With GREL is it possible to get the longest string of an array ?
For example, if I have an array with 3 strings ["a","aaa","aa"], I want to obtain "aaa".
You can probably do that at the cost of a very complicated formula. It's typically to face this kind of case that Open Refine added Python (and Clojure) as scripting languages. Even if you don't know Python, you can find in two minutes the answer to the question "how to choose the longest string in list?" and simply copy and paste it (by adding a "return" instead of "print")
In this case :
return max(['a','aaa','aaaa','aa'], key=len)
EDIT
Just for the sake of the challenge, here is a possible solution with GREL.
value = "a,aa,aaaa,aa"
forEach(value.split(','), e, if(length(e)==sort(forEach(value.split(','), e, e.length()))[-1], e, null)).join(',').split(',')
Related
Let S= {a, bb, bab, abaab} is an alphabet. and kleene closure will be S* will all possible combinations.
Is string abaabbabbaab exists in S*?
what is the method to factorize to check whether it is in S* or not?
I have done it, by the following ways,
Possible factorization:
(abaab)(bab)(b)(a)(a)(b)
(abaab)(bab)(b)(aa)(b)
(abaab)(bab)(ba)(ab)
(abaab)(bab)(baa)(b)
(abaab)(bab)(b)(aab)
we can see that (abaab)(bab) is matching , but later part is not matching will combinations in S*. I have factorized the later part in many ways, but still its not matching.
I want to ask that,
is it correct?
Is this correct way to factorize(tokenize) the string?
are all factorization pairs are correct?
is this correct method to check a string whether it is belong to a
language or not?
Some of your factoriztions contain $(b)$, which is not in $S$. So they are not correct.
I think your method is exhaustive trial and error. If you do that correctly, it is a correct way to find a factorization. For checking membership of a language, it works if the language is given in the form of the Kleene closure of a finite language.
I have a test string such as: The Sun and the Moon together, forever
I want to be able to type a few characters or words and be able to match this string if the characters appear in the correct sequence together, even if there are missing words. For example, the following search word(s) should all match against this string:
The Moon
Sun tog
Tsmoon
The get ever
What regex pattern should I be using for this? I should add that the supplied test strings are going to be dynamic within an app, and so I'd like to be able to use a pattern based on the search string.
From your example Tsmoon you show partial words (T), ignoring case (s, m) and allow anything between each entered character. So as a first attempt you can:
Set the ignore case option
Between each chapter input insert the regular expression to match zero or more of anything. You can choose whether to match the shortest or longest run.
Try that, reading the documentation for NSRegularExpression if you're stuck, and see how it goes. If you get stuck ask a new question showing your code and the RE constructed and explain what happens/doesn't work as expected.
HTH
I tried to match the sql values string (0),(5),(12),... or (0,11),(122,33),(4,51),... or (0,121,12),(31,4,5),(26,227,38),... and so on with the regular expression
\(\s*\d+\s*(\s*,\s*\d+\s*)*\)(\s*,\s*\(\s*\d+\s*(\s*,\s*\d+\s*)*\))*
and it works. But...
How can I ensure that the regex does not match a values string like (0,12),(1,2,3),(56,7) with different number of columns?
Thanks in advance...
As i mentioned in comment to the question, the best way to check if input string is valid: contains the same count of numbers between brackets, is to use client side programm, but not clear SQL.
Implementation:
List<string> s = new List<string>(){
"(0),(5),(12)", "(0,11),(122,33),(4,51)",
"(0,121,12),(31,4,5),(26,227,38)","(0,12),(1,2,3),(56,7)"};
var qry = s.Select(a=>new
{
orig = a,
newst = a.Split(new string[]{"),(", "(", ")"},
StringSplitOptions.RemoveEmptyEntries)
})
.Select(a=>new
{
orig = a.orig,
isValid = (a.newst
.Sum(b=>b.Split(new char[]{','},
StringSplitOptions.RemoveEmptyEntries).Count()) %
a.newst.Count()) ==0
});
Result:
orig isValid
(0),(5),(12) True
(0,11),(122,33),(4,51) True
(0,121,12),(31,4,5),(26,227,38) True
(0,12),(1,2,3),(56,7) False
Note: The second Select statement gets the modulo of sum of comma instances and the count of items in string array returned by Split function. If the result isn't equal to zero, it means that input string is invalid.
I strongly believe there's a simplest way to achieve that, but - at this moment - i don't know how ;)
:(
Unless you add some more constraints, I don't think you can solve this problem only with regular expressions.
It isn't able to solve all of your string problems, just as it cannot be used to check that the opening and closing of brackets (like "((())()(()(())))") is invalid. That's a more complicated issue.
That's what I learnt in class :P If someone knows a way then that'd be sweet!
I'm sorry, I spent a bit of time looking into how we could turn this string into an array and do more work to it with SQL but built in functionality is lacking and the solution would end up being very hacky.
I'd recommend trying to handle this situation differently as large scale string computation isn't the best way to go if your database is to gradually fill up.
A combination of client and serverside validation can be used to help prevent bad data (like the ones with more numbers) from getting into the database.
If you need to keep those numbers then you could rework your schema to include some metadata which you can use in your queries, like how many numbers there are and whether it all matches nicely. This information can be computed inexpensively from your server and provided to the database.
Good luck!
I'm on OS X, and in objective-c I'm trying to convert
for example,
"Bobateagreenapple"
into
"Bob ate a green apple"
Is there any way to do this efficiently? Would something involving a spell checker work?
