Here is one output that requires multiple regex evaluations but gets what I want to do done (remove everything except the text).
words = IO.read("file.txt").
gsub(/\s/, ""). # delete white spaces
gsub(".",""). # delete periods
gsub(",",""). # delete commas
gsub("?","") # delete Q marks
puts words
# output
# WheninthecourseofhumaneventsitbecomesnecessaryIwanttobelieveyoureallyIdobutwhoamItoblameWhenthefactsarecountedthenumberswillbereportedLotsoflaughsCharlieIthinkIheardthatonetentimesbefore
Looking at this post - Ruby gsub : is there a better way - I figured I would try to do a match to accomplish the same result without multiple regex evaluations. But I don't get the same output.
words = IO.read("file.txt").
match(/(\w*)+/)
puts words
# output - this only gets the first word
# When
And this only gets the first sentence:
words = IO.read("file.txt").
match(/(...*)+/)
puts words
# output - this only gets the first sentence
# When in the course of human events it becomes necessary.
Any suggestions on getting the same output (including stripping out white spaces and non-word characters) on a match rather than gsub?
You can do what you want in one gsub operation:
s = 'When in the course of human events it becomes necessary.'
s.gsub /[\s.,?]/, ''
# => "Wheninthecourseofhumaneventsitbecomesnecessary"
You don't need multiple regex evaluations for this.
str = "# output - this only gets the first sentence
# When in the course of human events it becomes necessary."
p str.gsub(/\W/, "")
#=>"outputthisonlygetsthefirstsentenceWheninthecourseofhumaneventsitbecomesnecessary"
Related
Working on a Ruby challenge to convert dash/underscore delimited words into camel casing. The first word within the output should be capitalized only if the original word was capitalized (known as Upper Camel Case).
My solution so far..:
def to_camel_case(str)
str.split('_,-').collect.camelize(:lower).join
end
However .camelize(:lower) is a rails method I believe and doesn't work with Ruby. Is there an alternative method, equally as simplistic? I can't seem to find one. Or do I need to approach the challenge from a completely different angle?
main.rb:4:in `to_camel_case': undefined method `camelize' for #<Enumerator: []:collect> (NoMethodError)
from main.rb:7:in `<main>'
I assume that:
Each "word" is made up of one or more "parts".
Each part is made of up characters other than spaces, hypens and underscores.
The first character of each part is a letter.
Each successive pair of parts is separated by a hyphen or underscore.
It is desired to return a string obtained by modifying each part and removing the hypen or underscore that separates each successive pair of parts.
For each part all letters but the first are to be converted to lowercase.
All characters in each part of a word that are not letters are to remain unchanged.
The first letter of the first part is to remain unchanged.
The first letter of each part other than the first is to be capitalized (if not already capitalized).
Words are separated by spaces.
It this describes the problem correctly the following method could be used.
R = /(?:(?<=^| )|[_-])[A-Za-z][^ _-]*/
def to_camel_case(str)
str.gsub(R) do |s|
c1 = s[0]
case c1
when /[A-Za-z]/
c1 + s[1..-1].downcase
else
s[1].upcase + s[2..-1].downcase
end
end
end
to_camel_case "Little Miss-muffet sat_on_HE$R Tuffett eating-her_cURDS And_whey"
# => "Little MissMuffet satOnHe$r Tuffett eatingHerCurds AndWhey"
The regular expression is can be written in free-spacing mode to make it self-documenting.
R = /
(?: # begin non-capture group
(?<=^| ) # use a positive lookbehind to assert that the next character
# is preceded by the beginning of the string or a space
| # or
[_-] # match '_' or '-'
) # end non-capture group
[A-Za-z] # match a letter
[^ _-]* # match 0+ characters other than ' ', '_' and '-'
/x # free-spacing regex definition mode
Most Rails methods can be added into basic Ruby projects without having to pull in the whole Rails source.
The trick is to figure out the minimum amount of files to require in order to define the method you need. If we go to APIDock, we can see that camelize is defined in active_support/inflector/methods.rb.
