I need to scroll through several thousands of words to categorize them... to determine which words have the same pattern. (this part works)
For example, a four letter word that has two m's in 2nd & 4th position represent a pattern ("-m-m"). Once I have gone through all the words, I will know how many words there are for any given pattern. I am scrolling through now, but the problem I have is 'remembering' how many words I have in any given pattern.
I was thinking of using NSMutableDictionary and have the key be the pattern ('-m-m-') and the object represent the count of that pattern. This means every time I come across a pattern, I look up that pattern in the dictionary, get the key, increment the key, and put it back in the dictionary.
I need help with both the decision and syntax for performing this task.
Thank You
The answer to your question was this part of your (given) question "I will know how many words there are for any given pattern.". I would use an array of dictionary. You use the dictionary to store key value pair: a known pattern and the count. And you use the array to store those KVP records. So the next time you detect a pattern, search for the array for that record (dictionary), if found, increment the count. If not, create new record and set the count to 1.
Added sample code:
#define kPattern #"Pattern"
#define kPatternCount #"PatternCount"
-(NSMutableDictionary *)createANewDictionaryRecord:(NSString *) newPattern
{
int count = 1;
NSMutableDictionary *myDictionary = [NSMutableDictionary dictionaryWithObjectsAndKeys:
newPattern, kPattern,
[NSString stringWithFormat:#"%i",count], kPatternCount,
nil];
return myDictionary;
}
-(void)addANewPatternToArray:(NSMutableDictionary *)newDictionary
{
// NSMutableArray *myArrayOfDictionary = [[NSMutableArray alloc]init]; // you need to define it somewhere else and use property etc.
[self.myArrayOfDictionary addObject:newDictionary]; //or [self.myArrayOfDictionary addObject:newDictionary]; if you follow the recommendation above.
}
-(BOOL)existingPatternLookup:(NSString *)pattern
{
for (NSMutableDictionary *obj in self.myArrayOfDictionary)
{
if ([[obj objectForKey:kPattern] isEqual:pattern])
{
int count = [[obj objectForKey:kPatternCount] intValue] + 1;
[obj setValue:[NSString stringWithFormat:#"%i",count] forKey:kPatternCount];
return YES;
}
}
[self.myArrayOfDictionary addObject:[self createANewDictionaryRecord:pattern]];
return NO;
}
-(void)testData
{
NSMutableDictionary *newDict = [self createANewDictionaryRecord:#"mmm"];
[self addANewPatternToArray:newDict];
}
-(void) printArray
{
for (NSMutableDictionary * obj in self.myArrayOfDictionary)
{
NSLog(#"mydictionary: %#", obj);
}
}
- (IBAction)buttonPressed:(id)sender
{
if ([self existingPatternLookup:#"abc"])
{
[self printArray];
} else
{
[self printArray];
}
}
Not being an objective C expert but solving this problem in java before, I would say a dictionary(I used a map when doing it in java) is the best way. Check if the key(pattern) already exist if so increment that count else put a new one in the dictionary.
EDIT
If you want to not just get the count of a pattern, but in fact tell which words fall under that pattern, I would use a dictionary of strings to mutable arrays. In the arrays you store the words and the key to the array is the pattern(as a string), similar code as above but instead of just incrementing the count, you have to add the new word to the array.
The only difference in NSDictionary and NSMutableDictionary is that one can have objects added to it. I think your implementation is good, but English is a complex language. It would be more efficient to parse out the string with regex than to set a key for it.
Why don't you use NSCountedSet instead:
NSCountedSet Class Reference
..which is available in iOS 2.0 and later?
Each distinct object inserted into an NSCountedSet object has a counter associated with it. NSCountedSetkeeps track of the number of times objects are inserted [...] Thus, there is only one instance of an object in an NSSet object even if the object has been added to the set multiple times. The count method defined by the superclass NSSet has special significance; it returns the number of distinct objects, not the total number of times objects are represented in the set.
Then use:
- (NSUInteger)countForObject:(id)anObject
Use a dictionary of NSMutableArrays, and check for the existence of each search key as you recommended. If the key doesn't exist, add an NSMutableSet or NSMutableArray (depending on your needs) for the searched key type "-m-m" for example, and then add to the set or array for that key.
