I am using this code in a loop to populate an NSMutable Array of NSMutableSets (of NSString objects). The index of the NSSet is based on the length of the word.
// if set of this length not initialized yet, initialize set.
wordIndex = [NSString stringWithFormat:#"%d", currentWordLength];
if ([myWordArray objectForKey:wordIndex] == nil)
[myWordArray setObject:[[NSMutableSet alloc] initWithObjects:currentWord, nil] forKey:wordIndex];
else
[[myWordArray objectForKey:wordIndex] addObject:currentWord];
The final intention is to split up an array of words into an array of sets of words grouped by their lengths.
However, I see that [myWordArray count] is 0 after this. Why?
You are confusing the methods of NSMutableDictionary and NSMutableArray: In Objective-C arrays do not have keys but have indexes. If you change the class for myWordArray to NSMutableDicitionary it should work.
Try this, it looks very much like your logic, but (1) it uses NSNumbers as keys, which makes a little more sense, (2) handles the missing set condition more simply, but just adding the set, and (3) breaks up the source lines somewhat for easier debugging...
NSArray *inputStrings = // however these are initialized goes here
NSMutableDictionary *result = [NSMutableDictionary dictionary];
for (NSString *currentString in inputStrings) {
NSInteger currentWordLength = currentString.length;
wordIndex = [NSNumber numberWithInt:currentWordLength];
NSMutableSet *wordSet = [result objectForKey:wordIndex];
if (!wordSet) {
wordSet = [NSMutableSet set];
[result setObject:wordSet forKey:wordIndex];
}
[wordSet addObject:currentWord];
}
If you still have an empty dictionary after running this, it might be simpler to watch what's happening by stepping through it.
Related
I have this snipped of code that results in an array with a whole bunch of "<null>" throughout and I need to figure out how to remove them. Obviously after smashing my head against the keyboard I'm asking for some help.
In my .h I have declared:
NSArray *sortedContacts;
NSArray *rawContacts;
And then in .m:
-(void) buildContacts {
ABAddressBook *addressBook = [ABAddressBook sharedAddressBook];
NSArray *contacts = [addressBook people];
rawContacts=contacts;
NSArray *firstNames = [rawContacts valueForKey:#"First"];
NSArray *lastNames = [rawContacts valueForKey:#"Last"];
NSArray *organization = [rawContacts valueForKey:#"Organization"];
NSMutableArray *fullNames = [NSMutableArray array];
for(int i = 0; i < [firstNames count]; i++)
{
NSString *fullName = [NSString stringWithFormat:#"%# %# %#",
[firstNames objectAtIndex:i],
[lastNames objectAtIndex:i],
[organization objectAtIndex:i]];
[fullNames addObject:fullName];
}
NSMutableArray *fullList = [[NSMutableArray alloc]initWithArray:fullNames];
[fullList removeObjectIdenticalTo: #"<null>"];
sortedContacts = [fullList sortedArrayUsingSelector:#selector(compare:)];
NSLog(#"%#",sortedContacts);
}
I've tried so many things that I just can't see the forest for the trees anymore.
The text <null> is how the singleton instance of NSNull describes itself. That is, it's what -[NSNull description] returns.
In turn, these NSNull objects are getting into your firstNames, lastNames, and organization arrays because that's what Key-Value Coding does when you call -valueForKey: on an array and some of the elements return nil when that message is forwarded on to them with the same key. That is, calling [rawContacts valueForKey:#"First"] causes NSArray to call [element valueForKey:#"First"] for each element in rawContacts and to put the result in the array it builds. But, since an array can't contain nil, if one of those elements returns nil from [element valueForKey:#"First"], an NSNull object is added in its place.
Then, you are formatting the string fullName from the corresponding elements of firstNames, lastNames, and organization. You need to check if any of those elements are NSNull using if ([value isKindOfClass:[NSNull class]]) and handling that. For instance, you might just skip that record. Or you might combine the available fields and leave out any unavailable ones.
In any case, none of the elements of fullList will be #"<null>" because formatting values into #"%# %# %#" can never result in that string. (It might be #"<null> <null> <null>" or something like that, but never just #"<null>".)
A quick look at your code suggests you cannot get any empty strings added to your array, (a) you add elements using:
[fullNames addObject:fullName];
and fullName is created using:
[NSString stringWithFormat:#"%# %# %#" ...
so even if the %#'s get replaced by nothing you'll still have 2 spaces...
Maybe this is why all the things you've tried fail, if you're looking for empty strings you won't find them.