Therefore active_support/inflector seems like a good candidate to try. Let's test it:
irb(main)> require 'active_support/inflector'
=> true
irb(main)> 'foo_bar'.camelize
=> "FooBar"
Seems to work. Note that this assumes you already ran gem install activesupport earlier. If not, then do it first (or add it to your Gemfile).
In pure Ruby, no Rails, given str = 'my-var_name' you could do:
delimiters = Regexp.union(['-', '_'])
str.split(delimiters).then { |first, *rest| [first, rest.map(&:capitalize)].join }
#=> "myVarName"
Where str = 'My-var_name' the result is "MyVarName", since the first element of the splitting result is untouched, while the rest is mapped to be capitalized.
It works only with "dash/underscore delimited words", no spaces, or you need to split by spaces, then map with the presented method.
This method is using string splitting by delimiters, as explained here Split string by multiple delimiters,
chained with Object#then.
I have a file like this:
some content
some oterh
*********************
useful1 text
useful3 text
*********************
some other content
How do I get the content of the file within between two stars line in an array. For example, on processing the above file the content of array should be like this
a=["useful1 text" , "useful2 text"]
A really hack solution is to split the lines on the stars, grab the middle part, and then split that, too:
content.split(/^\*+$/)[1].split(/\s+/).reject(&:empty?)
# => ["useful1","useful3"]
f = File.open('test_doc.txt', 'r')
content = []
f.each_line do |line|
content << line.rstrip unless !!(line =~ /^\*(\*)*\*$/)
end
f.close
The regex pattern /^*(*)*$/ matches strings that contain only asterisks. !!(line =~ /^*(*)*$/) always returns a boolean value. So if the pattern does not match, the string is added to the array.
What about this:
def values_between(array, separator)
array.slice array.index(separator)+1..array.rindex(separator)-1
end
filepath = '/tmp/test.txt'
lines = %w(trash trash separator content content separator trash)
separator = "separator\n"
File.write '/tmp/test.txt', lines.join("\n")
values_between File.readlines('/tmp/test.txt'), "separator\n"
#=> ["content\n", "content\n"]
I'd do it like this:
lines = []
File.foreach('./test.txt') do |li|
lines << li if (li[/^\*{5}/] ... li[/^\*{5}/])
end
lines[1..-2].map(&:strip).select{ |l| l > '' }
# => ["useful1 text", "useful3 text"]
/^\*{5}/ means "A string that starts with and has at least five '*'.
... is one of two uses of .. and ... and, in this use, is commonly called a "flip-flop" operator. It isn't used often in Ruby because most people don't seem to understand it. It's sometimes mistaken for the Range delimiters .. and ....
In this use, Ruby watches for the first test, li[/^\*{5}/] to return true. Once it does, .. or ... will return true until the second condition returns true. In this case we're looking for the same delimiter, so the same test will work, li[/^\*{5}/], and is where the difference between the two versions, .. and ... come into play.
.. will return toggle back to false immediately, whereas ... will wait to look at the next line, which avoids the problem of the first seeing a delimiter and then the second seeing the same line and triggering.
That lets the test assign to lines, which, prior to the [1..-2].map(&:strip).select{ |l| l > '' } looks like:
# => ["*********************\n",
# "\n",
# "useful1 text\n",
# "\n",
# "useful3 text\n",
# "\n",
# "*********************\n"]
[1..-2].map(&:strip).select{ |l| l > '' } cleans that up by slicing the array to remove the first and last elements, strip removes leading and trailing whitespace, effectively getting rid of the trailing newlines and resulting in empty lines and strings containing the desired text. select{ |l| l > '' } picks up the lines that are greater than "empty" lines, i.e., are not empty.
See "When would a Ruby flip-flop be useful?" and its related questions, and "What is a flip-flop operator?" for more information and some background. (Perl programmers use .. and ... often, for just this purpose.)
One warning though: If the file has multiple blocks delimited this way, you'll get the contents of them all. The code I wrote doesn't know how to stop until the end-of-file is reached, so you'll have to figure out how to handle that situation if it could occur.
