Regular Expressions - change format of a date value

Jim:

Correct, I am not using them.

I was importing raw string values and was not sure what I would encounter.  Since "string" types are the most flexible, that is what I used.  Now I want to go back and format the values I can to the format I indicated.

The data type of the column containing the date type strings is   nvarchar(200)

Off work ...  back in 16 hours ... starting ..... now ....  :)

A simplistic regular expression to match what you want follows.  I'm not sure if your date values are within a longer string or by themselves.  This code will only match dates at the beginning of the string.  Done in C# (is that what you are using?).

Match m = Regex.Match(your_date_string, @"^(\d{1,2})(-|/)(\d{1,2})(-|/)(\d{4})"); 
if (m.Success)
{
   string result = String.Format("{0:D4}{1:D2}{2:D2}", int.Parse(m.Groups[5].Value),int.Parse(m.Groups[1].Value), int.Parse(m.Groups[3].Value)); 
...
}

                                              

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Yes, I am using C#.

I will usually trim the strings before performing any operations on them.

Jim:

Your regular expression works great.  The points are yours.

I was wondering if you could help me refine the idea further?


I want to take the following method and make it more generic.  Meaning, you would pass-in the pattern AND the action as parameters, and then have the matching take place and the action taken based on that.  Not just for operating on Date values, but based upon whatever is passed in.


Is there a way to genericize this stuff:

int.Parse(m.Groups[5].Value),
int.Parse(m.Groups[1].Value),
int.Parse(m.Groups[3].Value)

public class RegExpr : ICharacterCleaners
    {
        public string rulename = "";
        public string regexchars = "";
        public string actiontoperform = "";
 
        public string DoWork(string CurValue)
        {
            string result = "";
            //YYYYMMDD detection
            //^(\d{1,2})(-|/)(\d{1,2})(-|/)(\d{4})
            Match m = Regex.Match(CurValue, @regexchars);
            if (m.Success)
            {
                //"{0:D4}{1:D2}{2:D2}"
                result = String.Format(actiontoperform, int.Parse(m.Groups[5].Value), int.Parse(m.Groups[1].Value), int.Parse(m.Groups[3].Value));
            }
 
            return result;
 
        }
    }

                                              

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Started experimenting in the Immediate Window:

m.Groups[0].Value
"1/5/2009"
m.Groups[1].Value
"1"
m.Groups[2].Value
"/"
m.Groups[3].Value
"5"
m.Groups[4].Value
"/"
m.Groups[5].Value
"2009"


I think I can see what is happening here.....

Still not sure how to capture how many GROUPS there are or which ones are relevant --  especially when I am just working with patterns, not necessarily ones that deal with dates.

Are you sure it needs to be more generic?  The actual matching and formatting is tied together and is basic as far as functionality.

I'm not sure what problem you're solving though.  You could create a delegate/closure containing just the matching and formatting code for each case you need to handle then use those in another method to actually execute the actions in a generic fashion.

For transforming the DATE value from

mm/dd/yyyy

to

yyyymmdd

you have to know that Groups[5].Value is the YEAR and so forth.


I want to be able to pass in a pattern and then work upon that pattern  WITHOUT having to know this.

Match m = Regex.Match(your_date_string, @"^(?'month'\d{1,2})(-|/)(?'day'\d{1,2})(-|/)(?'year'\d{4})");
if (m.Success)
{
   string result = String.Format("{0:D4}{1:D2}{2:D2}", int.Parse(m.Groups["year"].Value),int.Parse(m.Groups["month"].Value), int.Parse(m.Groups["day"].Value));
...
}


This is better, and friendier, but I am still not sure how generic it is.







Let's forget dates for a moment.

Let's say I wanted to use the    "DoWork( )" method for ANY sort of matching, not just dates.


For example, if I wanted to replace all "-" with " "  in a string.

"The-quick-brown-fox-jumped"

becomes

"The quick brown fox jumped"


All we need to do is change the pattern to look for "-"   instead of for  "MM <seperator> DD <seperator> YYYY"


But your method as it is written will not handle this properly.  I want to be able to pass in not just ANY pattern, but also pass in WHAT I want to happen to that pattern, whether it be the re-arranging of the GROUP values, or a simple subsitution of one value for another.

something like:

Match m = Regex.Match(ANYSTRING, @PATTERN TO MATCH);
if (m.Success)
{
   string result = String.Format(FORMATTING,  ORDER OF VARIABLES);
...
}


Is there a way to provide  FORMATTING and  WHAT TO DO WITH THE GROUPS    as regular expressions?

The original string
The pattern
The formatting
Which groups to use and what they are called

None of this will be known until runtime.

Jim:


This  MIGHT be what I want:

static string MDYToDMY(string input)
{
     return Regex.Replace(input,
         "\\b(?<month>\\d{1,2})/(?<day>\\d{1,2})/(?<year>\\d{2,4})\\b",
         "${day}-${month}-${year}");
}

this provides the pattern as well as what the replacement text looks like.....


I'll have to play around with it some more to see if it handles different conditions, not just dates, but other scenarios.....

Yes, Replace might work depending on your needs.  In fact, I probably should have put that in the original solution but I wasn't sure what your input data looked like.

This is almost working PERFECTLY:

The only problem is that it is not PADDING the single digit months and days with a ZERO.

What do I do to make sure that happens?

public string DoWork(string CurValue)
        {
            string result = "";
 
            Match m = Regex.Match(CurValue, @regexchars);
 
            if (m.Success)
            {
                result = Regex.Replace(CurValue, @regexchars, @actiontoperform);
 
            }
 
            return result;
 
        }

                                              

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Sorry, here are the parameters:

CurValue = "5/1/2009"
regexchars = "^(?'month'\\d{1,2})(-|/)(?'day'\\d{1,2})(-|/)(?'year'\\d{4})"
actiontoperform = "${year}${month}${day}"


What change do I make to actiontoperform so that it will pad single digit days and months with a "0" ???


Thanks for all the help, btw.


Tom

Right, that's the problem with not using the String.Format.

Regex.Replace supports a MatchEvaluator argument instead of the normal replacement string.  That's a delegate which could be used to return the padded result.  It gets passed the Match object that matched and it would have to figure out what to do with each (probably based on the name of the match group).  I'm not sure how you could code that into a dynamic interface like you're trying to do without a bunch of work.

One thing you might try is to take all the matches in m.Groups and put them into an array, then pass that array as the second argument to String.Format.   So it would be like:  String.Format("format_string", array_of_matches).   Then in your format_string you can reference any item in the array, either by name or array index (for example, the "{0:D2}" format would reference index 0 in the array).

Gah!!!!!!!!!!

So close!!!!!!!

My gut tells me your suggestion is the way I will end-up going.


Thanks...

Jim:

Can you provide an example of calling a delegate inside Replace(  )  ?


Tom

If you look at the C# example here it should give you an idea:
http://msdn.microsoft.com/en-us/library/system.text.regularexpressions.matchevaluator.aspx

Unfortunately I can't be more specific as I don't have time today.  :)

I would consider the other approach though.  Copying all the matches from m.Groups into an array then using that in the String.Format.  That is more like the original solution but should be more flexible.