Can someone help take a look at this method and advise please.. SOmethings seems not quite right.
for(int i = 0; i<sizeof(_annotation2) - 5 ; i++){
[a.annotationsPatients addObject:[_annotation2 objectAtIndex:i]];
}
You cannot use sizeof() to get the number of elements in an NSArray. You use count.
for(int i = 0; i<[_annotation2 count] - 5 ; i++){
[a.annotationsPatients addObject:[_annotation2 objectAtIndex:i]];
}
You're using sizeof incorrectly. sizeof gets the size of a given data type, not the length of what I assume is an NSArray. To get the length of an NSArray, use the count method, like so:
NSUInteger arrayLength = [someArray count];
for (int x = 0; x < arrayLength; ++x)
{
// do whatever in here
}
Actually "count" method is used instead of "sizeof".
Review your code as below:
for(int i = 0; i<[_annotation2 count] - 5 ; i++){
[a.annotationsPatients addObject:[_annotation2 objectAtIndex:i]];
}
Related
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Generating non-repeating random numbers
Here is my code
NSUInteger count = 10;
for (NSUInteger i = 0; i < count; ++i) {
NSLog(#"%d",NeedRandomNumberWithoutRepeat);
}
this output should be like
8
7
9
2
1
4
6
3
5
0
Which is random and not repeating numbers
This should work:
NSUInteger count = 10;
NSMutableArray *array = [[NSMutableArray alloc]init];
for (NSUInteger i = 0; i < count; ++i) {
[array addObject:[NSNumber numberWithInt:i]];
}
NSMutableArray *copy = [array mutableCopy];
array = [[NSMutableArray alloc]init];
while ([copy count] > 0)
{
int index = arc4random() % [copy count];
id objectToMove = [copy objectAtIndex:index];
[array addObject:objectToMove];
[copy removeObjectAtIndex:index];
}
This answer is modified version from one of my answer in SO.
So, you may find something strange here, you can however use this as your requirement is similar.
int TOTAL_NUMBER=10;
NSMutableArray *alreadyGeneratedNumbers;
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification{
alreadyGeneratedNumbers=[NSMutableArray new];
}
-(int)generateRandomNumber{
int low_bound = 0;
int high_bound = TOTAL_NUMBER;
int width = high_bound - low_bound;
int randomNumber = low_bound + arc4random() % width;
return randomNumber;
}
- (IBAction)button:(id)sender {
NSMutableArray *shuffle = [[NSMutableArray alloc] initWithCapacity:1];
BOOL contains=YES;
while ([shuffle count]<1) {
NSNumber *generatedNumber=[NSNumber numberWithInt:[self generateRandomNumber]];
if (![alreadyGeneratedNumbers containsObject:generatedNumber]) {
[shuffle addObject:generatedNumber];
contains=NO;
[alreadyGeneratedNumbers addObject:generatedNumber];
}
}
NSLog(#"shuffle %#",shuffle);
NSLog(#"Next Batch");
if ([alreadyGeneratedNumbers count] >= TOTAL_NUMBER) {
NSLog(#"\nGame over, Want to play once again?");//or similar kind of thing.
[alreadyGeneratedNumbers removeAllObjects];
}
}
You put the available numbers in an array, and take the index calculated with arc4random() that goes from 0 to the size of the array -1.When a number comes out you take it away from the array:
NSMutableArray* availableNumbers=[NSMutableArray new];
for(NSUInteger i=0; i<10; i++)
{
[availableNumbers addObject: #(i)];
}
for(NSUInteger i=0; i<10; i++)
{
NSUInteger index= arc4random()%availableNumbers.count;
NSNumber* number= availableNumbers[index];
NSLog(#"%#",number);
[availableNumbers removeObjectAtIndex: index];
}
PS: At the last iteration is useless to sue arc4random(), since there's only one number inside.
I'm trying to shuffle an NSMutableArray so that its order will be mixed up every-time someone loads the view.
In my -(void)viewDidLoad I'm putting the following code (as suggested by other users):
NSMutableArray *shuffleTwo = [self.chosenTeamDict objectForKey:#"clubs"];
int random = arc4random() % [shuffleTwo count];
for (int i = 0; i < [shuffleTwo count]; i++) {
[shuffleTwo exchangeObjectAtIndex:random withObjectAtIndex:i];
}
NSLog(#"%#", shuffleTwo);
But when I do this and try and run the page, I get the following error:
2012-07-09 18:42:16.126 Kit-Quiz[6505:907] (null)
libc++abi.dylib: terminate called throwing an exception
Can anyone advice either a new way of shuffling this array, or advice me on how to avoid this error..!? I'm building for iOS 5 and I'm using Xcode45-DP1. Thanks in advance!
