I would like to know if either/both of these two scenarios are possible in Lua:
I have a string that looks like such: some_value=averylongintegervalue
Say I know there are exactly 21 characters after the = sign in the string, is there a short way to replace the string averylongintegervalue with my own? (i.e. a simpler way than typing out: string.gsub("some_value=averylongintegervalue", "some_value=.....................", "some_value=anewintegervalue")
Say we edit the original string to look like such: some_value=averylongintegervalue&
Assuming we do not know how many characters is after the = sign, is there a way to replace the string in between the some_value= and the &?
I know this is an oddly specific question but I often find myself needing to perform similar tasks using regex and would like to know how it would be done in Lua using pattern-matching.
Yes, you can use something like the following (%1 refers to the first capture in the pattern, which in this case captures some_value=):
local str = ("some_value=averylongintegervalue"):gsub("(some_value=)[^&]+", "%1replaced")
This should assign some_value=replaced.
Do you know if it is also possible to replace every character between the = and & with a single character repeated (such as a * symbol repeated 21 times instead of a constant string like replaced)?
Yes, but you need to use a function:
local str = ("some_value=averylongintegervalue")
:gsub("(some_value=)([^&]+)", function(a,b) return a..("#"):rep(#b) end)
This will assign some_value=#####################. If you need to limit this to just one replacement, then add ,1 as the last parameter to gsub (as Wiktor suggested in the comment).
Related
I am working with a messy manually maintained "database" that has a column containing a string with name,value pairs. I am trying to parse the entire column with regexp to pull out the values. The column is huge (>100,000 entries). As a proxy for my actual data, let's use this code:
line1={'''thing1'': ''-583'', ''thing2'': ''245'', ''thing3'': ''246'', ''morestuff'':, '''''};
line2={'''thing1'': ''617'', ''thing2'': ''239'', ''morestuff'':, '''''};
line3={'''thing1'': ''unexpected_string(with)parens5'', ''thing2'': 245, ''thing3'':''246'', ''morestuff'':, '''''};
mycell=vertcat(line1,line2,line3);
This captures the general issues encountered in the database. I want to extract what thing1, thing2, and thing3 are in each line using cellfun to output a scalar cell array. They should normally be 3 digit numbers, but sometimes they have an unexpected form. Sometimes thing3 is completely missing, without the name even showing up in the line. Sometimes there are minor formatting inconsistencies, like single quotes missing around the value, spaces missing, or dashes showing up in front of the three digit value. I have managed to handle all of these, except for the case where thing3 is completely missing.
My general approach has been to use expressions like this:
expr1='(?<=thing1''):\s?''?-?([\w\d().]*?)''?,';
expr2='(?<=thing2''):\s?''?-?([\w\d().]*?)''?,';
expr3='(?<=thing3''):\s?''?-?([\w\d().]*?)''?,';
This looks behind for thingX' and then tries to match : followed by zero or one spaces, followed by 0 or 1 single quote, followed by zero or one dash, followed by any combination of letters, numbers, parentheses, or periods (this is defined as the token), using a lazy match, until zero or one single quote is encountered, followed by a comma. I call regexp as regexp(___,'tokens','once') to return the matching token.
The problem is that when there is no match, regexp returns an empty array. This prevents me from using, say,
out=cellfun(#(x) regexp(x,expr3,'tokens','once'),mycell);
unless I call it with 'UniformOutput',false. The problem with that is twofold. First, I need to then manually find the rows where there was no match. For example, I can do this:
emptyout=cellfun(#(x) isempty(x),out);
emptyID=find(emptyout);
backfill=cell(length(emptyID),1);
[backfill{:}]=deal('Unknown');
out(emptyID)=backfill;
In this example, emptyID has a length of 1 so this code is overkill. But I believe this is the correct way to generalize for when it is longer. This code will change every empty cell array in out with the string Unknown. But this leads to the second problem. I've now got a 'messy' cell array of non-scalar values. I cannot, for example, check unique(out) as a result.
Pardon the long-windedness but I wanted to give a clear example of the problem. Now my actual question is in a few parts:
Is there a way to accomplish what I'm trying to do without using 'UniformOutput',false? For example, is there a way to have regexp pass a custom string if there is no match (e.g. pass 'Unknown' if there is no match)? I can think of one 'cheat', which would be to use the | operator in the expression, and if the first token is not matched, look for something that is ALWAYS found. I would then still need to double back through the output and change every instance of that result to 'Unknown'.
If I take the 'UniformOutput',false approach, how can I recover a scalar cell array at the end to easily manipulate it (e.g. pass it through unique)? I will admit I'm not 100% clear on scalar vs nonscalar cell arrays.
