I'm analyzing a file in matlab and I want to find the number of occurrences of the letter I (capitalized). I'm confused on how to write the regular expression for this step. Would it be something like (lines,'.I.')? Any help would be greatly appreciated.
If you want to count the number of capital 'I's in a file, assuming you have read the file in as a string, you could just do this:
count = sum(file_string == 'I');
If, as in this case, the file is read into a cell-string, one possible way of doing this would be to use:
count = sum(strcat(file_cellstr{:}) == 'I');
strcat will concatenate all of the strings passed to it into a single string. Passing file_cellstr{:} to strcat is essentially concatenating each of the cells (i.e. each line in your case) into a single string, then searching through it for the letter 'I'. If you wanted to find a whole word, you could use
count = length(strfind(strcat(file_cellstr{:}),'word'));
If you wanted a regular expression match, you could do the following:
count = length(regexp(strcat(file_cellstr{:}),'[a-z]+'));
Related
I have a string, and I want to extract, using regular expressions, groups of characters that are between the character : and the other character /.
typically, here is a string example I'm getting:
'abcd:45.72643,4.91203/Rou:hereanotherdata/defgh'
and so, I want to retrieved, 45.72643,4.91203 and also hereanotherdata
As they are both between characters : and /.
I tried with this syntax in a easier string where there is only 1 time the pattern,
[tt]=regexp(str,':(\w.*)/','match')
tt = ':45.72643,4.91203/'
but it works only if the pattern happens once. If I use it in string containing multiples times the pattern, I get all the string between the first : and the last /.
How can I mention that the pattern will occur multiple time, and how can I retrieve it?
Use lookaround and a lazy quantifier:
regexp(str, '(?<=:).+?(?=/)', 'match')
Example (Matlab R2016b):
>> str = 'abcd:45.72643,4.91203/Rou:hereanotherdata/defgh';
>> result = regexp(str, '(?<=:).+?(?=/)', 'match')
result =
1×2 cell array
'45.72643,4.91203' 'hereanotherdata'
In most languages this is hard to do with a single regexp. Ultimately you'll only ever get back the one string, and you want to get back multiple strings.
I've never used Matlab, so it may be possible in that language, but based on other languages, this is how I'd approach it...
I can't give you the exact code, but a search indicates that in Matlab there is a function called strsplit, example...
C = strsplit(data,':')
That should will break your original string up into an array of strings, using the ":" as the break point. You can then ignore the first array index (as it contains text before a ":"), loop the rest of the array and regexp to extract everything that comes before a "/".
So for instance...
'abcd:45.72643,4.91203/Rou:hereanotherdata/defgh'
Breaks down into an array with parts...
1 - 'abcd'
2 - '45.72643,4.91203/Rou'
3 - 'hereanotherdata/defgh'
Then Ignore 1, and extract everything before the "/" in 2 and 3.
As John Mawer and Adriaan mentioned, strsplit is a good place to start with. You can use it for both ':' and '/', but then you will not be able to determine where each of them started. If you do it with strsplit twice, you can know where the ':' starts :
A='abcd:45.72643,4.91203/Rou:hereanotherdata/defgh';
B=cellfun(#(x) strsplit(x,'/'),strsplit(A,':'),'uniformoutput',0);
Now B has cells that start with ':', and has two cells in each cell that contain '/' also. You can extract it with checking where B has more than one cell, and take the first of each of them:
C=cellfun(#(x) x{1},B(cellfun('length',B)>1),'uniformoutput',0)
C =
1×2 cell array
'45.72643,4.91203' 'hereanotherdata'
Starting in 16b you can use extractBetween:
>> str = 'abcd:45.72643,4.91203/Rou:hereanotherdata/defgh';
>> result = extractBetween(str,':','/')
result =
2×1 cell array
{'45.72643,4.91203'}
{'hereanotherdata' }
If all your text elements have the same number of delimiters this can be vectorized too.
I am trying to add a new calculated column that counts the number of semi colons in a string and adds one to it. So the column i have contains a bunch of aliases and I need to know how many for each row.
For example,
A; B; C; D
So basically this means there are 4 aliases (3 semi colons + 1)
Need to do this for over 2 million rows. Help please!
Basic idea is to subtract length of your string without ; characters from it's original length:
len([columnName])-len(Substitute([columnName],";",""))+1
Here it is with a regular expression:
Len(RXReplace([Column 1], "(?!;).", "", "gis"))+1
RXReplace takes as arguments:
The string you are wanting to work on (in this case it is on Column 1)
The regular expression you want to use (here it is (?!;). )
What you want to replace matches with (blank in this situation so
that everything that matches the regex is removed)
Finally a parameter saying how you want it to work (we are passing
in gis which means replace all matches not just the first, ignore case, replace newlines)
We wrap this in a Len which gives us the amount of semicolons since that is all that is left and finally we add 1 to it to get the final result.
You can read more about the regular expression here: https://msdn.microsoft.com/en-us/library/az24scfc(v=vs.110).aspx but in a nutshell it says match everything that isn't a semi colon.
