I created an array called NSArray citiesList from a text file separating each object by the "," at the end of the line. Here is what the raw data looks like from the text file.
City:San Jose|County:Santa Clara|Pop:945942,
City:San Francisco|County:San Francisco|Pop:805235,
City:Oakland|County:Alameda|Pop:390724,
City:Fremont|County:Alameda|Pop:214089,
City:Santa Rosa|County:Sonoma|Pop:167815,
The citiesList array is fine (I can see count the objects, see the data, etc.) Now I want to parse out the city and Pop: in each of the array objects. I assume that you create a for loop to run through the objects, so if I wanted to create a mutable array called cityNames to populate just the city names into this array I would use this kind of for loop:
SMutableArray *cityNames = [NSMutableArray array];
for (NSString *i in citiesList) {
[cityNames addObject:[???]];
}
My question is what is what query should I use to find just the City: San Francisco from the objects in my array?
You can continue to use componentsSeparatedByString to divide up the sections and key/value pairs. Or you can use an NSScanner to read through the string parsing out the key/value pairs. You could use rangeOfString to find the "|" and then extract a range. So many options.
Many good suggestions in the answers here in case you really want to construct an algorithm to parse the string.
As an alternative to that, you can also look at it as a problem of declaring the structure of the data and then just have the system do the parsing. For a case like yours, regular expressions will do that nicely. Whether you prefer to do it one way or the other is largely a question of taste and coding standards.
In your specific case (if the city name is all you need to extract from the string), then also notice that there is a bit of a shortcut available that will turn it into a one-line solution: Match the whole string, define a single capture group and substitute that one to make a new string:
NSString *city = [i stringByReplacingOccurrencesOfString: #".*City:(.*?)\\|.*"
withString: #"$1"
options: NSRegularExpressionSearch
range: NSMakeRange(0, row.length)];
The variable i is the same that you have defined in your for-loop, i.e. a string containing a string representing a line in your input file:
City:San Jose|County:Santa Clara|Pop:945942,
I have added the initial .* to make the pattern robust to future new fields added to the rows. You can remove it if you don't like it.
The $1 in the substitution string represents the first capture group, i.e. the parenthesis in the regex pattern. In this specific case, the substring containing the city name. Had there been more capture groups, they would have been named $2-$9. You can check the documentation on NSRegularExpression and NSString if you want to know more.
Regular expressions are a topic all of their own, not confined to the Cocoa, although all platforms use regex implementations with their own idiosyncrasies.
You want to use componentsSeparatedByString: as below. (These lines do no error checking)
NSArray *fields = [i componentsSeparatedByString:#"|"];
NSString *city = [[[fields objectAtIndex:0] componentsSeparatedByString:#":"] objectAtIndex:1];
NSString *county = [[[fields objectAtIndex:1] componentsSeparatedByString:#":"] objectAtIndex:1];
If you can drop the keys, and a couple delimiters like this:
San Jose|Santa Clara|945942
San Francisco|San Francisco|805235
Oakland|Alameda|390724
Fremont|Alameda|214089
Santa Rosa|Sonoma|167815
Then you can simplify the code (still no error checking):
NSArray *fields = [i componentsSeparatedByString:#"|"];
NSString *city = [fields objectAtIndex:0];
NSString *county = [fields objectAtIndex:1];
for (NSString *i in citiesList) {
// Divide each city into an array, where object 0 is the name, 1 is county, 2 is pop
NSArray *stringComponents = [i componentsSeparatedByString:#"|"];
// Remove "City:" from string and add the city name to the array
NSString *cityName = [[stringComponents objectAtIndex:0] stringByReplacingCharactersInRange:NSMakeRange(0, 5) withString:#""];
[cityNames addObject:cityName];
}
Related
I have a list of contacts retrieved from Address book stored inside a MutableArray contactList. Each contact is an object which has properties like "contactName, contactImage.... etc".
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0),^{
//getAllContacts is a method which returns a Mutable array of Objects
self.contactList = [NSMutableArray arrayWithArray:[instance getAllContacts]];
//groupLetterToLoad could be "DEF"
for(int j=0; j<self.groupLetterToLoad.length;j++) {
//1st iteration D, 2nd iteration E and 3rd iteration F
NSString *testChar = [NSString stringWithFormat:#"%c",[self.groupLetterToLoad characterAtIndex:j]];
//check D,E,F with contact name property's first letter of the contact list array
for(int i=0;i<self.contactList.count;i++) {
NSString *firstChar =[[[self.contactList objectAtIndex:i] contactName] substringToIndex:1];
if([testChar isEqualToString: firstChar]) {
pos=i; //retrieve the index of the matched position
break;
}
}
if(pos!=-1) break;
}
});
Now this has two for loops (Time O(n^2)).. The disadvantage here is, if the groupLetterToLoad is "WXYZ", then comparison will start from W with A to W with Z.. How can I optimise it?