Related
Sorry guys, this problem I am running into is pretty trivial. I just can't wrap my head around it so hope someone can help me. Your help is really appreciated. I am getting JSON data through NSURLConnectDelegate with a web API. I get something like this back:
(
{
id = 340
name = Vicent },
{
id = 339
name = Johny },
{
id = 338
name = Eric }
)
and I save it in a NSMutableArray as a global variable. Now, I have a NSSet of "ids". For example:
{
340, 339
}
In the numberOfRowsInSection, I return the set's count. I am trying to load only the ids in the NSSet from the array with the data saved from the webAPI, so I do something like this in cellForRowIndexPath:
for (NSNumber *num in [set allObjects]) {
NSString *newString = [[savedArray objectAtIndex:indexPath.row]
NSString *new = [num stringValue];
if ([new isEqual:newString]) {
}}
How can I just populate the ids I want?
The JSON makes it look like you have an array of dictionaries, which is a reasonable data structure to use as the data source for a table view.
It sounds like you're trying to filter your array to only include the items that are in your set. Is that right?
If so, you could write code that would create a new array containing the subset of your array elements who's ID is also in your set. There are at least a half-dozen ways to do that. One fairly simple approach would be to use the NSArray method indexesOfObjectsPassingTest. You'd pass that method a block of code that would check each array element to see if it's id object was in your set.
That would give you an NSIndexSet with the indexes of the items in your array who's ID are in your set. Then you could use the NSArray method objectsAtIndexes to get an array of only the objects that are also in the set. Something like this (Assuming that your array of dictionaries is called savedArray and your set is called allObjects:
//get the indexes of items in the array savedArray who's id appears in the set allObjects
NSIndexSet *indexes = [savedArray indexesOfObjectsPassingTest:
^(NSDictionary *obj,
NSUInteger idx,
BOOL *stop)
{
return [allObjects member: obj[#"id"]] != nil;
}
];
//Now build an (immutable) array of just the objects who's ID are in the set
NSArray *subArray = [savedArray objectsAtIndexes: indexes];
The array subArray created above is immutable. If you need a mutable array you would need to make a mutable copy, which is a one-line change.
Disclaimer: I still struggle a little with block syntax, so the above might not be exactly correct, but it gives you the general idea.
I have an NSArray filled with only NSStrings
I understand that to iterate over a NSArray of n elements, all I have to do is use for (NSString *element in arrayOfElements). However, I was wondering if there is specific function that will perform a comparison between every string element in the array with each other. For example, if I have the array:
[#"apple", #"banana", #"peach", #"kiwi"],
how would I do the comparison so apple is compared to banana, peach and then kiwi; and then banana is against peach and wiki, and finally peach is against kiwi?
Try using nested for loops, ex:
for (int i = 0 ; i < array.count ; i ++) {
for (int j = i + 1 ; j < array.count ; j ++) {
// compare array[i] to array [j]
}
}
Edit: And although wottle's suggestion would work, I'd recommend mine in this case, since it won't waste iterations going over the same comparisons multiple times. What I've done in this algorithm by setting j = i + 1 is compare each element in the array only to the ones after it.
Given "the array will not have any duplicates, and every NSString will be unique" this sounds like a great case for using NSSet classes instead of NSArray. NSMutableSet provides:
minusSet:
Removes each object in another given set from the receiving
set, if present.
and
intersectSet:
Removes from the receiving set each object that isn’t a
member of another given set.
I'm not sure which operation you're looking for but it sounds like one of those should cover your exact use case.
What you're trying to do is a bit beyond what custom comparators were meant to do. Typically when you have a list and you want to run a custom comparator, you're doing it to sort the list. You seem to want to do some specific action when certain items in the list compare to others, and for that, I think a loop within a loop is your best bet. It won't be very good performance, so hopefully you are not expecting a large array:
-(void) compareArrayToSelf
{
NSArray *array=#[#"apple", #"bananna", #"peach", #"kiwi"];
for( NSString *value1 in array)
{
for( NSString *value2 in array)
{
if( ![value1 isEqualToString:value2] && [self compareArrayValue:value1 toOtherValue:value2])
{
//Do something with either value1 or value2
}
}
}
}
I'm trying to access every name in the beers array for a search algorithm. I have the array set up as a dictionary,but it doesn't behave quite like a dictionary. Here is what the data looks like:
Just so you can see how I've been accessing the array, here is how I populated my uitableview.So, basically I know how to access individual objects in the arrray but I can't access the whole array. :
cell.detailTextLabel.text=[self.beers[indexPath.row] name]
Then again I might be totally off base. I'm still learning objective c and ios here so sorry if my inexperience shows through in my post. any tips help. Thanks guys!
