I have a xpath expression which I want to use to extract City and date from a td which contains a string of this kind:
City(may contain spaces and may be missing, but the following space is always present) on 2013/07/20
So far, I got to the following solution for extracting the date, which works partially:
//path/to/my/td/text()/replace(.,'(.*) on (.*)','$3')
This works when City is present, but when City is missing I get "on 2013/07/20" as a result.
I think this is because the first capturing group fails and so the number of groups is different.
How can I get this expression to work?
I did not fully check your regex, but it looks fine at first sight. Anyway, you can also go an easier way if you only want to get the date by extracting the text after "on ":
//path/to/my/td/text()/substring-after(.,'on ')
edit: or you may go the substring-way and select the last 10 characters of the content:
//path/to/my/td/text()/substring(., string-length(.) - 9)
Related
How can I extract the text up to the 4th instance of a character in a column?
I'm selecting text out of a column called filter_type up to the fourth > character.
To accomplish this, I've been trying to find the position of the fourth > character, but it's not working:
select substring(filter_type from 1 for position('>' in filter_type))
You can use the pattern matching function in Postgres.
First figure out a pattern to capture everything up to the fourth > character.
To start your pattern you should create a sub-group that captures non > characters, and one > character:
([^>]*>)
Then capture that four times to get to the fourth instance of >
([^>]*>){4}
Then, you will need to wrap that in a group so that the match brings back all four instances:
(([^>]*>){4})
and put a start of string symbol for good measure to make sure it only matches from the beginning of the String (not in the middle):
^(([^>]*>){4})
Here's a working regex101 example of that!
Once you have the pattern that will return what you want in the first group element (which you can tell at the online regex on the right side panel), you need to select it back in the SQL.
In Postgres, the substring function has an option to use a regex pattern to extract text out of the input using a 'from' statement in the substring.
To finish, put it all together!
select substring(filter_type from '^(([^>]*>){4})')
from filter_table
See a working sqlfiddle here
If you want to match the entire string whenever there are less than four instances of >, use this regular expression:
^(([^>]*>){4}|.*)
You can also use a simple, non-regex solution:
SELECT array_to_string((string_to_array(filter_type, '>'))[1:4], '>')
The above query:
splits your string into an array, using '>' as delimeter
selects only the first 4 elements
transforms the array back to a string
substring(filter_type from '^(([^>]*>){4})')
This form of substring lets you extract the portion of a string that matches a regex pattern.
You can also split the string, then choose the N'th element inside the result list. For example:
SELECT SPLIT_PART('aa,bb,cc', ',', 2)
will return: bb.
This function is defined as:
SPLIT_PART(string, delimiter, position)
In order to look at this problem, I did the following (all of the code below is available on the fiddle here):
CREATE TABLE s
(
a TEXT
);
I then created a PL/pgSQL function to generate random strings as follows.
CREATE FUNCTION f() RETURNS TEXT LANGUAGE SQL AS
$$
SELECT STRING_AGG(SUBSTR('abcdef>', CEIL(RANDOM() * 7)::INTEGER, 1), '')
FROM GENERATE_SERIES(1, 40)
$$;
I got the code from here and modified it so that it would produce strings with lots of > characters for testing purposes.
I then manually inserted a few strings at the beginning so that a quick look would tell me if the code was working as anticipated.
INSERT INTO s VALUES
('afsad>adfsaf>asfasf>afasdX>asdffs>asfdf>'),
('23433>433453>4>4559>455>3433>'),
('adfd>adafs>afadsf>'), -- only 3 '>'s!
('babedacfab>feaefbf>fedabbcbbcdcfefefcfcd'),
('e>>>>>'), -- edge case - multiple terminal '>'s
('aaaaaaa'); -- edge case - no '>'s whatsoever
The reason I put in the records with fewer than 4 >s is because the accepted answer (see discussion at the end of this answer) puts forward a solution which should return the entire string if this is the case!
On the fiddle, I then added 50,000 records as follows:
INSERT INTO s
SELECT f() FROM GENERATE_SERIES(1, 50000);
I also created a table s on a home laptop (16GB RAM, 500MB NVMe SSD) and populated it with 40,000,000 (50M) records - times also shown.
Now, my reading of the question is that we need to extract the string up to but not including the 4th > character.