You can read more about RXReplace and Len here: https://docs.tibco.com/pub/spotfire/6.0.0-november-2013/userguide-webhelp/ncfe/ncfe_text_functions.htm
I have a series of strings in a cvs file, they all look like the two bellow:
7336598,"[4125420656L, 2428145712L, 1820029797L, 1501679119L, 1980837904L, 380501274L]"
7514340,"[507707719L, 901144614L, 854823005L]"
....
how can I extract the numbers in it?
As in.. to retreive 7336598, 4125420656, etc....
Tried textscan, and regexp, but not much success...
Sorry for the beginners question...and thank you for having a look! :)
Edit: the size of each line is variable.
You can use textread and regexp to extract only the numbers from your CSV file:
C = textread('file.cvs', '%s', 'delimiter', '\n');
C = regexp(C, '\d+', 'match');
The regular expression is quite simple. In MATLAB's regexp pattern,\d denotes a digit, and the + indicates that this digit must occur at least once. The match mode tells regexp to return the matched strings.
The result is a cell array of strings. You can go further and convert the strings to numerical values:
C = cellfun(#(x)str2num(sprintf('%s ', x{:})), C, 'Uniform', false)
The result is still stored in a cell array. If you can guarantee that there's the same amount of numerical values in each row, you can convert the cell array to a matrix:
A = cell2mat(C);
I don't have matlab to test, but does a '[0-9]+' does the job ?
It works for me outside matlab :
echo '7336598,"[4125420656L, 2428145712L, 1820029797L, 1501679119L, 1980837904L, 380501274L]"' | grep -o '[0-9]\+'
7336598
4125420656
2428145712
1820029797
1501679119
1980837904
380501274
I want to matching of filenames like Colibri does. I tried to solve it by regular expressions.
Searching in Colibri works that You type characters which are in order inside of a filename and it finds all files with these characters in order in the filename. For example for "ab" it finds "cabal", "ab", and "achab".
Simple insertion of .* between letters works (so searched string "ab" becomes regular expression .*a.*b.*), but I want to make it on large amount of files.
So far I have O(N*???), where N is amount of filenames and ??? is at best linear complexity (I assume my language uses NFA). I don't care about space complexity that much. What data structures or algorithms should I choose to make it more efficient (in time complexity)?
If you just want to check whether the characters of a search string search are contained in another string str in the same order, you could use this simple algorithm:
pos := -1
for each character in search do
pos := indexOf(str, character, pos+1)
if pos is -1 then
break
endif
endfor
return pos
This algorithm returns the offset of the last character of search in str and -1 otherwise. Its runtime is in O(n) (you could replace indexOf by a simple while loop that compares the characters in str from pos to Length(str)-1 and returns either the offset or -1).
It will greatly improve your efficiency if you replace the . with a character negation. i.e.
[^a]*a[^b]*b.*
This way you have much less backtracking. See This Reference
Edit* #yi_H you are right, this regex would probably serve just as well:
a[^b]*b
Your . is unnecessary. You'll get better performance if you simply transform "abc"
into ^[^a]*a[^b]*b[^c]*c.
string exp = "^";
foreach (char c in inputString)
{
string s = Regex.Escape (c.ToString()); // escape `.` as `\.`
exp += "[^" + s + "]*" + s; // replace `a` with `[^a]*a`
}
Regex regex = new Regex (exp, RegexOptions.IgnoreCase);
foreach (string fileName in fileNames)
{
if (regex.IsMatch (fileName))
yield return fileName;
}
For a limited character-set it might make sense to create lookup table which contains an array or linked list of matching filenames.
If your ABC contains X characters then the "1 length" lookup table will contain X table entries, if it is a "2 length" table it will contain X^2 entries and so on. The 2 length table will contain for each entry ("ab", "qx") all the files which which have those letters in that order. When searching for longer input "string" look up the appropriate entry and do the search on those entries.
Note: calculate the needed extra memory and measure the speed improvement (compared to full table scan), the benefits depend on the data set.
Say I have a CString object strMain="AAAABBCCCCCCDDBBCCCCCCDDDAA";
I also have two smaller strings, say strSmall1="BB";
strSmall2="DD";
Now, I want to replace all occurence of strings which occur between strSmall1("BB") and strSmall2("DD") in strMain, with say "KKKKKKK"
Is there a way to do it without Regex. I cannot use regex as adding another file to the project is prohibited.
Is there a way in VC++/MFC to do it? Or any easy algorithm you can point me to?
int length = strMain.GetLength();
int begin = strMain.Find(strSmall1, 0) + strSmall1.GetLength();
int end = strMain.Find(strSmall2, 0);
CStringT left = strMain.Left(begin);
CStringT right = strMain.Right(length - end);
strMain = left + "KKKKKKK" + right
The easiest way is probably to handle the replacement recursively. Search for the starting delimiter and the ending delimiter. If you find them, put together a new string consisting of the string up to the starting delimiter, followed by the replacement string, followed by the return from recursively doing the replacement in the remainder of the string following the ending delimiter.
That, of course, assumes you want to replace all the occurrences in the main string -- if you only want to replace the first one, John Weldon's solution (for one example) will work quite nicely.
psudocode:
loop over string
if curlocation matches string strsmall1 save index break
loop over remaining string
replace till curlocation matches string strsmall2
Extra credit:
What will the next assignment be?
My answer:
Speed it up by jumping the length of strsmall1 and strsmall2 in loop iterations