I've printed the code, wit ruby
string = "hahahah"
pring string.gsub("a","b")
How do I add more letter replacements into gsub?
string.gsub("a","b")("h","l") and string.gsub("a","b";"h","l")
didnt work...
*update I have tried this too but without any success .
letters = {
"a" => "l"
"b" => "n"
...
"z" => "f"
}
string = "hahahah"
print string.gsub(\/w\,letters)
You're overcomplicating. As with most method calls in Ruby, you can simply chain #gsub calls together, one after the other:
str = 'adfh'
print str.gsub("a","b").gsub("h","l") #=> 'bdfl'
What you're doing here is applying the second #gsub to the result of the first one.
Of course, that gets a bit long-winded if you do too many of them. So, when you find yourself stringing too many together, you'll want to look for a regex solution. Rubular is a great place to tinker with them.
The way to use your hash trick with #gsub and a regex expression is to provide a hash for all possible matches. This has the same result as the two #gsub calls:
print str.gsub(/[ah]/, {'a'=>'b', 'h'=>'l'}) #=> 'bdfl'
The regex matches either a or h (/[ah]/), and the hash is saying what to substitute for each of them.
All that said, str.tr('ah', 'bl') is the simplest way to solve your problem as specified, as some commenters have mentioned, so long as you are working with single letters. If you need to work with two or more characters per substitution, you'll need to use #gsub.
Related
How can I remove all newlines and spaces from a string in Ruby?
For example, if we have a string:
"123\n12312313\n\n123 1231 1231 1"
It should become this:
"12312312313123123112311"
That is, all whitespaces should be removed.
You can use something like:
var_name.gsub!(/\s+/, '')
Or, if you want to return the changed string, instead of modifying the variable,
var_name.gsub(/\s+/, '')
This will also let you chain it with other methods (i.e. something_else = var_name.gsub(...).to_i to strip the whitespace then convert it to an integer). gsub! will edit it in place, so you'd have to write var_name.gsub!(...); something_else = var_name.to_i. Strictly speaking, as long as there is at least one change made,gsub! will return the new version (i.e. the same thing gsub would return), but on the chance that you're getting a string with no whitespace, it'll return nil and things will break. Because of that, I'd prefer gsub if you're chaining methods.
gsub works by replacing any matches of the first argument with the contents second argument. In this case, it matches any sequence of consecutive whitespace characters (or just a single one) with the regex /\s+/, then replaces those with an empty string. There's also a block form if you want to do some processing on the matched part, rather than just replacing directly; see String#gsub for more information about that.
The Ruby docs for the class Regexp are a good starting point to learn more about regular expressions -- I've found that they're useful in a wide variety of situations where a couple of milliseconds here or there don't count and you don't need to match things that can be nested arbitrarily deeply.
As Gene suggested in his comment, you could also use tr:
var_name.tr(" \t\r\n", '')
It works in a similar way, but instead of replacing a regex, it replaces every instance of the nth character of the first argument in the string it's called on with the nth character of the second parameter, or if there isn't, with nothing. See String#tr for more information.
You could also use String#delete:
str = "123\n12312313\n\n123 1231 1231 1"
str.delete "\s\n"
#=> "12312312313123123112311"
You could use String#delete! to modify str in place, but note delete! returns nil if no change is made
Alternatively you could scan the string for digits /\d+/ and join the result:
string = "123\n\n12312313\n\n123 1231 1231 1\n"
string.scan(/\d+/).join
#=> "12312312313123123112311"
Please note that this would also remove alphabetical characters, dashes, symbols, basically everything that is not a digit.
I am looking to build a ruby regex to match multiple occurrences of a pattern and return them in an array. The pattern is simply: [[.+]]. That is, two left brackets, one or more characters, followed by two right brackets.
This is what I have done:
str = "Some random text[[lead:first_name]] and more stuff [[client:last_name]]"
str.match(/\[\[(.+)\]\]/).captures
The regex above doesn't work because it returns this:
["lead:first_name]] and another [[client:last_name"]
When what I wanted was this:
["lead:first_name", "client:last_name"]
I thought if I used a noncapturing group that for sure it should solve the issue:
str.match(/(?:\[\[(.+)\]\])+/).captures
But the noncapturing group returns the same exact wrong output. Any idea on how I can resolve my issue?
The problem with your regex is that the .+ part is "greedy", meaning that if the regex matches both a smaller and larger part of the string, it will capture the larger part (more about greedy regexes).