EDIT: Just some extra information:
I'm attempting to build something that takes some misformatted text (for example, text copy pasted from old pdfs that end up without spaces, especially from internet archives like JSTOR). Since the misformatted text is probably going to be long... well, I'm just trying to figure out whether this is feasibly possible before I actually attempt to actually write system only to find out it takes 2 hours to fix a paragraph of text.
One possibility, which I will describe this in a non-OS specific manner, is to perform a search through all the possible words that make up the collection of letters.
Basically you chop off the first letter of your letter collection and add it to the current word you are forming. If it makes a word (eg dictionary lookup) then add it to the current sentence. If you manage to use up all the letters in your collection and form words out of all of them, then you have a full sentence. But, you don't have to stop here. Instead, you keep running, and eventually you will produce all possible sentences.
Pseudo-code would look something like this:
FindWords(vector<Sentence> sentences, Sentence s, Word w, Letters l)
{
if (l.empty() and w.empty())
add s to sentences;
return;
if (l.empty())
return;
add first letter from l to w;
if w in dictionary
{
add w to s;
FindWords(sentences, s, empty word, l)
remove w from s
}
FindWords(sentences, s, w, l)
put last letter from w back onto l
}
There are, of course, a number of optimizations you could perform to make it go fast. For instance checking if the word is the stem of any word in the dictionary. But, this is the basic approach that will give you all possible sentences.
Solving this problem is much harder than anything you'll find in a framework. Notice that even in your example, there are other "solutions": "Bob a tea green apple," for one.
A very naive (and not very functional) approach might be to use a spell-checker to try to isolate one "real word" at a time in the string; of course, in this example, that would only work because "Bob" happens to be an English word.
This is not to say that there is no way to accomplish what you want, but the way you phrase this question indicates to me that it might be a lot more complicated than what you're expecting. Maybe someone can give you an acceptable solution, but I bet they'll need to know a lot more about what exactly you're trying to do.
Edit: in response to your edit, it would probably take less effort to run some kind of OCR tool on a PDF and correct its output than it would just to correct what this system might give you, let alone program it
I implemented a solution, the code is avaible on code project:
http://www.codeproject.com/Tips/704003/How-to-add-spaces-between-spaceless-strings
My idea was to prioritize results that use up most of the characters (preferable all of them) then favor the ones with the longest words, because 2,3 or 4 character long words can often come up by chance from leftout characters. Most of the times this provides the correct solution.
To find all possible permutations I used recursion. The code is quite fast even with big dictionaries (tested with 50 000 words).
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
String vs StringBuilder
I just revisited some of the books that I used to pick up VB.NET. I am not sure I've got this in my head, understand how/what StringBuilder is.
What is the guidance for using? Is it best to use it if you are are concatenating 2 strings or 50?
Or when the the total string length is greater than 128 characters?
Or will you see a performance benefit whenever you use it to add strings together?
In which case is it better to use a StringBuilder instance to build a SQL statement than string.format("Select * from x where y = {0}",1)?
It's always struck me that declaring another variable and including a name space is not beneficial for small string concatenations, but I am not sure now.
Sorry, lot of documentation tells you what to use, just not what's best.
I've got an article on this very topic. In summary (copied from the bottom of the page):
Definitely use StringBuilder when you're concatenating in a non-trivial loop - especially if you don't know for sure (at compile time) how many iterations you'll make through the loop. For example, reading a file a character at a time, building up a string as you go using the += operator is potentially performance suicide.
Definitely use the concatenation operator when you can (readably) specify everything which needs to be concatenated in one statement. (If you have an array of things to concatenate, consider calling String.Concat explicitly - or String.Join if you need a delimiter.)
Don't be afraid to break literals up into several concatenated bits - the result will be the same. You can aid readability by breaking a long literal into several lines, for instance, with no harm to performance.
If you need the intermediate results of the concatenation for something other than feeding the next iteration of concatenation, StringBuilder isn't going to help you. For instance, if you build up a full name from a first name and a last name, and then add a third piece of information (the nickname, maybe) to the end, you'll only benefit from using StringBuilder if you don't need the (first name + last name) string for other purpose (as we do in the example which creates a Person object).
If you just have a few concatenations to do, and you really want to do them in separate statements, it doesn't really matter which way you go. Which way is more efficient will depend on the number of concatenations the sizes of string involved, and what order they're concatenated in. If you really believe that piece of code to be a performance bottleneck, profile or benchmark it both ways.
Here is my rule of thumb:
StringBuilder is best used when the exact number of concatenations is unknown at compile time.
Coding Horror has a good article concerning this question, The Sad Tragedy of Micro-Optimization Theater.
Personally I use StringBuilder when I have more than just one or two strings to concatenate. I'm not sure if there's a real performance hit to be gained, but I've always read and been told that doing a regular concatenation with multiple strings creates an extra copy of the string each time you do it, while using StringBuilder keeps one copy until you call the final ToString() method on it.
Someone's figured out experimentally that the critical number is 6. More than 6 concatenations in a row and you should use a StringBuilder. Can't remember where I found this.
However, note that if you just write this in a line:
"qwert" + "yuiop" + "asdf" + "gh" + "jkl;" + "zxcv" + "bnm" + ",."
That gets converted into one function call (I don't know how to write it in VB.net)
String.Concat("qwert", "yuiop", "asdf", "gh", "jkl;", "zxcv", "bnm", ",.");
So if you're doing all concatenations on one line, then don't bother with StringBuilder because String.Concat effectively will do all the concatenations in one go. It's only if you're doing them in a loop or successively concatenating.
My rule - when you're adding to a string in a For or Foreach loop, use the StringBuilder.