Can someone please show me the code for sorting an NSMutableArray? I have the following NSMutableArray:
NSMutableArray *arr = [[NSMutableArray alloc] init];
with elements such as "2", "4", "5", "1", "9", etc which are all NSString.
I'd like to sort the list in descending order so that the largest valued integer is highest in the list (index 0).
I tried the following:
[arr sortUsingSelector:#selector(compare:)];
but it did not seem to sort my values properly.
Can someone show me code for properly doing what I am trying to accomplish? Thanks!
You should use this method:
[arr sortedArrayUsingSelector:#selector(caseInsensitiveCompare:)];
in a NSArray or:
[arr sortUsingSelector:#selector(caseInsensitiveCompare:)];
in a "inplace" sorting NSMutableArray
The comparator should return one of this values:
NSOrderedAscending
NSOrderedDescending
NSOrderedSame
It's pretty simple to write your own comparison method for strings:
#implementation NSString(compare)
-(NSComparisonResult)compareNumberStrings:(NSString *)str {
NSNumber * me = [NSNumber numberWithInt:[self intValue]];
NSNumber * you = [NSNumber numberWithInt:[str intValue]];
return [you compare:me];
}
#end
If the array's elements are just NSStrings with digits and no letters (i.e. "8", "25", "3", etc.), here's a clean and short way that actually works:
NSArray *sortedArray = [unorderedArray sortedArrayUsingComparator:^(id a, id b) {
return [a compare:b options:NSNumericSearch];
}];
Done! No need to write a whole method that returns NSComparisonResult, or eight lines of NSSortDescriptor...
IMHO, easiest way to sort such array is
[arr sortedArrayUsingDescriptors:#[[NSSortDescriptor sortDescriptorWithKey:#"self.intValue" ascending:YES]]]
If your array contains float values, just change key to self.floatValue or self.doubleValue
The easiest way would be to make a comparator method like this one
NSArray *sortedStrings = [stringsArray sortedArrayUsingComparator:^NSComparisonResult(NSString *firstString, NSString *secondString) {
return [[firstString lowercaseString] compare:[secondString lowercaseString]];
}];
Related
There is an array in my app having multiple same values in it. I need to delete only one value at a time from array whether it has same more values in it.
Level1 Business,
Level2 Economy,
Level2 Economy,
Level1 Business
How this can be achieved, and main thing is that these values are dynamic these can be more or less also. Please guide for above.
Below is what i tried.
if([arr containsObject:[NSString stringWithFormat:#"%d",ind]]){
[arr removeObject:[NSString stringWithFormat:#"%d",ind]];
}
This thing removes all similar entries, not required. Thanks in advance.
try like this,
NSArray *array = [NSArray arrayWithObjects:#"Level1 Business", #"Level2 Economy", #"Level2 Economy", #"Level1 Business", nil];
NSMutableArray *mainarray=[[NSMutableArray alloc]initWithArray:array];
int n=[mainarray indexOfObject:#"Level2 Economy"];//it gives first occurence of the object in that array
if(n<[mainarray count]) // if the object not exist then it gives garbage value that's why here we have to take some condition
[mainarray removeObjectAtIndex:n];
NSLog(#"%#",mainarray);
O/P:-
(
"Level1 Business",
"Level2 Economy",
"Level1 Business"
)
As you say,
[array removeObject:#"SomeObject"];
removes all instances of where isEqual: returns YES. To remove only the first instance, you can use something like
NSUInteger index = [array indexOfObject:#"SomeObject"];
if(index != NSNotFound) {
[array removeObjectAtIndex:index];
}
Use [arr removeObjectAtIndex:yourIndex ] to remove your object at perticular postion at dynamic
Sample Code :
NSMutableArray *arr = [[NSMutableArray alloc]initWithObjects:#"hello",#"hi",#"hi",#"hi",#"hi",#"hi",#"hi",#"hi",#"hi",#"hi",#"hi",#"hi",#"hi",nil];
NSUInteger obj = [arr indexOfObject:#"hi"]; //Returns the lowest integer of the specified object
[arr removeObjectAtIndex:obj]; //removes the object from the array
NSLog(#"%#",arr);
In your Case :
if([arr containsObject:[NSString stringWithFormat:#"%d",ind]])
{
NSUInteger obj = [arr indexOfObject:[NSString stringWithFormat:#"%d",ind]]; //Returns the lowest integer of the specified object
[arr removeObjectAtIndex:obj];
}
Here your requirement is like definition of NSSet, which contains unique objects only.
