I have the following NSCharacterSet and want to generate a random string valid for that character set.
NSMutableCharacterSet *characterSet = [NSMutableCharacterSet alphanumericCharacterSet];
[characterSet formUnionWithCharacterSet:[NSCharacterSet whitespaceCharacterSet]];
[NSCharacterSet characterSetWithCharactersInString:] produces a character set out of a string. I want a method that does the opposite. Something like [NSString stringWithCharacterSet:]
I don't think NSCharacterSet is the best way to store the list of valid characters as it doesn't provide convenient methods to get its length or access a character at a particular index. Use NSString instead:
+ (NSString *)randomStringFromCharacters:(NSString *)chars
ofLength:(NSUInteger)length
{
unichar str[length];
for (NSUInteger i = 0; i < length; i++)
str[i] = [chars characterAtIndex:arc4random() % [chars length]];
return [NSString stringWithCharacters:str length:length];
}
Related
I'm trying to figure out the best approach to a problem. I have an essentially random alphanumeric string that I'm generating on the fly:
NSString *string = #"e04325ca24cf20ac6bd6ebf73c376b20ac57192dad83b22602264e92dac076611b51142ae12d2d92022eb2c77f";
You can see that there are no special characters, just numbers and letters, and all the letters are lowercase. Changing all the letters in this string to uppercase is easy:
[string capitalizedString];
The hard part is that I want to capitalize random characters in this string, not all of them. For example, this could be the output on one execution:
E04325cA24CF20ac6bD6eBF73C376b20Ac57192DAD83b22602264e92daC076611b51142AE12D2D92022Eb2C77F
This could be the output on another, since it's random:
e04325ca24cf20aC6bd6eBF73C376B20Ac57192DAd83b22602264E92dAC076611B51142AE12D2d92022EB2c77f
In case it makes this easier, let's say I have two variables as well:
int charsToUppercase = 12;//hardcoded value for how many characters to uppercase here
int totalChars = 90;//total string length
In this instance it would mean that 12 random characters out of the 90 in this string would be uppercased. What I've figured out so far is that I can loop through each char in the string relatively easily:
NSUInteger len = [string length];
unichar buffer[len+1];
[string getCharacters:buffer range:NSMakeRange(0, len)];
NSLog(#"loop through each char");
for(int i = 0; i < len; i++) {
NSLog(#"%C", buffer[i]);
}
Still stuck with selecting random chars in this loop to uppercase, so not all are uppercased. I'm guessing a condition in the for loop could do the trick well, given that it's random enough.
Here's one way, not particularly concerned with efficiency, but not silly efficiency-wise either: create an array characters in the original string, building an index of which ones are letters along the way...
NSString *string = #"e04325ca24cf20ac6bd6ebf73c376b20ac57192dad83b22602264e92dac076611b51142ae12d2d92022eb2c77f";
NSMutableArray *chars = [#[] mutableCopy];
NSMutableArray *letterIndexes = [#[] mutableCopy];
for (int i=0; i<string.length; i++) {
unichar ch = [string characterAtIndex:i];
// add each char as a string to a chars collection
[chars addObject:[NSString stringWithFormat:#"%c", ch]];
// record the index of letters
if ([[NSCharacterSet letterCharacterSet] characterIsMember:ch]) {
[letterIndexes addObject:#(i)];
}
}
Now, select randomly from the letterIndexes (removing them as we go) to determine which letters shall be upper case. Convert the member of the chars array at that index to uppercase...
int charsToUppercase = 12;
for (int i=0; i<charsToUppercase && letterIndexes.count; i++) {
NSInteger randomLetterIndex = arc4random_uniform((u_int32_t)(letterIndexes.count));
NSInteger indexToUpdate = [letterIndexes[randomLetterIndex] intValue];
[letterIndexes removeObjectAtIndex:randomLetterIndex];
[chars replaceObjectAtIndex:indexToUpdate withObject:[chars[indexToUpdate] uppercaseString]];
}
Notice the && check on letterIndexes.count. This guards against the condition where charsToUppercase exceeds the number of chars. The upper bound of conversions to uppercase is all of the letters in the original string.
Now all that's left is to join the chars array into a string...
NSString *result = [chars componentsJoinedByString:#""];
NSLog(#"%#", result);
EDIT Looking discussion in OP comments, you could, instead of acharsToUppercase input parameter, be given a probability of uppercase change as an input. That would compress this idea into a single loop with a little less data transformation...
