Extracting dates that are in different formats using regex and sorting them - pandas

Question

I am new to text mining and I need to extract the dates from a *.txt file and sort them. The dates are in between the sentences ( each line) and their format can potentially

Answer 1

I think this is one of the coursera text mining assignment. Well you can use regex and extract to get the solution. dates.txt i.e

doc = []
with open('dates.txt') as file:
    for line in file:
        doc.append(line)

df = pd.Series(doc)

def date_sorter():
    # Get the dates in the form of words
    one = df.str.extract(r'((?:\d{,2}\s)?(?:Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec)[a-z]*(?:-|\.|\s|,)\s?\d{,2}[a-z]*(?:-|,|\s)?\s?\d{2,4})')
    # Get the dates in the form of numbers
    two = df.str.extract(r'((?:\d{1,2})(?:(?:\/|-)\d{1,2})(?:(?:\/|-)\d{2,4}))')
    # Get the dates where there is no days i.e only month and year  
    three = df.str.extract(r'((?:\d{1,2}(?:-|\/))?\d{4})')
    #Convert the dates to datatime and by filling the nans in two and three. Replace month name because of spelling mistake in the text file.
    dates = pd.to_datetime(one.fillna(two).fillna(three).replace('Decemeber','December',regex=True).replace('Janaury','January',regex=True))
return pd.Series(dates.sort_values())

date_sorter()

Output:

9     1971-04-10
84    1971-05-18
2     1971-07-08
53    1971-07-11
28    1971-09-12
474   1972-01-01
153   1972-01-13
13    1972-01-26
129   1972-05-06
98    1972-05-13
111   1972-06-10
225   1972-06-15
31    1972-07-20
171   1972-10-04
191   1972-11-30
486   1973-01-01
335   1973-02-01
415   1973-02-01
36    1973-02-14
405   1973-03-01
323   1973-03-01
422   1973-04-01
375   1973-06-01
380   1973-07-01
345   1973-10-01
57    1973-12-01
481   1974-01-01
436   1974-02-01
104   1974-02-24
299   1974-03-01

If you want to return only the index then return pd.Series(dates.sort_values().index)

Parsing of first regex

 #?: Non-capturing group 

((?:\d{,2}\s)? # The two digits group. `?` refers to preceding token or group. Here the digits of 2 or 1 and space occurring once or less.  

 (?:Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec)[a-z]* # The words in group ending with any letters `[]` occuring any number of times (`*`). 

 (?:-|\.|\s|,) # Pattern matching -,.,space 

 \s? #(`?` here it implies only to space i.e the preceding token)

 \d{,2}[a-z]* # less than or equal to two digits having any number of letters at the end (`*`). (Eg: may be 1st, 13th , 22nd , Jan , December etc ) . 

 (?:-|,|\s)?# The characters -/,/space may occur once and may not occur because of `?` at the end

 \s? # space may occur or may not occur at all (maximum is 1) (`?` here it refers only to space)

 \d{2,4}) # Match digit which is 2 or 4   

Hope it helps.