But this will implies only if both the same value objects, are really in referring to same memory location as well.
If this is the case then and then, you can try code mentioned below:
// create set from an array
NSSet *telephoneSet = [NSSet setWithArray: myArray];
// create array from a set
NSMutableArray *array = [NSMutableArray arrayWithArray:[set allObjects]];
I don't know whether it will work for your requirement or not. But for that, it would be required to check the object equality level.
Still it might help you as an less line of code.
NSMutableArray *uniques= [[NSMutableArray alloc] init];
for (NSString *word in duplicateWordsArray){
if (!uniques.contains(word)){
[ uniques addObject:word];
}
}
I wrote this from my phone so it isn't formatted for code, but this will do it for you quickly and you'll have an array (uniquearray) that has unique words. Then you can use that one or set your original array = to unique array
NSArray *input = [NSArray arrayWithObjects:#"Level1 Business", #"Level2 Economy", #"Level2 Economy", #"Level1 Business", nil];
NSMutableArray *output = [[NSMutableArray alloc] init];
[output addObject:[input objectAtIndex:0]];
for(NSString *value in input) {
if(![output containsObject:value])
[output addObject:value];
}
The title pretty much says it all, but just to clarify: I have an NSMutableDictonary containing several NSMutableArrays. What I would like to do is find any value that is present in multiple arrays (there will not be any duplicates in a single array) and return that value. Can someone please help? Thanks in advance!
Edit: For clarity's sake I will specify some of my variables:
linesMutableDictionary contains a list of Line objects (which are a custom NSObject subclass of mine)
pointsArray is an array inside each Line object and contains the values I am trying to search through.
Basically I am trying to find out which lines share common points (the purpose of my app is geometry based)
- (NSValue*)checkForDupes:(NSMutableDictionary*)dict {
NSMutableArray *derp = [NSMutableArray array];
for (NSString *key in [dict allKeys]) {
Line *temp = (Line*)[dict objectForKey:key];
for (NSValue *val in [temp pointsArray]) {
if ([derp containsObject:val])
return val;
}
[derp addObjectsFromArray:[temp pointsArray]];
}
return nil;
}
this should work
If by duplicates you mean returning YES to isEqual: you could first make an NSSet of all the elements (NSSet cannot, by definition, have duplicates):
NSMutableSet* allElements = [[NSMutableSet alloc] init];
for (NSArray* array in [dictionary allValues]) {
[allElements addObjectsFromArray:array];
}
Now you loop through the elements and check if they are in multiple arrays
NSMutableSet* allDuplicateElements = [[NSMutableSet alloc] init];
for (NSObject* element in allElements) {
NSUInteger count = 0;
for (NSArray* array in [dictionary allValues]) {
if ([array containsObject:element]) count++;
if (count > 1) {
[allDuplicateElements addObject:element];
break;
}
}
}
Then you have your duplicate elements and don't forget to release allElements and allDuplicateElements.
If I have an NSArray of custom objects (in this case Core Data objects), how would I put all the items of a particular attribute in another NSArray. Is there a way I can use blocks?
For instance, if the class is People, and one of the attributes is age, and there are five objects in the array of people, then the final NSArray would just show the ages:
{ 12, 45, 23, 43, 32 }
Order is not important.
EDIT I have added a blocks based implementation too alongwith the selector based implementation.
What you are looking for is something equivalent to the "map" function from the functional world (something which, unfortunately, is not supported by Cocoa out of the box):
#interface NSArray (FunctionalUtils)
- (NSArray *)mapWithSelector:(SEL)selector;
- (NSArray *)mapWithBlock:(id (^)(id obj))block;
#end
And the implementation:
#implementation NSArray (FunctionalUtils)
- (NSArray *)mapWithSelector:(SEL)selector {
NSMutableArray *result = [[NSMutableArray alloc] initWithCapacity:[self count]];
for (id object in self) {
[result addObject:[object performSelector:selector]];
}
return [result autorelease];
}
- (NSArray *)mapWithBlock:(id (^)(id obj))block {
NSMutableArray *result = [[NSMutableArray alloc] initWithCapacity:[self count]];
for (id object in self) {
[result addObject:block(object)];
}
return [result autorelease];
}
#end
Now, when you need to "map" from people to their ages, you can just do this:
ages = [people mapWithSelector:#selector(age)];
OR
ages = [people mapWithBlock:^(Person *p) { return [p age]; }];
The result, ages, will be a new NSArray containing just the ages of the people. In general, this will work for any sort of simple mapping operations that you might need.
