Suppose I have a string:
content = "Please visit https://www.google.com...\nOr visit http://my.website.io\nhttp://myfriends.website.com\nOr https://www.myneigborsite.com, http://visit.me.com"
There are 5 urls in the string.
How do i count the urls using syntax?
I have tried using Regex.scan/2 |> Enum.count/1, or String.split/2 |> Enum.count/1 <- with regex but i always get wrong output.
I have also tried every http/https regex I found in the internet, but still I can't get the correct output.
Here's one that I've tried.
iex> content
...> |> String.split(~r/^(https?):\/\/[^\s$.?#].[^\s]*$/)
...> |> Enum.count()
...> |> Kernel.-(1)
-1
Another one with the same regex..
iex> Regex.scan(~r/^(https?):\/\/[^\s$.?#].[^\s]*$/, content) |> Enum.count()
0
but when I check if the regex matches some of the urls
iex> Regex.match?(~r/^(https?):\/\/[^\s$.?#].[^\s]*$/, "https://www.google.com")
true
iex(48)> Regex.match?(~r/^(https?):\/\/[^\s$.?#].[^\s]*$/, "http://my.website.io")
true
It does match.
I can't figure out what's the problem. Please help me.
You need to only count urls, which means you don’t need an overcomplicated regular expression.
~r|https?://[\w.-]+|
|> Regex.scan(content)
|> Enum.count()
#⇒ 5
Your attempts failed because you put $, the EOL-matcher in the expressions, which is obviously not matched when the URL is not terminating the string.
Related
I have code written in F# that iterates over an array of strings using regex to extract part of those strings. The problem is that the regex appears to randomly successfully match on some, but fail on others, even on an exact duplicates from the same list where it previously succeeded. What am I missing? Is this some sort of regex issue that I am not aware of?
Regex Pattern:
(?i)/(.*?/v\d/.*?((?=\?)|(?=\d)|(?=\n)))
F# code:
[<Literal>]
let ApiPattern = #"(?i)/(.*?/v\d/.*?((?=\?)|(?=\d)|(?=\n)))"
let parseOutEndpoints (inputs : (int * string) array) =
let regEx = new Regex(ApiPattern, RegexOptions.Compiled)
inputs |> Array.map (fun (id, path) -> [|id.ToString(); path|]) |> Array.collect (fun x -> x)
|> writeRawPathsToFile
File.ReadAllLines(RawPathsFile)
|> Array.map(fun (x) ->
let m = regEx.Match(x)
if m.Success
then
let endpoint = Domain.Endpoint(m.Value)
endpoint
else
let line = $"{x}"
File.AppendAllLines(FailedRegexMatches, [line], Encoding.UTF8)
Domain.NoEndpoint
)
Sample string array Data:
All of these should return a match, but don't. In comparison to this original list, a significantly reduced list of successful matches will be returned.
/enterprise-review/v9/choose?rr=Straight&pr=1%2E35239
/review-id-service/v1/business-id
/orderout/v1/vendor/shipping
/vendor-service/v1/Product/PartnerId/35310108
/Inspect/v1/Recommendation/Products/LaneId/0002,519188,13148,16939,7348,195982
/bin-inventory/v1/vendor?el=1%2E35239
/u-future/v1/fone?fhid=3028
/decline-summary/v1/details/card/65821974
/provide-service/v8/proDetails
/monetary-points/v1/sum/wins/681197
/listen-service/v1/audio-Details
/comment/v1/data
/comment/v1/data
/listen-service/v1/audio-Details
/comment/v1/data
/comment/v1/data
/listen-service/v1/audio-Details
/comment/v1/data
/comment/v1/data
This one helped to resolve your issue:
/(.*?/v\d/.*?((?=[\?\d\s])|$))
The reason behind problem: probably \r (windows carriage return), whitespaces and also end of string (noted as $ in regex).
Here's your regex and input in regexstorm, a .net Rex tester:
regex storm
I'd have made this a comment but RS's share urls contain the full Rex and input so it's too long for a comment (and SO doesn't allow url shorteners in comments)
So, my question is; does this look right to you? Are all the highlighted matches what you're expecting to match? If so, as RS's engine is .net based, I don't think there is a problem with the regex part of your code..
I want to write a regExp that only matches number (2) :
1)bincdf(2)
2)2*df(2)
3)2df(2)
3)2+df(2)
I working in as3, and I have a list of strings arr=['df','hsa','ksp'...]
Im matching those because I want to replace them, but the thing is there's not allowed to be any numbers or letters in front or behind. Behind there MUST be a '('.
So I would like to have the following result for the string = 'df':
2+df(2 -> TRUE
f+df(s -> TRUE
2+df2 -> FALSE
2*df+ -> FALSE
2+3df(2 -> FALSE
2-dF(2 -> FALSE
2-DF(2 -> FALSE
4+sdf(2 -> FALSE
++++++
PLEASE NOTICE
I want to replace the string that I pass 'df', so I ONLY want to match the string 'df'.