In Ruby (and most regex syntaxes), you can qualify your + quantifier with a ? to make it non-greedy. So your regex would become /(?:\[\[(.+?)\]\])+/.
However, you'll notice this still doesn't work for what you want to do. The Ruby capture groups just don't work inside a repeating group. For your problem, you'll need to use scan:
"[[a]][[ab]][[abc]]".scan(/\[\[(.+?)\]\]/).flatten
=> ["a", "ab", "abc"]
Try this:
=> str.match(/\[\[(.*)\]\].*\[\[(.*)\]\]/).captures
=> ["lead:first_name", "client:last_name"]
With many occurrences:
=> str
=> "Some [[lead:first_name]] random text[[lead:first_name]] and more [[lead:first_name]] stuff [[client:last_name]]"
=> str.scan(/\[(\w+:\w+)\]/)
=> [["lead:first_name"], ["lead:first_name"], ["lead:first_name"], ["client:last_name"]]
I Looking for an Regex to capture this examples of strings:
first_paramenter, first_hash_key: 'class1 class2', second_hash_key: true
first_argument, single_hash_key: 'class1 class2'
first_argument_without_second_argument
The pattern rules are:
The string must start some word (the first parameter) /^(\w+)/
The second parameter is optional
If second parameter provided, must have one comma after fisrt parameter
The second argument is an hash, with keys and values. Values can be true, false or an string enclosed by quotes
The hash keys must start with letter
I'm using this regex, but it matches with the only second example:
^(\w+),(\s[a-z]{1}[a-z_]+:\s'?[\w\s]+'?,?)$
I'd go with something like:
^(\w+)(?:, ([a-z]\w+): ('[^']*')(?:, ([a-z]\w+): (\w+))?)?
Here's a Rubular example of it.
(?:...) create non-capturing groups which we can easily test for existence using ?. That makes it easy to test for optional chunks.
([a-z]\w+) is an easy way to say "it must start with a letter" while allowing normal alpha, digits and "_".
As far as testing for "Values can be true, false or an string enclosed by quotes", I'd do that in code after capturing. It's way too easy to create a complex pattern, and then be unable to maintain it later. It's better to use simple ones, then look to see whether you got what you expected, than to try to enforce it inside the regex.
in the third example, your regex return 5 matches. It would be better if return only one. It's possible?
I'm not sure what you're asking. This will return a single capture for each, but why you'd want that makes no sense to me if you're capturing parameters to send to a method:
/^(\w+(?:, [a-z]\w+: '[^']*'(?:, [a-z]\w+: \w+)?)?)/
http://rubular.com/r/GLVuSOieI6
There is frequently a choice to be made between attacking an entire string with a single regex or breaking the string up with one or more String methods, and then going after each piece separately. The latter approach often makes debugging and testing easier, and may also make the code intelligible to mere mortals. It's always a judgement call, of course, but I think this problem lends itself well to the divide and conquer approach. This is how I'd do it.
Code
def match?(str)
a = str.split(',')
return false unless a.shift.strip =~ /^\w+$/
a.each do |s|
return false unless ((key_val = s.split(':')).size == 2) &&
key_val.first.strip =~ /^[a-z]\w*$/ &&
key_val.last.strip =~ /^(\'.*?\'|true|false)$/
end
true
end
Examples
match?("first_paramenter, first_hash_key: 'class1 class2',
second_hash_key: true")
#=>true
match?("first_argument, single_hash_key: 'class1 class2'")
#=>true
match?("first_argument_without_second_argument")
#=>true
match?("first_parameter, first_hash_key: 7")
#=>false
match?("dogs and cats, first_hash_key: 'class1 class2'")
#=>false
match?("first_paramenter, first_hash_key: 'class1 class2',
second_hash_key: :true")
#=>false
You've got the basic idea, you have a bunch of small mistakes in there
/^(\w+)(,\s[a-z][a-z_]+:\s('[^']*'|true|false))*$/
explained:
/^(\w+) # starts with a word
(
,\s # the comma goes _inside_ the parens since its optional
[a-z][a-z_]+:\s # {1} is completely redundant
( # use | in a capture group to allow different possible keys
'[^']*' | # note that '? doesn't make sure that the quotes always match
true |
false
)
)*$/x # can have 0 or more hash keys after the first word
I'm currently trying to rexp a string into multiple variables. Example string:
ryan_string = "RyanOnRails: This is a test"
I've matched it with this regexp, with 3 groups:
ryan_group = ryan_string.scan(/(^.*)(:)(.*)/i)
Now to access each group I have to do something like this:
ryan_group[0][0] (first group) RyanOnRails
ryan_group[0][1] (second group) :
ryan_group[0][2] (third group) This is a test
This seems pretty ridiculous and it feels like I'm doing something wrong. I would be expect to be able to do something like this:
g1, g2, g3 = ryan_string.scan(/(^.*)(:)(.*)/i)
Is this possible? Or is there a better way than how I'm doing it?