(Addendum: Question now says you're looking for #"<null>", you won't get that either for the same reason - there is at least two spaces in your string.)
The simple answer to removing invalid entries in fullNames is not to add them in the first place. You are adding elements in a loop (for), and conditional logic (e.g. if) inside the loop to determine whether you have something valid to add - however you define "something valid" - and only add an item to fullNames if so.
HTH
I'm not really familiar with the AddressBook framework, however this might be what's causing the confusion:
The values you collect in your arrays firstNames, lastNames and organization can be of type NSString or NSNull. You have to do any null-checking within the for-loop, before the fullName-string is constructed.
Remove this useless line:
[fullList removeObjectIdenticalTo: #"<null>"];
And replace the contents of your for-loop with the following code:
for(int i = 0; i < [firstNames count]; i++)
{
NSString *firstName = [firstNames objectAtIndex:i];
NSString *lastName = [lastNames objectAtIndex:i];
NSString *org = [organization objectAtIndex:i];
NSMutableArray *namesArray = [NSMutableArray array];
if ([firstName isKindOfClass:[NSString class]])
[namesArray addObject:firstName];
if ([lastName isKindOfClass:[NSString class]])
[namesArray addObject:lastName];
if ([org isKindOfClass:[NSString class]])
[namesArray addObject:org];
if (namesArray.count > 0)
[fullNames addObject:[namesArray componentsJoinedByString:#" "]];
}
I have a fun challenging problem. So I have a mutable array that contains all of my items. I have a textfield that **might have one or two of these items if the person types them in. **
items= [[NSArray alloc]initWithObjects:#"apple", #"orange", #"pear", nil];
items2= [[NSArray alloc]initWithObjects:#"cheese", #"milk", #"eggs", nil];
Allitems= [NSMutableArray array];
[Allitems addObjectsFromArray:items];
[Allitems addObjectsFromArray:items2];
NSArray*WORDS =[Textfield componentsSeparatedByString:#" "];
I am trying to detect what specific words from **Allitems are in the textfield. (If the textfield contains any string from ALLitems, how can I find what specific string?**
for (int i = 0; i < [Allitems count]; i++)
{
NSString *grabstring;
grabstring=[Allitems objectAtIndex:i];
if (textfield isEqualto:grabstring){
?????
pull that specific string from allitems.
}
}
You want the intersection of two sets:
NSMutableSet* intersectionSet = [NSMutableSet setWithArray:Allitems];
[intersectionSet intersectSet:[NSSet setWithArray:WORDS]];
NSArray* intersectionArray = [intersectionSet allObjects];
After this intersectionArray contains the items that are present in both Allitems and WORDS.
BTW, why do you capitalise variable names in a non-standard and inconsistent manner? Why not just allItems and words?
As #Arkku suggests: It's better to switch the arrays. In your example it does not matter much, but in case Allitems were (very) big, you can save (a lot of) memory and CPU usage:
NSMutableSet* intersectionSet = [NSMutableSet setWithArray:WORDS];
[intersectionSet intersectSet:[NSSet setWithArray:Allitems]];
NSArray* intersectionArray = [intersectionSet allObjects];
There are a various ways of doing it, each with different pros and cons. Let's have the following (consistently capitalized) variables in common for each case:
NSArray *allItems = #[ #"apple", #"orange", #"pear", #"cheese", #"milk", #"egg" ];
NSString *textFieldText = #"CHEESE ham pear";
NSArray *words = [textFieldText.lowercaseString componentsSeparatedByString:#" "];
NSPredicate
NSArray *matchingItems = [allItems filteredArrayUsingPredicate:
[NSPredicate predicateWithFormat:#"SELF IN %#", words]];
This is perhaps the shortest (in lines of code) way, but not the most performant if allItems can be very long as it requires traversing all of it.
Iteration
Of course you could also simply iterate over the collection and do the matching manually:
NSMutableArray *matchingItems = [NSMutableArray array];
for (NSString *item in allItems) {
if ([words containsObject:item]) {
[matchingItems addObject:item];
}
}
Again requires traversing all of allItems (although you could break the iteration if all words are matched).
In addition to the for loop there are of course many other ways for iteration, e.g., enumerateObjectsUsingBlock:, but they are unlikely to have any advantage here.
NSSet
NSSet is often a good option for this kind of matching since testing set membership is faster than with NSArray. However, if using the most straightforward method intersetSet: (in NSMutableSet) care must be taken to not inadvertently create a large mutable set only to discard most of its items.