The first solution (from treecon) was this one (I also show them running on the fiddle, but to save space here, I've only included the partial output of EXPLAIN (ANALYZE, BUFFERS, VERBOSE)) - the times shown are typical over a few runs:
EXPLAIN (ANALYZE, BUFFERS, VERBOSE)
SELECT
ARRAY_TO_STRING((STRING_TO_ARRAY(a, '>'))[1:4], '>'),
a
FROM s;
Result (only key parts included):
Seq Scan on public.s
Execution Time: 81.807 ms
40M Time: 46 seconds
A regex solution which works (significantly faster):
EXPLAIN (ANALYZE, BUFFERS, VERBOSE)
SELECT
SUBSTRING(a FROM '^(?:[^>]*>){0,3}[^>]*'),
a
FROM s;
Result:
Seq Scan on public.s
Execution Time: 74.757 ms
40M Time: 32 seconds
The accepted answer fails on many levels (see the fiddle). It leaves a > at the end and fails on various strings even when modified. Also, the solution proposed to include strings with fewer than 4 >s (i.e. ^(([^>]*>){4}|.*)) merely returns the original string (see end of fiddle).
I am using string replace method to clean-up column names.
df.columns=df.columns.str.replace("#$%./- ","").str.replace(' ', '_').str.replace('.', '_').str.replace('(','').str.replace(')','').str.replace('.','').str.lower()
Though it works, certainly does not look pythonic. Any suggestion?
I need only A-Za-z and underscore _ if required as column names.
Update:
I tried using Regular expression in the first replace method, but I still need to chain the string like this...
terms.columns=terms.columns.str.replace(r"^[^a-zA-Z1-9]*", '').str.replace(' ', '_').str.replace('(','').str.replace(')','').str.replace('.', '').str.replace(',', '')
Update showing test data:
Original string (Tab separated):
[Sr.No. Course Terms Besic of Education Degree Course Course Approving Authority (i.e Medical Council, etc.) Full form of Course 1 year Duration 2nd year 3rd year Duration 4 th year Duration]
Change column names:
terms.columns=terms.columns.str.replace(r"^[^a-zA-Z1-9]*", '').str.replace(' ', '_').str.replace('(','').str.replace(')','').str.replace('.', '').str.replace(',', '').str.lower()
Output:
['srno', 'course', 'terms', 'besic_of_education', 'degree_course',
'course_approving_authority_ie_medical_council_etc',
'full_form_of_course', '1_year_duration', '2nd_year_',
'3rd_year_duration', '4_th_year_duration']
Above output is correct. The question: Is there any way to achive the same other than the way I have used?
You can use a smaller number of .replace operations by replacing non-word strings with an empty string and subsequently removing the whitespace characters with an underscore.
df.columns.str.replace("[^\w\s]+","").str.replace("\s+","_").str.lower()
I hope this helps.
I'm looking in a sql table through a bunch of names and I want to get a list of all the different titles used. e.g. SNR, MRS, MR, JNR etc
Sometimes there is an entry that might have 2 titles, e.g: MR NAME NAME JNR. I want both of these titles 'MR' & 'JNR'
I thought a good way to do this would be with regex and find any names that have 2 or 3 characters. A title at the front would be followed by a space, while a title at the end would be preceded by one. So I have:
/(^[A-Z]{2,3})\s|\s(^[A-Z]{2,3}$)/
a regex101 example here.
As you can see I've used 'match either A or B' thing. If I throw at it a name with a title at either the start or finish, I end up getting what I want, but I don't know how to tell it to get both. i.e. strings with 2 titles will only give me back one match.
How do I get both?
Instead of an "OR", you could just match any character in between:
(^[A-Z]{3})\s.*\s([A-Z]{3}$)
I have a column called user_response, on which I want to do variety of operations like take out words contained in quotes, and take out the part of the string after colon (:)
One such operation is this:
Let's say for a record
user_response = "My company: 'XYZ Co.' has allowed to use:: the following \n \n kind of product: RealMadridTShirts"
Now, I want to scrape the part of the string after last colon(:). Hence, my output should be RealMadridTShirts
I could achieve this somehow with the following hack:
SELECT reverse(split_part(reverse(user_response), ' :', 1))
However, this is grossly inefficient, specially when I am having to do this over 500,000 rows. It's not an operation that I will doing throughout the day. This operation is for a once-a-day load but even then the load is becoming very expensive.