I am using Ruby1.9.3. I am newbie to this platform.
From the doc I just got familiared with two anchor which are \z and \G. Now I little bit played with \z to see how it works, as the definition(End or End of String) made me confused, I can't understand what it meant say - by End. So I tried the below small snippets. But still unable to catch.
CODE
irb(main):011:0> str = "Hit him on the head me 2\n" + "Hit him on the head wit>
=> "Hit him on the head me 2\nHit him on the head with a 24\n"
irb(main):012:0> str =~ /\d\z/
=> nil
irb(main):013:0> str = "Hit him on the head me 24 2\n" + "Hit him on the head >
=> "Hit him on the head me 24 2\nHit him on the head with a 24\n"
irb(main):014:0> str =~ /\d\z/
=> nil
irb(main):018:0> str = "Hit1 him on the head me 24 2\n" + "Hit him on the head>
=> "Hit1 him on the head me 24 2\nHit him on the head with a11 11 24\n"
irb(main):019:0> str =~ /\d\z/
=> nil
irb(main):020:0>
Every time I got nil as the output. So how the calculation is going on for \z ? what does End mean? - I think my concept took anything wrong with the End word in the doc. So anyone could help me out to understand the reason what is happening with the out why so happening?
And also i didn't find any example for the anchor \G . Any example please from you people to make visualize how \G used in real time programming?
EDIT
irb(main):029:0>
irb(main):030:0* ("{123}{45}{6789}").scan(/\G(?!^)\{\d+\}/)
=> []
irb(main):031:0> ('{123}{45}{6789}').scan(/\G(?!^)\{\d+\}/)
=> []
irb(main):032:0>
Thanks
\z matches the end of the input. You are trying to find a match where 4 occurs at the end of the input. Problem is, there is a newline at the end of the input, so you don't find a match. \Z matches either the end of the input or a newline at the end of the input.
So:
/\d\z/
matches the "4" in:
"24"
and:
/\d\Z/
matches the "4" in the above example and the "4" in:
"24\n"
Check out this question for example of using \G:
Examples of regex matcher \G (The end of the previous match) in Java would be nice
UPDATE: Real-World uses for \G
I came up with a more real world example. Say you have a list of words that are separated by arbitrary characters that cannot be well predicted (or there's too many possibilities to list). You'd like to match these words where each word is its own match up until a particular word, after which you don't want to match any more words. For example:
foo,bar.baz:buz'fuzz*hoo-har/haz|fil^bil!bak
You want to match each word until 'har'. You don't want to match 'har' or any of the words that follow. You can do this relatively easily using the following pattern:
/(?<=^|\G\W)\w+\b(?<!har)/
rubular
The first attempt will match the beginning of the input followed by zero non-word character followed by 3 word characters ('foo') followed by a word boundary. Finally, a negative lookbehind assures that the word which has just been matched is not 'har'.
On the second attempt, matching picks back up at the end of the last match. 1 non-word character is matched (',' - though it is not captured due to the lookbehind, which is a zero-width assertion), followed by 3 characters ('bar').
This continues until 'har' is matched, at which point the negative lookbehind is triggered and the match fails. Because all matches are supposed to be "attached" to the last successful match, no additional words will be matched.
The result is:
foo
bar
baz
buz
fuzz
hoo
If you want to reverse it and have all words after 'har' (but, again, not including 'har'), you can use an expression like this:
/(?!^)(?<=har\W|\G\W)\w+\b/
rubular
This will match either a word which is immediately preceeded by 'har' or the end of the last match (except we have to make sure not to match the beginning of the input). The list of matches is:
haz
fil
bil
bak
If you do want to match 'har' and all following words, you could use this:
/\bhar\b|(?!^)(?<=\G\W)\w+\b/
rubular
This produces the following matches:
har
haz
fil
bil
bak
Sounds like you want to know how Regex works? Or do you want to know how Regex works with ruby?
Check these out.
Regexp Class description
The Regex Coach - Great for testing regex matching
Regex cheat sheet
I understand \G to be a boundary match character. So it would tell the next match to start at the end of the last match. Perhaps since you haven't made a match yet you cant have a second.
