I'm parsing a txt file (an old hymns book). I want to do the following:
Get the chorus
Parse/santize each line of that chorus
I've tried this code:
chorus_regex = /([^0-9]+\n)+/
puts hymn.gsub(chorus_regex) {|match| match.gsub(/^([^0-9]+\n)/, " \1")}
But the second gsub is only affecting the first line? I think it's because the \1 might be applied to the first regex, not the second
TL;DR
How do you write nested gsubs, so that you can grab blocks of txt, do a gsub on those blocks, and replace the old blocks with the results?
Edit
I simplified the regexes, so the question is focused on how to nest regex gsubs, and not distracted by complicated regex or badly encoded chars.
To nest gsubs, make sure you use blocks for the gsubs, and you can use the perlisms ($1 for first group, etc).
chorus_regex = /([^0-9]+\n)+/
puts hymn.gsub(chorus_regex) {|match|
match.gsub(/^([^0-9]+\n)/) { |line|
" #{$1}"
}
}
Related
Lets say I have the following string and I want the below output without requiring csv.
this, "what I need", to, do, "i, want, this", to, work
this
what i need
to
do
i, want, this
to
work
This problem is a classic case of the technique explained in this question to "regex-match a pattern, excluding..."
We can solve it with a beautifully-simple regex:
"([^"]+)"|[^, ]+
The left side of the alternation | matches complete "quotes" and captures the contents to Group1. The right side matches characters that are neither commas nor spaces, and we know they are the right ones because they were not matched by the expression on the left.
Option 2: Allowing Multiple Words
In your input, all tokens are single words, but if you also want the regex to work for my cat scratches, "what I need", your dog barks, use this:
"([^"]+)"|[^, ]+(?:[ ]*[^, ]+)*
The only difference is the addition of (?:[ ]*[^, ]+)* which optionally adds spaces + characters, zero or more times.
This program shows how to use the regex (see the results at the bottom of the online demo):
subject = 'this, "what I need", to, do, "i, want, this", to, work'
regex = /"([^"]+)"|[^, ]+/
# put Group 1 captures in an array
mymatches = []
subject.scan(regex) {|m|
$1.nil? ? mymatches << $& : mymatches << $1
}
mymatches.each { |x| puts x }
Output
this
what I need
to
do
i, want, this
to
work
Reference
How to match (or replace) a pattern except in situations s1, s2, s3...
Article about matching a pattern unless...
Here's my regular expression that I have for this. I'm in Ruby, which — if I'm not mistaken — uses POSIX regular expressions.
regex = /(?:\n^)(\*[\w+ ?]+\*)\n/
Here's my goal: I want to split a string with a regex that is *delimited by asterisks*, including those asterisks. However: I only want to split by the match if it is prefaced with a newline character (\n), or it's the start of the whole string. This is the string I'm working with.
"*Friday*\nDo not *break here*\n*But break here*\nBut again, not this"
My regular expression is not splitting properly at the *Friday* match, but it is splitting at the *But break here* match (it's also throwing in a here split). My issue is somewhere in the first group, I think: (?:\n^) — I know it's wrong, and I'm not entirely sure of the correct way to write it. Can someone shed some light? Here's my complete code.
regex = /(?:\n^)(\*[\w+ ?]+\*)\n/
str = "*Friday*\nDo not *break here*\n*But break here*\nBut again, not this"
str.split(regex)
Which results in this:
>>> ["*Friday*\nDo not *break here*", "*But break here*", "But again, not this"]
I want it to be this:
>>> ["*Friday*", "Do not *break here*", "*But break here*", "But again, not this"]
Edit #1: I've updated my regex and result. (2011/10/18 16:26 CST)
Edit #2: I've updated both again. (16:32 CST)
What if you just add a '\n' to the front of each string. That simplifies the processing quite a bit:
regex = /(?:\n)(\*[\w+ ?]+\*)\n/
str = "*Friday*\nDo not *break here*\n*But break here*\nBut again, not this"
res = ("\n"+str).split(regex)
res.shift if res[0] == ""
res
=> [ "*Friday*", "Do not *break here*",
"*But break here*", "But again, not this"]
We have to watch for the initial extra match but it's not too bad. I suspect someone can shorten this a bit.
Groups 1 & 2 of the regex below :
(?:\A|\\n)(\*.*?\*)|(?:\A|\\n)(.*?)(?=\\n|\Z)
Will give you your desired output. I am no ruby expert so you will have to create the list yourself :)
Why not just split at newlines? From your example, it looks that's what you're really trying to do.
str.split("\n")
I have the following string:
nothing to match
<-
this rocks should match as should this still and this rocks and still
->
should not match still or rocks
<- no matches here ->
And i want to find all matches of 'rocks' and 'still', but only when they are within <- ->
The purpose is to markup glossary words but be able to only mark them up in areas of text that are defined by the editor.