One caveat: Since it returns an NSArray, the elements inside ages should be NSNumber, not a plain old integer. So for this to work, your -age selector should return an NSNumber, not an int or NSInteger.
Assuming that each object has a method called "age" that returns an NSNumber *, you should be able to do something like the following:
-(NSArray *)createAgeArray:(NSArray *)peopleArray {
NSMutableArray *result = [[NSMutableArray alloc] initWithCapacity:[peopleArray count]];
[peopleArray enumerateObjectsUsingBlock:^(id person, NSUInteger i, BOOL *stop) {
[result addObject:[person age]];
}];
return [result autorelease];
}
Okeh. Here is the deal:
Have have a NSMutualDictionary with words as keys (say names). The value objects is a NSNumber (like rating)
NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] init];
[dictionary setObject:[NSNumber intValue:1] forKey:#"Melvin"];
[dictionary setObject:[NSNumber intValue:2] forKey:#"John"];
[dictionary setObject:[NSNumber intValue:3] forKey:#"Esben"];
I want to sort them with the highest ratings first.
I know I'm going to do it like this:
[searchWords keysSortedByValueUsingSelector:#selector(intCompare:)];
But not sure how to implement intCompare. (the compare method)
Can anybody point me in the right direction?
- (NSComparisonResult) intCompare:(NSString *) other
{
//What to do here?
}
I want to get an NSArray with {Esben, John, Melvin}.
Since the objects you put into the dictionary are NSNumber instances you should change the method signature a bit. But the full implementation is really easy:
-(NSComparisonResult)intCompare:(NSNumber*)otherNumber {
return [self compare:otherNumber];
}
In fact I see no reason as to why you need to do your own intCompare: method, when you could go with the compare: that NSNumber already has.
These constants are used to indicate how items in a request are ordered.
enum {
NSOrderedAscending = -1,
NSOrderedSame,
NSOrderedDescending
};
typedef NSInteger NSComparisonResult;
That is taken from Apple's dev documentataion on Data types... now all you have to do is check which one is bigger. All of this is done for you though. Simply pass in #selector(compare:) and that should do it. As your values are NSNumbers and NSNumber implements the compare: function. Which is what you want :)
NSArray *sortedArray = [searchWords sortedArrayUsingSelector:#selector(compare:) ];
or you might well as used, here is the implementation of your intCompare selector
- (NSComparisonResult) intCompare:(NSString *) other
{
int myValue = [self intValue];
int otherValue = [other intValue];
if (myValue == otherValue) return NSOrderedSame;
return (myValue < otherValue ? NSOrderedAscending : NSOrderedDescending);
}
I have a NSMutableArray which contains a few NSString objects. How can I test if the array contains a particular string literal?
I tried [array containsObject:#"teststring"] but that doesn't work.
What you're doing should work fine. For example
NSArray *a = [NSArray arrayWithObjects:#"Foo", #"Bar", #"Baz", nil];
NSLog(#"At index %i", [a indexOfObject:#"Bar"]);
Correctly logs "At index 1" for me. Two possible foibles:
indexOfObject sends isEqual messages to do the comparison - you've not replaced this method in a category?
Make sure you're testing against NSNotFound for failure to locate, and not (say) 0.
[array indexOfObject:object] != NSNotFound
Comparing against string literals only works in code examples. In the real world you often need to compare against NSString* instances in e.g. an array, in which case containsObject fails because it compares against the object, not the value.
You could add a category to your implementation which extends NS(Mutable)Array with a method to check wether it contains the string (or whatever other type you need to compare against);
#implementation NSMutableArray (ContainsString)
-(BOOL) containsString:(NSString*)string
{
for (NSString* str in self) {
if ([str isEqualToString:string])
return YES;
}
return NO;
}
#end
You may also use a predicate:
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"SELF IN %#", theArray];
BOOL result = [predicate evaluateWithObject:theString];
for every object
[(NSString *) [array objectAtIndex:i] isEqualToString:#"teststring"];