If the order of allItems does not matter, the best way would be to change it from an array into a set and always keep that set around, i.e., instead of creating the array allItems, you would create an NSSet:
NSSet *setOfAllItems = [NSSet setWithArray:allItems];
Or if it needs to be mutable:
NSMutableSet *setOfAllItems = [NSMutableSet set];
[setOfAllItems addObjectsFromArray:items1];
[setOfAllItems addObjectsFromArray:items2];
Then, when you have that set, you create a temporary mutable set out of words (which is presumably always the smaller set):
NSMutableSet *setOfMatches = [NSMutableSet setWithArray:words];
[setOfMatches intersectSet:setOfAllItems];
NSArray *matchingItems = setOfMatches.allObjects;
This would be likely be the most performant solution if setOfAllItems is large, but note that the matches will then need to be exact. The other methods are more easily adapted to things like matching the strings in words against fields of objects or keys in a dictionary (and returning the matched objects rather than the strings). In such a case one possibility to consider would be an NSDictionary mapping the words to match to the objects to return (also fast to then iterate over words and test for membership in the dictionary).
Conversion to string
And, since the question included conversion of matches to a string:
[matchingItems componentsJoinedByString:#", "]
In the example case this would result in the string "pear, cheese" (or possibly "cheese, pear" if using sets).
I've got the following NSArray :
NSArray myArray = #[#{#300:#"5 min"},
#{#900:#"15 min"},
#{#1800:#"30 min"},
#{#3600:#"1 hour"}];
I want the list of value of my dictionaries :
#[#"5 min",#"15 min",#"30 min",#"1 hour"]
And the list of key of my dictionaries :
#[#300, #900, #1800, #3600]
What is the best way to do that ? I was thinking about predicate, but I don't know how to use it ?
Without some code to show how you'd want to go about this it is difficult to be sure exactly what you are after, and there is a bit of confusion in the question.
First, a predicate is exactly that - a statement that can be proven true or false. Predicates are hence used in logic expressions, including those employed implicitly in database queries - such as Core Data.
That is not what you want, if I read your question correctly. What you want is to reduce the complexity of your data model, removing some excess (one would hope) information in the process. A sort of flattening of an array of dictionaries.
Fair enough.
I can also see how the confusion with predicates came about - they are most often constructed using Key-Value Coding. KVC, as it is also known, is a very powerful technique that can accomplish what you are after. It just does not have much to do with a logic statement.
Having cleared that up, with KVC you can do what you want, and with minimal fuss. It goes like this:
NSArray *values = [myArray valueForKeyPath: #"#unionOfArrays.#allValues"];
NSArray *keys = [myArray valueForKeyPath: #"#unionOfArrays.#allKeys"];
A brief explanation might be in order:
The results that we want are
All the values (or keys) of each dictionary, obtaining an array of arrays of values (or keys)
Then we want to flatten these arrays into a single array.
To obtain all values (or keys) from a dictionary using KVC, the special key is #allValues or #allKeys, respectively.
The #unionOfArrays operator makes a union of the arrays obtained from the expression that follows it, i.e., flattens it into the array you wanted.
The price you pay for this coding simplicity is that you have to use KVC key paths with collection operators, which are just strings in your code. You therefore lose any help from the compiler with syntax and it doesn't check that the keys you enter exist in the objects. Similarly, the debugger and error messages are unhelpful if you mistype or use the wrong operator, for instance.
You can use dictionary property allValues to get all values of dictionary.
Try this code in your case
NSArray *myArray = #[#{#300:#"5 min"},
#{#900:#"15 min"},
#{#1800:#"30 min"},
#{#3600:#"1 hour"}];
NSMutableArray *arr = [NSMutableArray array];
for (NSDictionary *dict in myArray) {
[arr addObject:[[dict allValues] objectAtIndex:0]];
}
NSLog(#"%#",arr);
Note : Make sure you have only one value in each dictionary.
it will return
[
5 min,
15 min,
30 min,
1 hour
]
#johnyu's answers is technically correct, but I don't see any reason to include the secondary loop, especially if the data structure will remain the same.