SO \frac(df(x) + 1,x) SHOULD ONLY MATCH the 'df(' part. So for example: if I want to replace the 'df' with '\df'. I would get:
\frac(\df(x) + 1,x)
after replace
I have tried using the ? regexp operator but I can't figure out the correct expression.
I greatly appreciate any help
You can try this. (?<=[^0-9a-z])df(?=\()
This ia a Demo on regex101.
As mentioned above, the goal is to remove square brackets and commas.
My current solution is the following:
Given:
"[40.45694301152436, -3.6907402812214514]"
|> String.replace("[", "")
|> String.replace(",", "")
|> String.replace("]", "")
|> String.split(" ")
|> Enum.map(fn x -> String.to_float(x) end)
Output:
[40.45694301152436, -3.6907402812214514]
I know this can be compacted much more, but I've been looking at examples all day and all failed to do the job above.
Instead of a string, you can pass a regex to String.replace. In Elixir you can build a regex with ~r sigil.
"[40.45694301152436, -3.6907402812214514]"
|> String.replace(~r'[\[\],]', "")
|> String.split()
|> Enum.map(&String.to_float/1)
While #fhdhsni has given you a great answer if your concern is readability I'd suggest abstracting the whole thing to a separate function like so:
defmodule T do
def parsefloats(stringtobeparsed) do
stringtobeparsed
|> String.replace("[", "")
|> String.replace(",", "")
|> String.replace("]", "")
|> String.split(" ")
|> Enum.map(fn x -> String.to_float(x) end)
end
end
Then you call it like so:
[x,y] = T.parsefloats("[40.45694301152436, -3.6907402812214514]")
# [40.45694301152436, -3.6907402812214514]
iex(3)> x
# 40.45694301152436
iex(4)> y
# -3.6907402812214514
Not any better in terms of more compact code but more readable I think.
Here's another option, using String.slice:
"[40.45694301152436, -3.6907402812214514]"
|> String.slice(1..-2)
|> String.split(~r/,\s+/)
|> Enum.map(&String.to_float/1)
Cheers!
Apart from the string replace solutions, you can take a look at Code.eval_string as well.
This way the string will get parsed and you'll get back the list you're looking for;
{list, _} = Code.eval_string "[40.45694301152436, -3.6907402812214514]"
# {[40.45694301152436, -3.6907402812214514], []}
I think the comment on your question about using a JSON parser is best, followed by fhdhsni's simple answer. But here's a method that extracts the numbers, rather than replacing the brackets:
str = "[40.45694301152436, -3.6907402812214514]"
regex = ~r/([\d\.-]+), ([\d\.+-]+)/
Regex.run(regex, str, capture: :all_but_first) |> Enum.map(&String.to_float/1)
Output:
[40.45694301152436, -3.6907402812214514]
I am new to programming and F# is my first .NET language.
As a beginner's project, I would like to write an application asking the user to enter a regex pattern and then flagging any errors.
I have looked through the Regex API on MSDN but there doesn't seem to be any methods that would automatically detect any errors in regex patterns. Will more experienced programmers kindly share with me how they would go about accomplishing this?
Thank you in advance for your help.
If you need to check if a regex compiles or not, simply use try-with block. If you need to check if a regex pattern matches your input string, use IsMatch() or .Success. That is quite enough.
An example with code taken from another SO post, but with an error in regex pattern where I replaced (http:\/\/\S+) with (http:\/\/\S+:
try
let testString = "http://www.bob.com http://www.b.com http://www.bob.com http://www.bill.com"
let matches input =
Regex.Matches(input, "(http:\/\/\S+")
|> Seq.cast<Match>
|> Seq.groupBy (fun m -> m.Value)
|> Seq.map (fun (value, groups) -> value, (groups |> Seq.length))
with
| :? System.Exception as ex -> printfn "Exception! %s " (ex.Message); None
More on F# exception raising can be found here or here.
I found this useful article on using Active Patterns with Regular Expressions:
http://www.markhneedham.com/blog/2009/05/10/f-regular-expressionsactive-patterns/
The original code snippet used in the article was this:
open System.Text.RegularExpressions
let (|Match|_|) pattern input =
let m = Regex.Match(input, pattern) in
if m.Success then Some (List.tl [ for g in m.Groups -> g.Value ]) else None
let ContainsUrl value =
match value with
| Match "(http:\/\/\S+)" result -> Some(result.Head)
| _ -> None
Which would let you know if at least one url was found and what that url was (if I understood the snippet correctly)
Then in the comment section Joel suggested this modification:
Alternative, since a given group may
or may not be a successful match:
List.tail [ for g in m.Groups -> if g.Success then Some g.Value else None ]
Or maybe you give labels to your
groups and you want to access them by
name:
(re.GetGroupNames()
|> Seq.map (fun n -> (n, m.Groups.[n]))
|> Seq.filter (fun (n, g) -> g.Success)
|> Seq.map (fun (n, g) -> (n, g.Value))
|> Map.ofSeq)
After trying to combine all of this I came up with the following code:
let testString = "http://www.bob.com http://www.b.com http://www.bob.com http://www.bill.com"
let (|Match|_|) pattern input =
let re = new Regex(pattern)
let m = re.Match(input) in
if m.Success then Some ((re.GetGroupNames()
|> Seq.map (fun n -> (n, m.Groups.[n]))
|> Seq.filter (fun (n, g) -> g.Success)
|> Seq.map (fun (n, g) -> (n, g.Value))
|> Map.ofSeq)) else None
let GroupMatches stringToSearch =
match stringToSearch with
| Match "(http:\/\/\S+)" result -> printfn "%A" result
| _ -> ()
GroupMatches testString;;
When I run my code in an interactive session this is what is output:
map [("0", "http://www.bob.com"); ("1", "http://www.bob.com")]
The result I am trying to achieve would look something like this:
map [("http://www.bob.com", 2); ("http://www.b.com", 1); ("http://www.bill.com", 1);]
Basically a mapping of each unique match found followed by the count of the number of times that specific matching string was found in the text.