If there is some overall different approach that I'm not thinking of, I'm also open to it.
Tangential to the main question, I also tried using a single expression to run regexp using 3 tokens to pull out the values of thing1, thing2, and thing3 in one pass. This seems to require 'UniformOutput',false even when there are no empty results from regexp. I'm not sure how to get a scalar cell array using this approach (e.g. an Nx1 cell array where each cell is a 3x1 cell).
At the end of the day, I want to build a table using these results:
mytable=table(out1,out2,out3);
Edit: Using celldisp sheds some light on the problem:
celldisp(out)
out{1}{1} =
246
out{2} =
Unknown
out{3}{1} =
246
I assume that I need to change the structure of out so that the contents of out{1}{1} and out{3}{1} are instead just out{1} and out{3}. But I'm not sure how to accomplish this if I need 'UniformOutput',false.
Note: I've not used MATLAB and this doesn't answer the "efficient" aspect, but...
How about forcing there to always be a match?
Just thinking about you really wanting a match to skip this problem, how about an empty match?
Looking on the MATLAB help page here I can see a 'emptymatch' option, perhaps this is something to try.
E.g.
the_thing_i_want_to_find|
Match "the_thing_i_want_to_find" or an empty match, note the | character.
In capture group it might look like this:
(the_thing_i_want_to_find|)
As a workaround, I have found that using regexprep can be used to find entries where thing3 is missing. For example:
replace='$1 ''thing3'': ''Unknown'', ''morestuff''';
missingexpr='(?<=thing2'':\s?)(''?-?[\w\d().]*?''?,) ''morestuff''';
regexprep(mycell{2},missingexpr,replace)
ans =
''thing1': '617', 'thing2': '239', 'thing3': 'Unknown', 'morestuff':, '''
Applying it to the entire array:
fixedcell=cellfun(#(x) regexprep(x,missingexpr,replace),mycell);
out=cellfun(#(x) regexp(x,expr3,'tokens','once'),fixedcell,'UniformOutput',false);
This feels a little roundabout, but it works.
cellfun can be replaced with a plain old for loop. Your code will either be equally fast, or maybe even faster. cellfun is implemented with a loop anyway, there is no advantage of using it other than fewer lines of code. In your explicit loop, you can then check the output of regexp, and build your output array any way you like.
I'm converting some Access VBA functionality to DB2 and found a vital difference. VBA lets you specify the starting point in the character string you're working on. DB2 doesn't have that option. It starts from position 1 and replaces whatever you want to be replaced in the whole string. How can I make DB2 start the replace at a specified place in the string? For example, my string is "Incongruent Plastics Incorporated" and I want to replace the second "Inc" at position 22 with "Inc". I'm doing this in a WHILE loop, going through long strings, replacing parts of them until they are less than a specified maximum (15 or 30 depending on the field).
I looked at the Locate function, but I'm not sure that's right.
Replace(a.PAYEE_STD_NAME, B.FullWord, B.abbreviation, B.mLastWord)
Where a.PAYEE_STD_NAME is the string I'm looking at, B.FullWord is what I want to replace, B.abbreviation is what I want to replace it with, and B.mLastWord is the position where I want to start replacing. Something like Replace("Incongruent Plastics Incorporated","Incorporated","Inc",22)
I expect the characters to be replaced starting in the position I need, towards the back of the string, not in the beginning.
Thanks!
Not that good at DB2, but that limitation can generally be worked around by using SUBSTR
The equivalent of Replace(a.PAYEE_STD_NAME, B.FullWord, B.abbreviation, B.mLastWord) would be:
CONCAT(SUBSTR(a.PAYEE_STD_NAME, 1, B.mLastWord - 1), Replace(SUBSTR(a.PAYEE_STD_NAME, b.mLastWord), B.FullWord, B.abbreviation))
This assumes b.mLastWord is greater than 1, if it's 1 you can use a normal REPLACE.
Maybe consider using REGEXP_REPLACE https://www.ibm.com/support/knowledgecenter/en/SSEPGG_11.1.0/com.ibm.db2.luw.sql.ref.doc/doc/r0061496.html
and possibly consider recusrive SQL rather than looping logic
I need to use the .replace() function to replace abc123="NULL" with abc123=NULL but only when NULL is the only word between the quotation marks, otherwise, leave it as it is.
Struggling to find the correct combination of escpaped characters to make this work.
Note: there are no quotation marks at the beginning or end of this data value i.e. it is not abc123="NULL" that I am working with. It is explicitly abc123="NULL"
Can any one manage this?
Edit: I'm using a privately written development environment that builds using Java.
Edit: If I could it would look like this x.replace(="NULL", =NULL) BUT I need to escape the = and quotation marks. Baring in mind I can only do this replacement if the word is NULL and is not any other word.
