How do I count the occurrences of ALL characters of a string? - ios

Question

I am trying to find the number of times each character in a string is used. for example, in the string "wow" I would like to count the number of times the character "w" is used and the number of times the character "o" is used. I would then like to add these characters to an NSMutableArray. Is there a programmatic way to count the number of times all specific characters are used? To get the number of occurrences of ALL characters in an NSString? Or would I have to go through the process of counting the occurrences of each individual character separately?

Answer 1

See iOS - Most efficient way to find word occurrence count in a string
NSString *string = #"wow";
NSCountedSet *countedSet = [NSCountedSet new];
[string enumerateSubstringsInRange:NSMakeRange(0, [string length])
options:NSStringEnumerationByComposedCharacterSequences | NSStringEnumerationLocalized
usingBlock:^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop){
// This block is called once for each word in the string.
[countedSet addObject:substring];
// If you want to ignore case, so that "this" and "This"
// are counted the same, use this line instead to convert
// each word to lowercase first:
// [countedSet addObject:[substring lowercaseString]];
}];
NSLog(#"%#", countedSet);
NSLog(#"%#", [countedSet allObjects]);
NSLog(#"%d", [countedSet countForObject:#"w"]);

Answer 2

The exact answer depends on some questions -
Do you only want to count the characters a-z or do you want punctuation as well?
Do you need to count unicode characters or just 8 bit characters?
Is case important ie. is A different to a?
Assuming you only want to count 8 bit, a-z independent of case, you could use something like -
- (NSArray *)countCharactersInString:(NSString *)inputString
{
NSMutableArray *result=[[NSMutableArray alloc]initWithCapacity:26];
for (int i=0;i<26;i++) {
[result addObject:[NSNumber numberWithInt:0]];
}
for (int i=0;i<[inputString length];i++)
{
unichar c=[inputString characterAtIndex:i];
c=tolower(c);
if (isalpha(c))
{
int index=c-'a';
NSNumber *count=[result objectAtIndex:index];
[result setObject:[NSNumber numberWithInt:[count intValue]+1] atIndexedSubscript:index];
}
}
return (result);
}
An alternative approach is to use an NSCountedSet - it handles all characterspunctuation etc, but will be 'sparse' - there is no entry for a character that is not present in the string. Also, the implementation below is case sensitive - W is different to w.
- (NSCountedSet *)countCharactersInString:(NSString *)inputString
{
NSCountedSet *result=[[NSCountedSet alloc]init];
for (int i=0;i<[inputString length];i++)
{
NSString *c=[inputString substringWithRange:NSMakeRange(i,1)];
[result addObject:c];
}
return result;
}

Answer 3

NSString *str = #"Program to Find the Frequency of Characters in a String";
NSMutableDictionary *frequencies = [[NSMutableDictionary alloc]initWithCapacity:52];
initWithCapacity:52 - capacity can be more depends on character set (for now : a-z, A-Z)
for (short i=0; i< [str length]; i++){
short index = [str characterAtIndex:i];
NSString *key = [NSString stringWithFormat:#"%d",index];
NSNumber *value = #1;
short frequencyCount=0;
if ([frequencies count] > 0 && [frequencies valueForKey:key]){
frequencyCount = [[frequencies valueForKey:key] shortValue];
frequencyCount++;
value = [NSNumber numberWithShort:frequencyCount];
[frequencies setValue:value forKey:key];
}
else{
[frequencies setValue:value forKey:key];
}
}
To display occurrence of each character in string
[frequencies enumerateKeysAndObjectsUsingBlock:^(id _Nonnull key, id _Nonnull obj, BOOL * _Nonnull stop) {
NSString *ky = (NSString*)key;
NSNumber *value = (NSNumber*)obj;
NSLog(#"%c\t%d", ([ky intValue]), [value shortValue]);
}];