If you think I'm going down the wrong path here please feel free to suggest a completely different approach. I'm somewhat new to both Active Patterns and Regular Expressions so I have no idea where to even begin in trying to fix this.
I also came up with this which is basically what I would do in C# translated to F#.
let testString = "http://www.bob.com http://www.b.com http://www.bob.com http://www.bill.com"
let matches =
let matchDictionary = new Dictionary<string,int>()
for mtch in (Regex.Matches(testString, "(http:\/\/\S+)")) do
for m in mtch.Captures do
if(matchDictionary.ContainsKey(m.Value)) then
matchDictionary.Item(m.Value) <- matchDictionary.Item(m.Value) + 1
else
matchDictionary.Add(m.Value, 1)
matchDictionary
Which returns this when run:
val matches : Dictionary = dict [("http://www.bob.com", 2); ("http://www.b.com", 1); ("http://www.bill.com", 1)]
This is basically the result I am looking for, but I'm trying to learn the functional way to do this, and I think that should include active patterns. Feel free to try to "functionalize" this if it makes more sense than my first attempt.
Thanks in advance,
Bob
Interesting stuff, I think everything you are exploring here is valid. (Partial) active patterns for regular expression matching work very well indeed. Especially when you have a string which you want to match against multiple alternative cases. The only thing I'd suggest with the more complex regex active patterns is that you give them more descriptive names, possibly building up a collection of different regex active patterns with differing purposes.
As for your C# to F# example, you can have functional solution just fine without active patterns, e.g.
let testString = "http://www.bob.com http://www.b.com http://www.bob.com http://www.bill.com"
let matches input =
Regex.Matches(input, "(http:\/\/\S+)")
|> Seq.cast<Match>
|> Seq.groupBy (fun m -> m.Value)
|> Seq.map (fun (value, groups) -> value, (groups |> Seq.length))
//FSI output:
> matches testString;;
val it : seq<string * int> =
seq
[("http://www.bob.com", 2); ("http://www.b.com", 1);
("http://www.bill.com", 1)]
Update
The reason why this particular example works fine without active patterns is because 1) you are only testing one pattern, 2) you are dynamically processing the matches.
For a real world example of active patterns, let's consider a case where 1) we are testing multiple regexes, 2) we are testing for one regex match with multiple groups. For these scenarios, I use the following two active patterns, which are a bit more general than the first Match active pattern you showed (I do not discard first group in the match, and I return a list of the Group objects, not just their values -- one uses the compiled regex option for static regex patterns, one uses the interpreted regex option for dynamic regex patterns). Because the .NET regex API is so feature filled, what you return from your active pattern is really up to what you find useful. But returning a list of something is good, because then you can pattern match on that list.
let (|InterpretedMatch|_|) pattern input =
if input = null then None
else
let m = Regex.Match(input, pattern)
if m.Success then Some [for x in m.Groups -> x]
else None
///Match the pattern using a cached compiled Regex
let (|CompiledMatch|_|) pattern input =
if input = null then None
else
let m = Regex.Match(input, pattern, RegexOptions.Compiled)
if m.Success then Some [for x in m.Groups -> x]
else None
Notice also how these active patterns consider null a non-match, instead of throwing an exception.
OK, so let's say we want to parse names. We have the following requirements:
Must have first and last name
May have middle name
First, optional middle, and last name are separated by a single blank space in that order
Each part of the name may consist of any combination of at least one or more letters or numbers
Input may be malformed
First we'll define the following record:
type Name = {First:string; Middle:option<string>; Last:string}
Then we can use our regex active pattern quite effectively in a function for parsing a name:
let parseName name =
match name with
| CompiledMatch #"^(\w+) (\w+) (\w+)$" [_; first; middle; last] ->
Some({First=first.Value; Middle=Some(middle.Value); Last=last.Value})
| CompiledMatch #"^(\w+) (\w+)$" [_; first; last] ->
Some({First=first.Value; Middle=None; Last=last.Value})
| _ ->
None
Notice one of the key advantages we gain here, which is the case with pattern matching in general, is that we are able to simultaneously test that an input matches the regex pattern, and decompose the returned list of groups if it does.