Extracting each unique data from a string [closed] - regex

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I have been trying to set up REGEX extraction process for the following to no avail.
I have a set of date values in the formats to follow. I need to be able to extract these as unique individual dates.
If there is a single value, it is a standard simple format of mm/dd/yyyy. That one is easy.
If there are more than one date value, then it can be in a format as follows:
Feb 5, 12, 19, 26, Mar 4, 11 2016
I need to turn these into 02/05/2016, 02/12/2016, etc.
Eventually I will be inserting these dates into a database.
Am I going about this in the wrong way? Thanks for advice.

Answer 1

This will be complete spaghetti if you try to do it with one regex:
You will have to hardcode the names of the months and the corresponding numbers somewhere.
The year doesn't follow after the list of days of the month, rather after the list of all month names - month days this year.
However with a little help from a normal programming language you can still get a short and regex-centric solution. Here is a small Ruby snippet to show the general idea:
# this is the input
dates = "Feb 5, 12, 19, 26, Mar 4, 11 2016, Jul 5, 7, 19, 26, May 4, 11 2017"
# a hash with month name => month number
MONTHS = {
'Jan' => '01',
'Feb' => '02',
'Mar' => '03',
'Apr' => '04',
'May' => '05',
'Jun' => '06',
'Jul' => '07',
'Aug' => '08',
'Sep' => '09',
'Oct' => '10',
'Nov' => '11',
'Dec' => '12',
}
# match and extract three things:
# month - the first found month name (three letters)
# days - list of days separated by commas and spaces for this month
# for example 5, 12, 19, 26,
# year - the first found year (four digits)
# ,? is because we don't have , after the last day of the year
while dates =~ /(\w{3}) ((?:\d\d?,? )+).*?(\d{4})/
month, days, year = $1, $2, $3
# to each day collate a date in the wanted format
# MONTHS[month] gets the month number from the hash above
# sprintf simply makes sure that one digit days will have a leading 0
dates_this_month = days.split(/,? /).map do |day|
"#{MONTHS[month]}/#{sprintf('%02d', day)}/#{year}"
end.join ', '
# substitute the dates for this month with the new format
dates.sub! "#{month} #{days}", "#{dates_this_month}, "
end
# remove leftover years
dates.gsub! /, \d{4}/, ''
Now dates is in the desired format.

Answer 2

Assuming that there are no deviations or anomalies in the data that you're RegExing, the following RegEx can be applied with case-sensitivity set and allow you to access the information you need. With RegExs, it's important to "know your data" because this variable can greatly alter the construction of a RegEx -- the balance between specificity and clarity is important since RegExs can easily become unwieldy and cryptic.
Save the months as: ([A-Z][a-z][a-z]) // this can be your $1 variable (useful later)
Save the day values as: \s*(?:([0-9]?[0-9]),\s)* // $2 variable should work for access to this list of values
Save the year values as: ([0-9]{4,4}) // $3 variable should work for accessing these values NOTE: this only works for #### formatted dates by design although it can be altered to handle different formats; I'm just going off of the example you provided
Stringing it all together you get: (?:([A-Z][a-z][a-z])\s*(?:([0-9]?[0-9]),\s)*)+([0-9]{4,4})
You can then construct objects with these values so that you don't end up with a bunch of chaotic data. Let me know if I addressed you problem properly. If there's something that I missed or some additional functionality that you forgot to mention, I will be happy to assist.