Ordering your array by contactName and performing a half interval search will reduce your complexity greatly if can avoid sorting every time you search (hint: keep [instance getAllContacts] sorted).
http://rosettacode.org/wiki/Binary_search#Objective-C - that's a starting point. you could replace the compare: with your first character comparison.
This isn't an algorithmic improvement, but the way you're handling characters is about the slowest way possible. If your group letters are really ASCII letters as you indicate, try this (I include the "if" in my answer because doing correct comparison of non-ASCII is really best left up to NSString):
1) Instead of using -substringToIndex to get the first character, use -characterAtIndex:0 and store a unichar
2) Instead of using +stringWithFormat:#"%c" to make a single character string, just use -characterAtIndex: and store it in a unichar
3) Instead of using -isEqualToString:, use == on the unichars
Unrelated, I'm pretty suspicious of the thread-safety of this. Are all those properties on self and instance you're accessing really not accessed on any other queue or thread?
I am trying to sort an iOS UITableView object. I am currently using the following code:
// Sort terms alphabetically, ignoring case
[self.termsList sortUsingSelector:#selector(localizedCaseInsensitiveCompare:)];
This sorts my list, whist ignoring case. However, it would be nice to ignore punctuation as well. For example:
c.a.t.
car
cat
should be sorted as follows:
car
c.a.t.
cat
(It doesn't actually matter which of the two cats (cat or c.a.t.) comes first, so long as they're sorted next to one another).
Is there a simple method to get around this? I presume the solution would involve extracting JUST the alphanumeric characters from the strings, then comparing those, then returning them back to their former states with the non-alphanumeric characters included again.
In point of fact, the only characters I truly care about are periods (.) but if there is a solution that covers all punctuation easily then it'd be useful to know.
Note: I asked this exact same question of Java a month ago. Now, I am creating the same solution in Objective-C. I wonder if there are any tricks available for the iOS API that make this easy...
Edit: I have tried using the following code to strip punctuation and populate another array which I sort (suggested by #tiguero). However, I don't know how to do the last step: to actually sort the first array according to the order of the second. Here is my code:
NSMutableArray *arrayWithoutPunctuation = [[NSMutableArray alloc] init];
for (NSString *item in arrayWithPunctuation)
{
// Replace hyphens/periods with spaces
item = [item stringByReplacingOccurrencesOfString:#"-" withString:#" "]; // ...hyphens
item = [item stringByReplacingOccurrencesOfString:#"." withString:#" "]; // ...periods
[arrayWithoutPunctuation addObject:item];
}
[arrayWithoutPunctuation sortUsingSelector:#selector(localizedCaseInsensitiveCompare:)];
This provides 'arrayWithoutPunctuation' which is sorted, but of course doesn't contain the punctuation. This is no good, since, although it is now sorted nicely, it no longer contains punctuation which is crucial to the array in the first place. What I need to do is sort 'arrayWithPunctuation' according to the order of 'arrayWithoutPunctuation'... Any help appreciated.
You can use a comparison block on an NSArray and your code will look like the following:
NSArray* yourStringList = [NSArray arrayWithObjects:#"c.a.t.", #"car", #"cat", nil];
NSArray* yourStringSorted = [yourStringList sortedArrayUsingComparator:^(id a, id b){
NSString* as = (NSString*)a;
NSString* bs = (NSString*)b;
NSCharacterSet *unwantedChars = [NSCharacterSet characterSetWithCharactersInString:#"\\.:',"];
//Remove unwanted chars
as = [[as componentsSeparatedByCharactersInSet: unwantedChars] componentsJoinedByString: #""];
bs = [[as componentsSeparatedByCharactersInSet: unwantedChars] componentsJoinedByString: #""];
// make the case insensitive comparison btw your two strings
return [as caseInsensitiveCompare: bs];
}];
This might not be the most efficient code actually one other option would be to iterate on your array first and remove all unwanted chars and use a selector with the caseInsensitiveCompare method:
NSString* yourStringSorted = [yourStringList sortedArrayUsingSelector:#selector(caseInsensitiveCompare:)];
This is a bit cleaner, and a bit more efficient:
NSArray* strings = #[#".....c",#"a.",#"a",#"b",#"b...",#"a..,"];
NSArray* sorted_strings = [strings sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
NSString* a = [obj1 stringByTrimmingCharactersInSet:[NSCharacterSet punctuationCharacterSet]];
NSString* b = [obj2 stringByTrimmingCharactersInSet:[NSCharacterSet punctuationCharacterSet]];
return [a caseInsensitiveCompare:b];
}];
For real efficiency, I'd write a compare method that ignores punctuation, so that no memory allocations would be needed just to compare.