NSString *string = #"e04325ca24cf20ac6bd6ebf73c376b20ac57192dad83b22602264e92dac076611b51142ae12d2d92022eb2c77f";
float upperCaseProbability = 0.5;
NSMutableString *result = [#"" mutableCopy];
for (int i=0; i<string.length; i++) {
NSString *chString = [string substringWithRange:NSMakeRange(i, 1)];
BOOL toUppercase = arc4random_uniform(1000) / 1000.0 < upperCaseProbability;
if (toUppercase) {
chString = [chString uppercaseString];
}
[result appendString:chString];
}
NSLog(#"%#", result);
However this assumes a given uppercase probability for any character, not any letter, so it won't result in a predetermined number of letters changing case.
I want to know a simple and fast way to determine if all characters in an NSString are the same.
For example:
NSString *string = "aaaaaaaaa"
=> return YES
NSString *string = "aaaaaaabb"
=> return NO
I know that I can achieve it by using a loop but my NSString is long so I prefer a shorter and simpler way.
you can use this, replace first character with null and check lenght:
-(BOOL)sameCharsInString:(NSString *)str{
if ([str length] == 0 ) return NO;
return [[str stringByReplacingOccurrencesOfString:[str substringToIndex:1] withString:#""] length] == 0 ? YES : NO;
}
Here are two possibilities that fail as quickly as possible and don't (explicitly) create copies of the original string, which should be advantageous since you said the string was large.
First, use NSScanner to repeatedly try to read the first character in the string. If the loop ends before the scanner has reached the end of the string, there are other characters present.
NSScanner * scanner = [NSScanner scannerWithString:s];
NSString * firstChar = [s substringWithRange:[s rangeOfComposedCharacterSequenceAtIndex:0]];
while( [scanner scanString:firstChar intoString:NULL] ) continue;
BOOL stringContainsOnlyOneCharacter = [scanner isAtEnd];
Regex is also a good tool for this problem, since "a character followed by any number of repetitions of that character" is in very simply expressed with a single back reference:
// Match one of any character at the start of the string,
// followed by any number of repetitions of that same character
// until the end of the string.
NSString * patt = #"^(.)\\1*$";
NSRegularExpression * regEx =
[NSRegularExpression regularExpressionWithPattern:patt
options:0
error:NULL];
NSArray * matches = [regEx matchesInString:s
options:0
range:(NSRange){0, [s length]}];
BOOL stringContainsOnlyOneCharacter = ([matches count] == 1);
Both these options correctly deal with multi-byte and composed characters; the regex version also does not require an explicit check for the empty string.
use this loop:
NSString *firstChar = [str substringWithRange:NSMakeRange(0, 1)];
for (int i = 1; i < [str length]; i++) {
NSString *ch = [str substringWithRange:NSMakeRange(i, 1)];
if(![ch isEqualToString:firstChar])
{
return NO;
}
}
return YES;
I was wondering how I would go about reversing the capitalization of the characters in an NSString or NSMutableString, ignoring non-letter characters. For example, "HeLLO jIM66" would become "hEllo Jim66".
I know about uppercaseString, lowercaseString and capitalizedString but I haven't been able to figure out how to REVERSE the capitalization of ALL the letters in the string.
Thanks for your help!
Just iterate through all of the characters in the string. If a character is uppercase, replace it with a lowercase letter; if it's lowercase, replace it with an uppercase letter; otherwise, leave it alone. For example:
+ (NSString *) reverseCase:(NSString *)str
{
int length = [str length];
NSMutableString *result = [NSMutableString stringWithCapacity:length];
for (int i = 0; i < length; i++)
{
unichar ch = [str characterAtIndex:i];
if (islower(ch))
ch = toupper(ch);
else if (isupper(ch))
ch = tolower(ch);
[result appendString:[NSString stringWithCharacters:&ch length:1]];
}
return result;
}
I'am trying to seperate a string with danish characters into a NSMutableArray. But something is not working. :(
My code:
NSString *danishString = #"æøå";
NSMutableArray *characters = [[NSMutableArray alloc] initWithCapacity:[danishString length]];
for (int i=0; i < [danishString length]; i++)
{
NSString *ichar = [NSString stringWithFormat:#"%c", [danishString characterAtIndex:i ]];
[characters addObject:ichar];
}
If I do at NSLog on the danishString it works (returns æøå);
But if I do a NSLog on the characters (the array) I get some very stange characters - What is wrong?
/Morten
First of all, your code is incorrect. characterAtIndex returns unichar, so you should use #"%C"(uppercase) as the format specifier.
Even with the correct format specifier, your code is unsafe, and strictly speaking, still incorrect, because not all unicode characters can be represented by a single unichar. You should always handle unicode strings per substring:
It's common to think of a string as a sequence of characters, but when
working with NSString objects, or with Unicode strings in general, in
most cases it is better to deal with substrings rather than with
individual characters. The reason for this is that what the user
perceives as a character in text may in many cases be represented by
multiple characters in the string.