I'm assuming that you want a new array that contains just the names of each Beer object and not the object itself. You can use an array "mapping" function like in this category.
typedef id(^MapBlock)(id input);
#implementation NSArray (Additions)
- (NSArray *)arrayByMappingWithBlock:(MapBlock)block {
NSMutableArray *array = [[NSMutableArray alloc] initWithCapacity:self.count];
for (id obj in self) {
[array addObject:block(obj)];
}
return array;
}
#end
You would then use it like so...
NSArray *beerNames = [self.beers arrayByMappingWithBlock:^id(Beer *beer) {
return beer.name;
}];
Not really sure if that is what you want to achieve, but the following line will produce an array containing all beer names:
[self.beers valueForKeyPath:#"name"];
You can access all of the names in the array by iterating through the array with a loop
for ( Beer *beer in self.beers )
NSLog( #"%#", beer.name );
I have a generic person object with properties personName, lastName, and age. I am storing the user input into an NSMutableArray and I wanted to find a under by his/her name in the array. I have tried finding a bunch of different solutions but none that quite really work.
This is my main.m
#autoreleasepool {
char answer;
char locatePerson[40];
//Create mutable array to add users for retrieval later
NSMutableArray *people = [[NSMutableArray alloc] init];
do{
Person *newPerson = [[Person alloc]init];
[newPerson enterInfo];
[newPerson printInfo];
[people addObject:newPerson];
NSLog(#"Would you like to enter another name?");
scanf("\n%c", &answer);
}while (answer == 'y');
NSLog(#"Are you looking for a specific person?");
scanf("%c", locatePerson);
//This is where I need help
int idx = [people indexOfObject:]
}
This is very basic but I am new to objective-c and I wanted to try and find the user by name. The solutions I've seen have used the indexesOfObjectsPassingTest method. But I was wondering if I can't just use the indexOfObjectmethod the way I did there to locate a person by its name?
Any help is appreciated.
This is one of those hard problems you should avoid with some up-front design. If you know that you are putting things into a collection class and will need to get them out again based on some attribute (rather than by order of insertion) a dictionary is the most efficient collection class.
You can use a NSDictionary keyed with Person's name attribute. You can still iterate over all the objects but you will avoid having to search the whole collection. It can take a surprisingly long time to find a matching attribute in a NSArray! You wouldn't even have to change your Person object, just do
NSDictionary *peopleDictionary = #{ person1.name : person1, person2.name : person2 };
or add them one by one as they are created into a NSMutableArray.
You can try something like this assuming that 'name' is a property for your Person class.
NSUInteger i = 0;
for(Person *person in people) {
if([person.name isEqualToString:locatePerson]) {
break;
}
i++;
}
I am creating some XML in objective C, I know how to do it however there is the possibility that there could be 800+ values I might be putting into XML, which I am getting from a NSArray of NSDictionaries.
So I was wondering if there is an efficient way of checking for nill or null in a keyvalue that's of type NSString.
Currently this is what my code looks like:
NSMutableArray *xmlItems = [coreDataController readInstallForXML:selectedInstallID];
for (int i = 0; i < [xmlItems count]; i++) {
NSDictionary *currentXMLItem = [xmlItems objectAtIndex:i];
[xmlWriter writeStartElement:#"Items"];
[xmlWriter writeAttribute:#"insID" value:[currentXMLItem valueForKey:#"insID"]];
// there are about another 20 attributes I have to add here.
}
// then write end elemtent etc.
In the code above I have no added any checking but I was hoping someone might have something better for me than adding a bunch of if statements for each attribute.
You can use [NSDictionary allKeysForObject:] to get all keys for the 'nil' values, so you have a list of keys to ignore.
Generating 800 items is not necessarily 'much' or 'slow'. You don't want to do that on the main thread anyway, so just make sure you perform it as a background operation.
use the allKeys method on the NSDictionary to return an NSArray of keys; then iterate through that array and for each key retrieve the value from the dictionary and use one if statement to check the string before writing out the xml element