Coming from Oracle, I know I could have used INSTR and SUBSTR functions to achieve it in a more elegant fashion (without having to reverse the string and all.
Also, what if I had to scrape the text after the second last colon?
Find the string after the last colon, right?
My company: 'XYZ Co.' has allowed to use:: the following \n \n kind of product: RealMadridTShirts
It's trivial with a regular expression:
regress=> SELECT (regexp_matches(
'My company: ''XYZ Co.'' has allowed to use:: the following \n \n kind of product: RealMadridTShirts',
'.*:(.*?)$')
)[1];
regexp_matches
--------------------
RealMadridTShirts
(1 row)
The apparent lack of a function to request the position of a string counting from a particular starting point makes it harder to do without using a regexp, but as a regexp is sure to be the fastest way to solve this I doubt that's an issue.
Your bigger problem is likely to be that you're scanning so much data. That's never going to be fast.
I'm converting a text file to a Tab-Delimited text file, and ran into a bit of a snag. I can get everything I need to work the way I want except for one small part.
One field I'm working with has the home addresses of the subjects as a single entry ("1234 Happy Lane Somewhere, St 12345") and I need each broken down by Street(Tab)City(Tab)State(Tab)Zip. The one part I'm hung up on is the Tab between the State and the Zip.
I've been using input=input.Replace throughout, and it's worked well so far, but I can't think of how to untangle this one. The wildcards I'm used to don't seem to be working, I can't replace ("?? #####") with ("??" + ControlChars.Tab + "#####")...which I honestly didn't expect to work, but it's the only idea on the matter I had.
I've read a bit about using Regex, but have no experience with it, and it seems a bit...overwhelming.
Is Regex my best option for this? If not, are there any other suggestions on solutions I may have missed?
Thanks for your time. :)
EDIT: Here's what I'm using so far. It makes some edits to the line in question, taking care of spaces, commas, and other text I don't need, but I've got nothing for the State/Zip situation; I've a bad habit of wiping something if it doesn't work, but I'll append the last thing I used to the very end, if that'll help.
If input Like "Guar*###/###-####" Then
input = input.Replace("Guar:", "")
input = input.Replace(" ", ControlChars.Tab)
input = input.Replace(",", ControlChars.Tab)
input = "C" + ControlChars.Tab + strAccount + ControlChars.Tab + input
End If
input = System.Text.RegularExpressions.Regex.Replace(" #####", ControlChars.Tab + "#####") <-- Just one example of something that doesn't work.
This is what's written to input in this example
" Guar: LASTNAME,FIRSTNAME 999 E 99TH ST CITY,ST 99999 Tel: 999/999-9999"
And this is what I can get as a result so far
C 99999/9 LASTNAME FIRSTNAME 999 E 99TH ST CITY ST 99999 999/999-9999
With everything being exactly what I need besides the "ST 99999" bit (with actual data obviously omitted for privacy and professional whatnots).
UPDATE: Just when I thought it was all squared away, I've got another snag. The raw data gives me this.
# TERMINOLOGY ######### ##/##/#### # ###.##
And the end result is giving me this, because this is a chunk of data that was just fine as-is...before I removed the Tabs. Now I need a way to replace them after they've been removed, or to omit this small group of code from a document-wide Tab genocide I initiate the code with.
#TERMINOLOGY###########/##/########.##
Would a variant on rgx.Replace work best here? Or can I copy the code to a variable, remove Tabs from the document, then insert the variable without losing the tabs?
I think what you're looking for is
Dim r As New System.Text.RegularExpressions.Regex(" (\d{5})(?!\d)")
Dim input As String = rgx.Replace(input, ControlChars.Tab + "$1")
The first line compiles the regular expression. The \d matches a digit, and the {5}, as you can guess, matches 5 repetitions of the previous atom. The parentheses surrounding the \d{5} is known as a capture group, and is responsible for putting what's captured in a pseudovariable named $1. The (?!\d) is a more advanced concept known as a negative lookahead assertion, and it basically peeks at the next character to check that it's not a digit (because then it could be a 6-or-more digit number, where the first 5 happened to get matched). Another version is
" (\d{5})\b"
where the \b is a word boundary, disallowing alphanumeric characters following the digits.