Here is the best example I can find. Its not in ruby but the concept should be the same.
I take it back this might be more useful
I'm trying to write a regular expressions that will match a set of characters without regard to order. For example:
str = "act"
str.scan(/Insert expression here/)
would match:
cat
act
tca
atc
tac
cta
but would not match ca, ac or cata.
I read through a lot of similar questions and answers here on StackOverflow, but have not found one that matches my objectives exactly.
To clarify a bit, I'm using ruby and do not want to allow repeat characters.
Here is your solution
^(?:([act])(?!.*\1)){3}$
See it here on Regexr
^ # matches the start of the string
(?: # open a non capturing group
([act]) # The characters that are allowed and a capturing group
(?!.*\1) # That character is matched only if it does not occur once more, Lookahead assertion
){3} # Defines the amount of characters
$
The only special think is the lookahead assertion, to ensure the character is not repeated.
^ and $ are anchors to match the start and the end of the string.
[act]{3} or ^[act]{3}$ will do it in most regular expression dialects. If you can narrow down the system you're using, that will help you get a more specific answer.
Edit: as mentioned by #georgydyer in the comments below, it's unclear from your question whether or not repeated characters are allowed. If not, you can adapt the answer from this question and get:
^(?=[act]{3}$)(?!.*(.).*\1).*$
That is, a positive lookahead to check a match, and then a negative lookahead with a backreference to exclude repeated characters.
Here's how I'd go about it:
regex = /\b(?:#{ Regexp.union(str.split('').permutation.map{ |a| a.join }).source })\b/
# => /(?:act|atc|cat|cta|tac|tca)/
%w[
cat act tca atc tac cta
ca ac cata
].each do |w|
puts '"%s" %s' % [w, w[regex] ? 'matches' : "doesn't match"]
end
That outputs:
"cat" matches
"act" matches
"tca" matches
"atc" matches
"tac" matches
"cta" matches
"ca" doesn't match
"ac" doesn't match
"cata" doesn't match
I use the technique of passing an array into Regexp.union for a lot of things; I works especially well with the keys of a hash, and passing the hash into gsub for rapid search/replace on text templates. This is the example from the gsub documentation:
'hello'.gsub(/[eo]/, 'e' => 3, 'o' => '*') #=> "h3ll*"
Regexp.union creates a regex, and it's important to use source instead of to_s when extracting the actual pattern being generated:
puts regex.to_s
=> (?-mix:\b(?:act|atc|cat|cta|tac|tca)\b)
puts regex.source
=> \b(?:act|atc|cat|cta|tac|tca)\b
Notice how to_s embeds the pattern's flags inside the string. If you don't expect them you can accidentally embed that pattern into another, which won't behave as you expect. Been there, done that and have the dented helmet as proof.
If you really want to have fun, look into the Perl Regexp::Assemble module available on CPAN. Using that, plus List::Permutor, lets us generate more complex patterns. On a simple string like this it won't save much space, but on long strings or large arrays of desired hits it can make a huge difference. Unfortunately, Ruby has nothing like this, but it is possible to write a simple Perl script with the word or array of words, and have it generate the regex and pass it back:
use List::Permutor;
use Regexp::Assemble;
my $regex_assembler = Regexp::Assemble->new;
my $perm = new List::Permutor split('', 'act');
while (my #set = $perm->next) {
$regex_assembler->add(join('', #set));
}
print $regex_assembler->re, "\n";
(?-xism:(?:a(?:ct|tc)|c(?:at|ta)|t(?:ac|ca)))
See "Is there an efficient way to perform hundreds of text substitutions in Ruby?" for more information about using Regexp::Assemble with Ruby.
I will assume several things here:
- You are looking for permutations of given characters
- You are using ruby
str = "act"
permutations = str.split(//).permutation.map{|p| p.join("")}
# and for the actual test
permutations.include?("cat")
It is no regex though.