Not sure to well understand but, is that what you want:
var x = 'abc="NULL"';
x = x.replace('="NULL"', '=NULL');
console.log(x);
I have this piece of code that gets sessionid, make it a string, and then create a set with key as e.g. {{1401,873063,143916},<0.16443.0>} in redis. I'm trying replace { characters in this session with letter "a".
OldSessionID= io_lib:format("~p",[OldSession#session.sid]),
StringForOldSessionID = lists:flatten(OldSessionID),
ejabberd_redis:cmd([["SADD", StringForSessionID, StringForUserInfo]]);
I've tried this:
re:replace(N,"{","a",[global,{return,list}]).
Is this a good way of doing this? I read that regexp in Erlang is not a advised way of doing things.
Your solution works, and if you are comfortable with it, you should keep it.
On my side I prefer list comprehension : [case X of ${ -> $a; _ -> X end || X <- StringForOldSessionID ]. (just because I don't have to check the function documentation :o)
re:replace(N,"{","a",[global,{return,list}]).
Is this a good way of doing this? I read that regexp in Erlang is not
a advised way of doing things.
According to official documentation:
2.5 Myth: Strings are slow
Actually, string handling could be slow if done improperly. In Erlang, you'll have to think a little more about how the strings are used and choose an appropriate representation and use the re module instead of the obsolete regexp module if you are going to use regular expressions.
So, either you use re for strings, or:
leave { behind(using pattern matching)
if, say, N is {{1401,873063,143916},<0.16443.0>}, then
{{A,B,C},Pid} = N
And then format A,B,C,Pid into string.
Since Erlang OTP 20.0 you can use string:replace/3 function from string module.
string:replace/3 - replaces SearchPattern in String with Replacement. 3rd function parameter indicates whether the leading, the trailing or all encounters of SearchPattern are to be replaced.
string:replace(Input, "{", "a", all).
I have a txt file with content
$NETS
P3V3_AUX_LGATE; PQ6.8 PU37.2
U335_PIN1; R3328.1 U335.1
$END
need to be updated in this format, and save back to another txt file
$NETS
'P3V3_AUX_LGATE'; PQ6.8 PU37.2
'U335_PIN1'; R3328.1 U335.1
$END
NOTE: number of lines may go up to 10,000 lines
My current solution is to read the txt file line by line, detect the presence of the ";" and newline character and do the changes.
Right now i have a variable that holds ALL the lines, is there other way something like Replace via RegEx to do the changes without looping thru each line, this way i can readily print the result
and follow up question, which one is more efficient?
Try
ResultString = Regex.Replace(SubjectString, "^([^;\r\n]+);", "'$1';", RegexOptions.Multiline)
on your multiline string.
This will find any string (length one or more) at the start of a line up until the first semicolon if there is one and replace it with its quoted equivalent.
It should be more efficient than looping through the string line by line as you're doing now, but if you're in doubt, you'd have to profile it.
You could probably find all the matches using something like \w+; but I don't know how you'd be able to do a replace on that using Regex.Replace to add the 's but keep the original match.
However, if you already have it as one variable, you don't have to read the file again, either you could make your code find all ;s and then find the previous newline for each, or you could use a String.Split on newlines to split the variable you've already got into lines.
And if you want to get it back to one variable you can just use String.Join.
Personally I'd normally use the String.Split (and possibly the String.Join if needed) method, since I think that would make the code easy to read.
I would say Yes! this can be done with Regular expressions. Make sure you got the "multiline" option turned on and craft your regular expression using some capture groups to ease the work.
I can however say this will NOT be the optimal one. Since you mention the amount of lines you could be processing, it seems 'resource wise' smarter to use a streaming approach instead of the in memory approach.
Taking the Regex approach (and this took 15 mins so please don't think this is an optimal solution, just prove it would work)
private static Regex matcher = new Regex(#"^\$NETS\r\n(?<entrytitle>.[^;]*);\s*(?<entryrest>.*)\r\n(?<entrytitle2>.[^;]*);\s*(?<entryrest2>.*)\r\n\$END\r\n", RegexOptions.Compiled | RegexOptions.Multiline);
static void Main(string[] args)
{
string newString = matcher.Replace(ExampleFileContent, new MatchEvaluator(evaluator));
}
static string evaluator(Match m)
{
return String.Format("$NETS\r\n'{0}'; {1}\r\n'{2}'; {3}\r\n$END\r\n",
m.Groups["entrytitle"].Value,
m.Groups["entryrest"].Value,
m.Groups["entrytitle2"].Value,
m.Groups["entryrest2"].Value);
}
Hope this helps,