My solution would be to group each string into a custom object with two properties
the original string
the string without punctuation
...and then sort the objects based on the string without punctuation.
Objective C has some handy ways to do that.
So let's say we have two strings in this object:
NSString *myString;
NSString *modified;
First, add your custom objects to an array
NSMutableArray *myStrings = [[NSMutableArray alloc] init];
[myStrings addObject: ...];
Then, sort the array by the modified variable using the handy NSSortDescriptor.
//You can specify the variable name to sort by
//Sorting is done according to the locale using localizedStandardCompare
NSSortDescriptor *mySortDescriptor = [NSSortDescriptor sortDescriptorWithKey:#"modified" ascending:YES selector:#selector(localizedStandardCompare:)];
[myStrings sortedArrayUsingDescriptors:#[ mySortDescriptor ]];
Voila! Your objects (and strings) are sorted. For more info on NSSortDescriptor...
I need to find a word or several words. With this method, however, I find also piece of word.
NSString *searchString = [NSString stringWithFormat:#"%#",searchField.text];
NSRange range = [textString rangeOfString : searchString];
if (range.location != NSNotFound) {
NSLog(#"textString = %#", textString);
}
I need the word / words exact
How can I do?
Thank you!
There are various ways of parsing/finding sub-strings in NSString:
NSString itself
NSRegularExpression. This would probably better suit your needs since you can tackle the scenario of surrounding white-spaces around words. Thus is won't return the cat from catapult when searching for cat.
NSScanner (most likely overkill for you needs)
... and they, of course, each have their PROs and CONs.
NSString has 9 methods grouped under "Finding Characters and Substrings". Methods such as:
-rangeOfString:
Finds and returns the range of the first occurrence of a given string within the receiver.
NSRegularExpression has 5 methods grouped under "Searching Strings Using Regular Expressions". Methods such as:
-numberOfMatchesInString: options: range:
Returns the number of matches of the regular expression within the specified range of the string.
It might also be useful to know about NSScanner, but this class would be more useful if you're parsing the string than simply looking for sub-parts.
What happens if you add a space at the end of the search string, like so:
NSString *searchString = [NSString stringWithFormat:#"%# ",searchField.text];
If the string from searchField.text already ends with a space, you would have to remove it.
This is not a perfect solution yet, for example you would not find the search string if it is at the end of a sentence. Instead what you could do is not adding the whitespace character, but instead look at the character after the hit and make sure that it is not a letter. For this, take a look at the class NSCharacterSet:
NSCharacterSet * letters = [NSCharacterSet letterCharacterSet];
if (![letters characterIsMember:[textString characterAtIndex:(range.location+searchString.length)]]) {
...
}
I'd like to let a string change letters to lowercase or uppercase randomly(in Xcode).
for example: "example" to "ExaMpLe" or "eXAMPle" or ExAmPlE" or something else like this randomly..
hot can i solve this?
thanks
You could either use the -uppercaseString and -lowercaseString methods on substrings, or use the toupper() and tolower() functions on characters. There's no way to simply filter a string; you'll want to use either an NSMutableString or a C array of characters.
See this question for how to get a random boolean value, which you can use to decide whether a character should be uppercase or lowercase.
NSString has both a lowercaseString and uppercaseString method. You can iterate over the characters in a string as a sequence of substrings, using some random source to call the appropriate lower/upper case on each of them, collecting the result. Something like...
NSMutableString result = [NSMutableString string];
for (NSUInteger i = 0; i < [myString length]; i++)
{
NSString *substring = [myString substringWithRange:NSMakeRange(i, 1)];
[result appendString:(rand() % 2) ? [substring lowercaseString]
: [substring uppercaseString]];
}
You may prefer a better source of entropy than rand, but it'll do for an example (don't forget to seed it if you use this case as is). If the strings are large, you can do it in-place on an NSMutableString.
You could break the word into an array of letters, and loop over this using a random number to determining case, after looping the array, simply stick the letters back together using NSMutableString.
NSString had a uppercaseString and lowercaseString methods you can use.
I have a UITextField that has data in it separated by commas (i.e, 1,2,4) I want to look at this string and extract all the numbers out of it that are separated by the commas and put it in and array. So in this example 1 2 4 would be stored in an array. Can someone help me code something like this?
Sure, no problem.
NSString *s = #"1,2,4";
NSArray *numbers = [s componentsSeparatedByString:#","];
Now you have an array of NSString objects - something like { #"1", #"2", #"4" }. You can convert those to NSNumbers or to regular integer types if you like. Here's a link to the NSString documentation for your reference.
If there's nothing else in your string of commas and digits, then you can use something like [string componentsSeparatedByString:#","]. Then you'd just need to reiterate over returned array and type-cast each element. If there's some sort of "info-noise" you may want to look into NSScanner class reference.