You don't want scan for this, as it makes little sense. You can use String#match which will return a MatchData object, you can then call #captures to return an Array of captures. Something like this:
#!/usr/bin/env ruby
string = "RyanOnRails: This is a test"
one, two, three = string.match(/(^.*)(:)(.*)/i).captures
p one #=> "RyanOnRails"
p two #=> ":"
p three #=> " This is a test"
Be aware that if no match is found, String#match will return nil, so something like this might work better:
if match = string.match(/(^.*)(:)(.*)/i)
one, two, three = match.captures
end
Although scan does make little sense for this. It does still do the job, you just need to flatten the returned Array first. one, two, three = string.scan(/(^.*)(:)(.*)/i).flatten
You could use Match or =~ instead which would give you a single match and you could either access the match data the same way or just use the special match variables $1, $2, $3
Something like:
if ryan_string =~ /(^.*)(:)(.*)/i
first = $1
third = $3
end
You can name your captured matches
string = "RyanOnRails: This is a test"
/(?<one>^.*)(?<two>:)(?<three>.*)/i =~ string
puts one, two, three
It doesn't work if you reverse the order of string and the regex.
You have to decide whether it is a good idea, but ruby regexp can (automagically) define local variables for you!
I am not yet sure whether this feature is awesome or just totally crazy, but your regex can define local variables.
ryan_string = "RyanOnRails: This is a test"
/^(?<webframework>.*)(?<colon>:)(?<rest>)/ =~ ryan_string
# This defined three variables for you. Crazy, but true.
webframework # => "RyanOnRails"
puts "W: #{webframework} , C: #{colon}, R: #{rest}"
(Take a look at http://ruby-doc.org/core-2.1.1/Regexp.html , search for "local variable").
Note:
As pointed out in a comment, I see that there is a similar and earlier answer to this question by #toonsend (https://stackoverflow.com/a/21412455). I do not think I was "stealing", but if you want to be fair with praises and honor the first answer, feel free :) I hope no animals were harmed.
scan() will find all non-overlapping matches of the regex in your string, so instead of returning an array of your groups like you seem to be expecting, it is returning an array of arrays.
You are probably better off using match(), and then getting the array of captures using MatchData#captures:
g1, g2, g3 = ryan_string.match(/(^.*)(:)(.*)/i).captures
However you could also do this with scan() if you wanted to:
g1, g2, g3 = ryan_string.scan(/(^.*)(:)(.*)/i)[0]
In Ruby, what regex will strip out all but a desired string if present in the containing string? I know about /[^abc]/ for characters, but what about strings?
Say I have the string "group=4&type_ids[]=2&type_ids[]=7&saved=1" and want to retain the pattern group=\d, if it is present in the string using only a regex?
Currently, I am splitting on & and then doing a select with matching condition =~ /group=\d/ on the resulting enumerable collection. It works fine, but I'd like to know the regex to do this more directly.
Simply:
part = str[/group=\d+/]
If you want only the numbers, then:
group_str = str[/group=(\d+)/,1]
If you want only the numbers as an integer, then:
group_num = str[/group=(\d+)/,1].to_i
Warning: String#[] will return nil if no match occurs, and blindly calling nil.to_i always returns 0.
You can try:
$str =~ s/.*(group=\d+).*/\1/;
Typically I wouldn't really worry too much about a complex regex. Simply break the string down into smaller parts and it becomes easier:
asdf = "group=4&type_ids[]=2&type_ids[]=7&saved=1"
asdf.split('&').select{ |q| q['group'] } # => ["group=4"]
Otherwise, you can use regex a bunch of different ways. Here's two ways I tend to use:
asdf.scan(/group=\d+/) # => ["group=4"]
asdf[/(group=\d+)/, 1] # => "group=4"
Try:
str.match(/group=\d+/)[0]