NSArray *myArray = #[#{#300:#"5 min"},
#{#900:#"15 min"},
#{#1800:#"30 min"},
#{#3600:#"1 hour"}];
NSMutableArray *arrayOfValues = [NSMutableArray new];
NSMutableArray *arrayOfKeys = [NSMutableArray new];
for (NSDictionary *dictionary in myArray) {
[arrayOfValues addObject:dictionary.allValues[0]];
[arrayOfKeys addObject:dictionary.allKeys[0]];
}
NSLog(#"%#",arrayOfKeys);
NSLog(#"%#",arrayOfValues);
Try this:
NSArray *myArray = #[#{#300:#"5 min"},
#{#900:#"15 min"},
#{#1800:#"30 min"},
#{#3600:#"1 hour"}];
NSMutableArray *keyArray = [[NSMutableArray alloc] init];
NSMutableArray *valueArray = [[NSMutableArray alloc] init];
for (NSDictionary *dictionary in myArray) {
for (NSString *key in dictionary) {
[keyArray addObject:key];
[valueArray addObject:[dictionary objectForKey:key]];
}
}
I get an array from a JSON and I parse it into an NSMutableArray (this part is correct and working). I now want to take that array and print the first object to a Label. Here is my code:
NSDictionary *title = [[dictionary objectForKey:#"title"] objectAtIndex:2];
arrayLabel = [title objectForKey:#"label"];
NSLog(#"arrayLabel = %#", arrayLabel); // Returns correct
//Here is where I need help
string = [arrayLabel objectAtIndex:1]; //I do not get the first label (App crashes)
NSLog(#"string = %#", string);
other things that I have already tried are as follows:
string = [NSString stringWithFormat:#"%#", [arrayImage objectAtIndex:1]];
and
string = [[NSString alloc] initWithFormat:#"%#", [arrayImage objectAtIndex:1]];
Any help is greatly appriciated!
EDIT: The app does not return a single value and crashes.
Your code doesn't match the structure of your JSON. In your comment on the deleted answer, you said you got an exception when sending objectAtIndex: to an NSString. In your case, arrayLabel isn't an array when you think it is.
If your JSON has an object, your code needs to treat it as an NSDictionary. Likewise for arrays and NSArray and strings and NSString.
In addition to whatever else was going on, you repeatedly refer to "first" but use the index 1. In most C-based programming languages (and others, as well) the convention is that indexes into arrays are 0-based. So, use index 0 to get the first element.
I want to create instance variables dynamically at runtime, and I want to add these variables to a category. The number of the instance variables may change based on the configuration/properties file which I am using for defining them.
Any ideas??
Use Associative References - this is tricky, but that is the mechanism invented specifically for your use case.
Here is an example from the link above: first, you define a reference and add it to your object using objc_setAssociatedObject; then you can retrieve the value back by calling objc_getAssociatedObject.
static char overviewKey;
NSArray *array = [[NSArray alloc] initWithObjects:# "One", #"Two", #"Three", nil];
NSString *overview = [[NSString alloc] initWithFormat:#"%#", #"First three numbers"];
objc_setAssociatedObject (
array,
&overviewKey,
overview,
OBJC_ASSOCIATION_RETAIN
);
[overview release];
NSString *associatedObject = (NSString *) objc_getAssociatedObject (array, &overviewKey);
NSLog(#"associatedObject: %#", associatedObject);
objc_setAssociatedObject (
array,
&overviewKey,
nil,
OBJC_ASSOCIATION_ASSIGN
);
[array release];
I'd be inclined to just use a NSMutableDictionary (see NSMutableDictionary Class Reference). Thus, you would have an ivar:
NSMutableDictionary *dictionary;
You'd then initialize it:
dictionary = [NSMutableDictionary dictionary];
You can then save values to it dynamically in code, e.g.:
dictionary[#"name"] = #"Rob";
dictionary[#"age"] = #29;
// etc.
Or, if you are reading from a file and don't know what the names of the keys are going to be, you can do this programmatically, e.g.:
NSString *key = ... // your app will read the name of the field from the text file
id value = ... // your app will read the value of the field from the text file
dictionary[key] = value; // this saves that value for that key in the dictionary
And if you're using an older version of Xcode (before 4.5), the syntax is:
[dictionary setObject:value forKey:key];
Depends on exactly what you want to do, the question is vague but if you want to have several objects or several integers or so on, arrays are the way to go. Say you have a plist with a list of 100 numbers. You can do something sort of like this:
NSArray * array = [NSArray arrayWithContentsOfFile:filePath];
// filePath is the path to the plist file with all of the numbers stored in it as an array
That will give you an array of NSNumbers, you can then turn that into an array of just ints if you want like this;
int intArray [[array count]];
for (int i = 0; i < [array count]; i++) {
intArray[i] = [((NSNumber *)[array objectAtIndex:i]) intValue];
}
Whenever you want to get an integer from a certain position, lets say you want to look at the 5th integer, you would do this:
int myNewInt = intArray[4];
// intArray[0] is the first position so [4] would be the fifth
Just look into using a plist for pulling data, it will them be really easy to create arrays of custom objects or variables in your code by parsing the plist.