You should definitely read String Programming Guide.
Finally, the correct code for you:
NSString *danishString = #"æøå";
NSMutableArray *characters = [[NSMutableArray alloc] initWithCapacity:[danishString length]];
[danishString enumerateSubstringsInRange:NSMakeRange(0, danishString.length) options:NSStringEnumerationByComposedCharacterSequences usingBlock:^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop) {
[characters addObject:substring];
}];
If with NSLog(#"%#", characters); you see "strange character" of the form "\Uxxxx", that's correct. It's the default stringification behavior of NSArray by description method. You can print these unicode characters one by one if you want to see the "normal characters":
for (NSString *c in characters) {
NSLog(#"%#", c);
}
In your example, ichar isn't type of NSString, but unichar. If you want NSStrings try getting a substring instead :
NSString *danishString = #"æøå";
NSMutableArray *characters = [[NSMutableArray alloc] initWithCapacity:[danishString length]];
for (int i=0; i < [danishString length]; i++)
{
NSRange r = NSMakeRange(i, 1);
NSString *ichar = [danishString substringWithRange:r];
[characters addObject:ichar];
}
You could do something like the following, which should be fine with Danish characters, but would break down if you have decomposed characters. I suggest reading the String Programming Guide for more information.
NSString *danishString = #"æøå";
NSMutableArray* characters = [NSMutableArray array];
for( int i = 0; i < [danishString length]; i++ ) {
NSString* subchar = [danishString substringWithRange:NSMakeRange(i, 1)];
if( subchar ) [characters addObject:subchar];
}
That would split the string into an array of individual characters, assuming that all the code points were composed characters.
It is printing the unicode of the characters. Anyhow, you can use the unicode (with \u) anywhere.
What's the simplest way, given a string:
NSString *str = #"Some really really long string is here and I just want the first 10 words, for example";
to result in an NSString with the first N (e.g., 10) words?
EDIT: I'd also like to make sure it doesn't fail if the str is shorter than N.
If the words are space-separated:
NSInteger nWords = 10;
NSRange wordRange = NSMakeRange(0, nWords);
NSArray *firstWords = [[str componentsSeparatedByString:#" "] subarrayWithRange:wordRange];
if you want to break on all whitespace:
NSCharacterSet *delimiterCharacterSet = [NSCharacterSet whitespaceAndNewlineCharacterSet];
NSArray *firstWords = [[str componentsSeparatedByCharactersInSet:delimiterCharacterSet] subarrayWithRange:wordRange];
Then,
NSString *result = [firstWords componentsJoinedByString:#" "];
While Barry Wark's code works well for English, it is not the preferred way to detect word breaks. Many languages, such as Chinese and Japanese, do not separate words using spaces. And German, for example, has many compounds that are difficult to separate correctly.
What you want to use is CFStringTokenizer:
CFStringRef string; // Get string from somewhere
CFLocaleRef locale = CFLocaleCopyCurrent();
CFStringTokenizerRef tokenizer = CFStringTokenizerCreate(kCFAllocatorDefault, string, CFRangeMake(0, CFStringGetLength(string)), kCFStringTokenizerUnitWord, locale);
CFStringTokenizerTokenType tokenType = kCFStringTokenizerTokenNone;
unsigned tokensFound = 0, desiredTokens = 10; // or the desired number of tokens
while(kCFStringTokenizerTokenNone != (tokenType = CFStringTokenizerAdvanceToNextToken(tokenizer)) && tokensFound < desiredTokens) {
CFRange tokenRange = CFStringTokenizerGetCurrentTokenRange(tokenizer);
CFStringRef tokenValue = CFStringCreateWithSubstring(kCFAllocatorDefault, string, tokenRange);
// Do something with the token
CFShow(tokenValue);
CFRelease(tokenValue);
++tokensFound;
}
// Clean up
CFRelease(tokenizer);
CFRelease(locale);
Based on Barry's answer, I wrote a function for the sake of this page (still giving him credit on SO)
+ (NSString*)firstWords:(NSString*)theStr howMany:(NSInteger)maxWords {
NSArray *theWords = [theStr componentsSeparatedByString:#" "];
if ([theWords count] < maxWords) {
maxWords = [theWords count];
}
NSRange wordRange = NSMakeRange(0, maxWords - 1);
NSArray *firstWords = [theWords subarrayWithRange:wordRange];
return [firstWords componentsJoinedByString:#" "];
}
Here's my solution, derived from the answers given here, for my own problem of removing the first word from a string...
NSMutableArray *words = [NSMutableArray arrayWithArray:[lowerString componentsSeparatedByString:#" "]];
[words removeObjectAtIndex:0];
return [words componentsJoinedByString:#" "];