I currently have:
<-.*?(rocks|still).*?->
This unfortunately only matches the first 'rocks' and ignores all subsequent instances and all the 'still's
I have this in a Rubular
The usage of this will be somthing like
Regexp.new( '<-.*?(' + self.all.map{ |gt| gt.name }.join("|") + ').*?->', Regexp::IGNORECASE, Regexp::MULTILINE )
Thanks in advance for any help
There may be a way to do this with a single regex, but it will probably be simpler to just do it in two steps. First match all of the markups, and then search the markups for the glossary words:
text = <<END
nothing to match
<-
this rocks should match as should this still and this rocks and still
->
should not match still or rocks
<- no matches here ->
END
text.scan(/<-.*?->/m).each do |match|
print match.scan(/rocks|still/), "\n"
end
Also, you should probably note that regex is only a good solution here if there is never any nested markup (<-...<-...->...->) and no escaped <- or -> whether it is inside or outside of a markup.
Don't forget your Ruby string methods. Use them first before considering regular expressions
$ ruby -0777 -ne '$_.split("->").each{|x| x.split("<-").each{|y| puts "#{y}" if (y[/rocks.*still/]) } }' file
In Ruby, it depends on what you want to do with the regexp. You're matching a regular expression against a string, so you'll be using String methods. Certain of these will have an effect on all matches (e.g. gsub or rpartition); others will have an effect on only the first match (e.g. rindex, =~).
If you're working with any of the latter (that return only the first match), you'll want to make use of a loop that calls the method again, starting from a certain offset. For example:
# A method to print the indices of all matches
def print_match_indices(string, regex)
i = string.rindex(regex, 0)
while !i.nil? do
puts i
i = string.rindex(regex, i+1)
end
end
(Yes, you can use split first, but I expect that a regex loop like the foregoing would require fewer system resources.)
Edit: I solved this by using strip! to remove leading and trailing whitespaces as I show in this video. Then, I followed up by restoring the white space at the end of each string the array by iterating through and adding whitespace. This problem varies from the "dupe" as my intent is to keep the whitespace at the end. However, strip! will remove both the leading and trailing whitespace if that is your intent. (I would have made this an answer, but as this is incorrectly marked as a dupe, I could only edit my original question to include this.)
I have an array of words where I am trying to remove any whitespace that may exist at the beginning of the word instead of at the end. rstrip! just takes care of the end of a string. I want whitespaces removed from the beginning of a string.
example_array = ['peanut', ' butter', 'sammiches']
desired_output = ['peanut', 'butter', 'sammiches']
As you can see, not all elements in the array have the whitespace problem, so I can't just delete the first character as I would if all elements started with a single whitespace char.
Full code:
words = params[:word].gsub("\n", ",").delete("\r").split(",")
words.delete_if {|x| x == ""}
words.each do |e|
e.lstrip!
end
Sample text that a user may enter on the form:
Corn on the cob,
Fibonacci,
StackOverflow
Chat, Meta, About
Badges
Tags,,
Unanswered
Ask Question
String#lstrip (or String#lstrip!) is what you're after.
desired_output = example_array.map(&:lstrip)
More comments about your code:
delete_if {|x| x == ""} can be replaced with delete_if(&:empty?)
Except you want reject! because delete_if will only return a different array, rather than modify the existing one.
words.each {|e| e.lstrip!} can be replaced with words.each(&:lstrip!)
delete("\r") should be redundant if you're reading a windows-style text document on a Windows machine, or a Unix-style document on a Unix machine
split(",") can be replaced with split(", ") or split(/, */) (or /, ?/ if there should be at most one space)
So now it looks like:
words = params[:word].gsub("\n", ",").split(/, ?/)
words.reject!(&:empty?)
words.each(&:lstrip!)
I'd be able to give more advice if you had the sample text available.
Edit: Ok, here goes:
temp_array = text.split("\n").map do |line|
fields = line.split(/, */)
non_empty_fields = fields.reject(&:empty?)
end
temp_array.flatten(1)
The methods used are String#split, Enumerable#map, Enumerable#reject and Array#flatten.
Ruby also has libraries for parsing comma seperated files, but I think they're a little different between 1.8 and 1.9.
> ' string '.lstrip.chop
=> "string"
Strips both white spaces...
Ruby 1.9.1, OSX 10.5.8
I'm trying to write a simple app that parses through of bunch of java based html template files to replace a period (.) with an underscore if it's contained within a specific tag. I use ruby all the time for these types of utility apps, and thought it would be no problem to whip up something using ruby's regex support. So, I create a Regexp.new... object, open a file, read it in line by line, then match each line against the pattern, if I get a match, I create a new string using replaceString = currentMatch.gsub(/./, '_'), then create another replacement as whole string by newReplaceRegex = Regexp.escape(currentMatch) and finally replace back into the current line with line.gsub(newReplaceRegex, replaceString) Code below, of course, but first...