No doubt - the regex that uses positive/negative lookaheads and backreferences is slick, but if you're only dealing with three characters, I'd err on the side of verbosity by explicitly enumerating the character permutations like #scones suggested.
"act".split('').permutation.map(&:join)
=> ["act", "atc", "cat", "cta", "tac", "tca"]
And if you really need a regex out of it for scanning a larger string, you can always:
Regexp.union "act".split('').permutation.map(&:join)
=> /\b(act|atc|cat|cta|tac|tca)\b/
Obviously, this strategy doesn't scale if your search string grows, but it's much easier to observe the intent of code like this in my opinion.
EDIT: Added word boundaries for false positive on cata based on #theTinMan's feedback.
I'm doing some web scraping, this is the format for the data
Sr.No. Course_Code Course_Name Credit Grade Attendance_Grade
The actual string that i receive is of the following form
1 CA727 PRINCIPLES OF COMPILER DESIGN 3 A M
The things that I am interested in are the Course_Code, Course_Name and the Grade, in this example the values would be
Course_Code : CA727
Course_Name : PRINCIPLES OF COMPILER DESIGN
Grade : A
Is there some way for me to use a regular expression or some other technique to easily extract this information instead of manually parsing through the string.
I'm using jruby in 1.9 mode.
Let's use Ruby's named captures and a self-describing regex!
course_line = /
^ # Starting at the front of the string
(?<SrNo>\d+) # Capture one or more digits; call the result "SrNo"
\s+ # Eat some whitespace
(?<Code>\S+) # Capture all the non-whitespace you can; call it "Code"
\s+ # Eat some whitespace
(?<Name>.+\S) # Capture as much as you can
# (while letting the rest of the regex still work)
# Make sure you end with a non-whitespace character.
# Call this "Name"
\s+ # Eat some whitespace
(?<Credit>\S+) # Capture all the non-whitespace you can; call it "Credit"
\s+ # Eat some whitespace
(?<Grade>\S+) # Capture all the non-whitespace you can; call it "Grade"
\s+ # Eat some whitespace
(?<Attendance>\S+) # Capture all the non-whitespace; call it "Attendance"
$ # Make sure that we're at the end of the line now
/x
str = "1 CA727 PRINCIPLES OF COMPILER DESIGN 3 A M"
parts = str.match(course_line)
puts "
Course Code: #{parts['Code']}
Course Name: #{parts['Name']}
Grade: #{parts['Grade']}".strip
#=> Course Code: CA727
#=> Course Name: PRINCIPLES OF COMPILER DESIGN
#=> Grade: A
Just for fun:
str = "1 CA727 PRINCIPLES OF COMPILER DESIGN 3 A M"
tok = str.split /\s+/
data = {'Sr.No.' => tok.shift, 'Course_Code' => tok.shift, 'Attendance_Grade' => tok.pop,'Grade' => tok.pop, 'Credit' => tok.pop, 'Course_Name' => tok.join(' ')}
Do I see that correctly that the delimiter is always 3 spaces? Then just:
serial_number, course_code, course_name, credit, grade, attendance_grade =
the_string.split(' ')
Assuming everything except for the course description consists of single words and there are no leading or trailing spaces:
/^(\w+)\s+(\w+)\s+([\w\s]+)\s+(\w+)\s+(\w+)\s+(\w+)$/
Your example string will yield the following match groups:
1. 1
2. CA727
3. PRINCIPLES OF COMPILER DESIGN
4. 3
5. A
6. M
This answer isn't very idiomatic Ruby, because in this case I think clarity is better than being clever. All you really need to do to solve the problem you described is to split your lines with whitespace:
line = '1 CA727 PRINCIPLES OF COMPILER DESIGN 3 A M'
array = line.split /\t|\s{2,}/
puts array[1], array[2], array[4]
This assumes your data is regular. If not, you will need to work harder at tuning your regular expression and possibly handling edge cases where you don't have the required number of fields.
A Note for Posterity
The OP changed the input string, and modified the delimiter to a single space between fields. I'll leave my answer to the original question as-is (including the original input string for reference) as it may help others besides the OP in a less-specific case.