gbpFormat,"value":80}]}"
What I expected was for the renderer attribute value to have it's quotes removed; which has happened, but also the C column is completely missing! I'd really love for someone to explain how my Regex has removed column C?
As an extra bonus, if you could explain how to remove the quotes around any value for renderer (i.e. so I don't have to hard-code the value gbpFormat in the regex) that'd be fantastic.

You are using a greedy operator while you need a lazy one. Change this:
"renderer":(.*)(?:,)
^---- add here the '?' to make it lazy
To
"renderer":(.*?)(?:,)
Working demo
Your code should be:
txt.replace(/\"renderer\"\:(.*?)(?:,)/g,"\"renderer\"\:gbpFormat\,");
If you are learning regex, take a look at this documentation to know more about greedyness. A nice extract to understand this is:
Watch Out for The Greediness!
Suppose you want to use a regex to match an HTML tag. You know that
the input will be a valid HTML file, so the regular expression does
not need to exclude any invalid use of sharp brackets. If it sits
between sharp brackets, it is an HTML tag.
Most people new to regular expressions will attempt to use <.+>. They
will be surprised when they test it on a string like This is a
first test. You might expect the regex to match and when
continuing after that match, .
But it does not. The regex will match first. Obviously not
what we wanted. The reason is that the plus is greedy. That is, the
plus causes the regex engine to repeat the preceding token as often as
possible. Only if that causes the entire regex to fail, will the regex
engine backtrack. That is, it will go back to the plus, make it give
up the last iteration, and proceed with the remainder of the regex.
Like the plus, the star and the repetition using curly braces are
greedy.

Try like this:
txt = txt.replace(/"renderer":"(.*?)"/g,'"renderer":$1');
The issue in the expression you were using was this part:
(.*)(?:,)
By default, the * quantifier is greedy by default, which means that it gobbles up as much as it can, so it will run up to the last comma in your string. The easiest solution would be to turn that in to a non-greedy quantifier, by adding a question mark after the asterisk and change that part of your expression to look like this
(.*?)(?:,)
For the solution I proposed at the top of this answer, I also removed the part matching the comma, because I think it's easier just to match everything between quotes. As for your bonus question, to replace the matched value instead of having to hardcode gbpFormat, I used a backreference ($1), which will insert the first matched group into the replacement string.

Don't manipulate JSON with regexp. It's too likely that you will break it, as you have found, and more importantly there's no need to.
In addition, once you have changed
'{"columns": [..."renderer": "gbpFormat", ...]}'
into
'{"columns": [..."renderer": gbpFormat, ...]}' // remove quotes from gbpFormat
then this is no longer valid JSON. (JSON requires that property values be numbers, quoted strings, objects, or arrays.) So you will not be able to parse it, or send it anywhere and have it interpreted correctly.
Therefore you should parse it to start with, then manipulate the resulting actual JS object:
var object = JSON.parse(txt);
object.columns.forEach(function(column) {
column.renderer = ghpFormat;
});
If you want to replace any quoted value of the renderer property with the value itself, then you could try
column.renderer = window[column.renderer];
Assuming that the value is available in the global namespace.
This question falls into the category of "I need a regexp, or I wrote one and it's not working, and I'm not really sure why it has to be a regexp, but I heard they can do all kinds of things, so that's just what I imagined I must need." People use regexps to try to do far too many complex matching, splitting, scanning, replacement, and validation tasks, including on complex languages such as HTML, or in this case JSON. There is almost always a better way.
The only time I can imagine wanting to manipulate JSON with regexps is if the JSON is broken somehow, perhaps due to a bug in server code, and it needs to be fixed up in order to be parseable.

Match attribute value of XML string in JS

I've researched stackoverflow and find similar results but it is not really what I wanted.
Given an xml string: "<a b=\"c\"></a>" in javascript context, I want to create a regex that will capture the attribute value including the quotation marks.
NOTE: this is similar if you're using single quotation marks.
Currently I have a regular expression tailored to the XML specification:
[_A-Za-z][\w\.\-]*(?:=\"[^\"]*\")?
[_A-Za-z][\w\.\-]* //This will match the attribute name.
(?:=\"[^\"]*\")? //This will match the attribute value.
\"[^\"]*\" //This part concerns me.
My question now is, what if the xml string looks like this:
<shout statement="Hi! \"Richeve\"."></shout>
I know this is a dumb question to ask but I just want to capture rare cases that this scenario might happen (I know the coder can use single quotes on this scenario) but there are cases that we don't know the current value of the attribute given that the attribute value changes dynamically at runtime.
So to make this clearer, the result of that using the correct regex should be:
"Hi! \"Richeve\"."
I hope my question is clear. Thanks for all the help!
PS: Note that the language context is Javascript and I know it is tempting to use lookbehinds but currently lookbehinds are not supported.
PS: I know it is really hard to parse XML but I have an elegant solution to this :) so I just need this small problem to be solved. So this problem only main focus is capturing quotation marked string tokens containing quotation marks inside the string token.

The standard pattern for content with matching delimiters and embedded escaped delimiters goes like this:
"[^"\\]*(?:\\.[^"\\]*)*"
Ignoring the obvious first and last characters in the pattern, here's how the rest of the pattern works:
[^"\\]*: Consume all characters until a delimiter OR backslash (matching Hi! in your example)
(?:\\.[^"\\]*)* Try to consume a single escaped character \\. followed by a series of non delimiter/backslash characters, repeatedly (matching \"Richeve first and then \". next in your example)
That's it.
You can try to use a more generic delimiter approach using (['"]) and back references, or you can just allow for an alternate pattern with single quotes like so:
("[^"\\]*(?:\\.[^"\\]*)*"|'[^'\\]*(?:\\.[^'\\]*)*')
Here's another description of this technique that might also help (see the section called Strings): http://www.regular-expressions.info/examplesprogrammer.html

Description
I'm pretty really sure embedding double quotes inside a double quoted attribute value is not legal. You could use the unicode equivalent of a double quote \x22 inside the value.
However to answer the question, this expression will:
allow escaped quotes inside attribute values
capture the attribute statement 's value
allow attributes to appear in any order inside the tag
will avoid many of the edge cases which will trip up pattern matching inside html text
doesn't use lookbehinds
<shout\b(?=\s)(?=(?:[^>=]|='(?:[^']|\\')*'|="(?:[^"]|\\")*"|=[^'"][^\s>]*)*?\sstatement=(['"])((?:\\['"]|.)*?)\1(?:\s|\/>|>))(?:[^>=]|='(?:[^']|\\')*'|="(?:[^"]|\\")*"|=[^'"][^\s>]*)*>.*?<\/shout>
Example
Pretty Rubular
Ugly RegexPlanet set to Javascript
Sample Text
Note the difficult edge case in the first attribute :)
<shout onmouseover=' statement="He said \"I am Inside the onMouseOver\" " ; if ( 6 > a ) { funRotate(statement) } ; ' statement="Hi! \"Richeve\"." title="sometitle">SomeString</shout>
Matches
Group 0 gets the entire tag from open to close
Group 1 gets the quote surrounding the statement attribute value, this is used to match the closing quote correctly
Group 2 gets the statement attribute value which may include escaped quotes like \" but not including the surrounding quotes
[0][0] = <shout onmouseover=' statement="He said \"I am Inside the onMouseOver\" " ; if ( 6 > a ) { funRotate(statement) } ; ' statement="Hi! \"Richeve\"." title="sometitle">SomeString</shout>
[0][1] = "
[0][2] = Hi! \"Richeve\".

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