The problem I'm having is that when accessing the indexes within the returned MatchData object, I'm getting the first result twice, and it's missing the second sub string it should otherwise be finding. More strange, is that when testing this same pattern and same test text using rubular.com, it works as expected. See results here
My pattern:
(<(?:WEBOBJECT|webobject) (?:NAME|name)=(?:[a-zA-Z0-9]+.)+(?:[a-zA-Z0-9]+)(?:>))
Text text:
<WEBOBJECT NAME=admin.normalMode.someOtherPatternWeDontWant.moreThatWeDontWant>moreNonMatchingText<WEBOBJECT NAME=admin.SecondLineMatch>AndEvenMoreNonMatchingText
Here's the relevant code:
tagRegex = Regexp.new('(<(?:WEBOBJECT|webobject) (?:NAME|name)=(?:[a-zA-Z0-9]+\.)+(?:[a-zA-Z0-9]+)(?:>))+')
testFile = File.open('RegexTestingCompFix.txt', "r+")
lineCount=0
testFile.each{|htmlLine|
lineCount += 1
puts ("Current line: #{htmlLine} at line num: #{lineCount}")
tagMatch = tagRegex.match(htmlLine)
if(tagMatch)
matchesArray = tagMatch.to_a
firstMatch = matchesArray[0]
secondMatch = matchesArray[1]
puts "First match: #{firstMatch} and second match #{secondMatch}"
tagMatch.captures.each {|lineMatchCapture|
puts "Current capture for tagMatches: #{lineMatchCapture} of total match count #{matchesArray.size}"
#create a new regex using the match results; make sure to use auto escape method
originalPatternString = Regexp.escape(lineMatchCapture)
replacementRegex = Regexp.new(originalPatternString)
#replace any periods with underscores in a copy of lineMatchCapture
periodToUnderscoreCorrection = lineMatchCapture.gsub(/\./, '_')
#replace original match with underscore replaced copy within line
htmlLine.gsub!(replacementRegex, periodToUnderscoreCorrection)
puts "The modified htmlLine is now: #{htmlLine}"
}
end
}
I would think that I should get the first tag in matchData[0] then the second tag in matchData1, or, what I'm really doing because I don't know how many matches I'll get within any given line is matchData.to_a.each. And in this case, matchData has two captures, but they're both the first tag match
which is: <WEBOBJECT NAME=admin.normalMode.someOtherPatternWeDontWant.moreThatWeDontWant>
So, what the heck am I doing wrong, why does rubular test give me the expected results?
You want to use the on String#scan instead of the Regexp#match:
tag_regex = /<(?:WEBOBJECT|webobject) (?:NAME|name)=(?:[a-zA-Z0-9]+\.)+(?:[a-zA-Z0-9]+)(?:>)/
lines = "<WEBOBJECT NAME=admin.normalMode.someOtherPatternWeDontWant.moreThatWeDontWant>moreNonMatchingText\
<WEBOBJECT NAME=admin.SecondLineMatch>AndEvenMoreNonMatchingText"
lines.scan(tag_regex)
# => ["<WEBOBJECT NAME=admin.normalMode.someOtherPatternWeDontWant.moreThatWeDontWant>", "<WEBOBJECT NAME=admin.SecondLineMatch>"]
A few recommendations for next ruby questions:
newlines and spaces are your friends, you don't loose points for using more lines on your code ;-)
use do-end on blocks instead of {}, improves readability a lot
declare variables in snake case (hello_world) instead of camel case (helloWorld)
Hope this helps
I ended up using the String.scan approach, the only tricky point there was figuring out that this returns an array of arrays, not a MatchData object, so there was some initial confusion on my part, mostly due to my ruby green-ness, but it's working as expected now. Also, I trimmed the regex per Trevoke's suggestion. But snake case? Never...;-) Anyway, here goes:
tagRegex = /(<(?:webobject) (?:name)=(?:\w+\.)+(?:\w+)(?:>))/i
testFile = File.open('RegexTestingCompFix.txt', "r+")
lineCount=0
testFile.each do |htmlLine|
lineCount += 1
puts ("Current line: #{htmlLine} at line num: #{lineCount}")
oldMatches = htmlLine.scan(tagRegex) #oldMatches thusly named due to not explicitly using Regexp or MatchData, as in "the old way..."
if(oldMatches.size > 0)
oldMatches.each_index do |index|
arrayMatch = oldMatches[index]
aMatch = arrayMatch[0]
#create a new regex using the match results; make sure to use auto escape method
replacementRegex = Regexp.new(Regexp.escape(aMatch))
#replace any periods with underscores in a copy of lineMatchCapture
periodToUnderscoreCorrection = aMatch.gsub(/\./, '_')
#replace original match with underscore replaced copy within line, matching against the new escaped literal regex
htmlLine.gsub!(replacementRegex, periodToUnderscoreCorrection)
puts "The modified htmlLine is now: #{htmlLine}"
end # I kind of still prefer the brackets...;-)
end
end
Now, why does MatchData work the way it does? It seems like it's behavior is a bug really, and certainly not very useful in general if you can't get it provide a simple means of accessing all the matches. Just my $.02
Small bits:
This regexp helps you get "normalMode" .. But not "secondLineMatch":
<webobject name=\w+\.((?:\w+)).+> (with option 'i', for "case insensitive")
This regexp helps you get "secondLineMatch" ... But not "normalMode":
<webobject name=\w+\.((?:\w+))> (with option 'i', for "case insensitive").
I'm not really good at regexpt but I'll keep toiling at it.. :)
And I don't know if this helps you at all, but here's a way to get both:
<webobject name=admin.(\w+) (with option 'i').