(EDIT)
I've also tried this method and I get the same error:
NSMutableArray *shuffledArray = [[NSMutableArray alloc] init];
NSMutableArray *standardArray = [self.chosenTeamDict objectForKey:#"clubs"];
for(int s = 0; s < [standardArray count]; s++){
int random = arc4random() % s;
[shuffledArray addObject:[standardArray objectAtIndex:random]];
}
NSLog(#"%#", shuffledArray);
NSMutableArray *standardArray = [self.chosenTeamDict objectForKey:#"clubs"];
int length = 10; // int length = [yourArray count];
NSMutableArray *indexes = [[NSMutableArray alloc] initWithCapacity:length];
for (int i=0; i<10; i++) [indexes addObject:[shuffledArray objectAtIndex:i]];
NSMutableArray *shuffle = [[NSMutableArray alloc] initWithCapacity:length];
while ([indexes count])
{
int index = rand()%[indexes count];
[shuffle addObject:[indexes objectAtIndex:index]];
[indexes removeObjectAtIndex:index];
}
for (int i=0; i<[shuffle count]; i++) NSLog(#"%#", [shuffle objectAtIndex:i]);
NSLog(#"%#", shuffle);
^^ ANSWER
Try Fisher-Yates shuffle. It goes like this:
int count = shuffledArray.count;
for(int i=count; i>0; i--) {
int j = arc4random_uniform(count);
[shuffledArray exchangeObjectAtIndex:j withObjectAtIndex:i];
}
make sure that your array is non-nil and all the entries are allocated objects :)
Source: Fisher-Yates Shuffle
First, you really should enable exception breakpoints. In XCode on the left-hand panel, click the breakpoint tab, click the "+" sign at the bottom-left -> exception breakpoint -> done.
I suspect your problem lies here:
int random = arc4random() % [shuffleTwo count];
If [shuffleTwo count] evaluates to zero (also if shuffleTwo is nil) it will throw a division by zero exception. Edit: Doesn't seem to be the case in Objective-C.
I have an NSMutableArray populated with NSIntegers. I need to loop through the array. I could do:
// given NSMutableArray *array of NSIntegers
NSUInteger n = [array count];
for (NSInteger i = 0; i < n; i++) {
NSInteger x = [array objectAtIndex:i];
// query SQLite WHERE id = x
}
However, it seems that a for (object in array) loop would be cleaner. iOS 5 does not accept NSIntegers or NSNumbers as objects in for-in loops. Should I loop through the array with NSObjects, casting the NSObject to an NSInteger during each iteration? Is there another way? Or is a for loop like the one above the cleanest solution to this problem?
In Objective-C you can use a for-in loop with NSNumber like this:
NSArray *array = /*NSArray with NSNumber*/;
for (NSNumber *n in array) {
NSLog(#"i: %d", [n intValue]);
}
Check this out.
Mostly, you will not be allowed to have an NSMutableArray of NSUInteger (aka unsigned long) as it's not an objective-c object.
You may use the c style.
NSUInteger array[] = {value1,value2,value3};
int size = sizeof(array)/sizeof(array[0]);
for (int i=0; i<size; i++) {
NSInteger value = array[i];
// do whatever you want
}
I have an array of Place objects. Each Place object has a name and code property, both strings. Each Place object already has a code, but I need to look up the name property from a server. I get back 2 arrays: one contains name, the other codes. These arrays are ordered so that the name at some index in the nameArray corresponds exactly with the code at the same index of the codeArray.
I have been looping through the array of Place objects, then checking to see if the code property for that Place is the same as the current index in the codeArray. If it is, I set the name of that Place by using the same index in the nameArray:
for(int i = 0; i < [placesArray count]; i++)
{
for(int j = 0; j < [codeArray count]; j++) {
if([[[placesArray objectAtIndex:i] code] isEqualToString:[codeArray objectAtIndex:j]]) {
[[placesArray objectAtIndex:i] setName:[nameArray objectAtIndex:j]];
}
}
}
This works but isn't terribly fast - it can take 30 seconds with 1000+ Places to loop through.
Is there a faster way?
As with anytime you're trying to optimize performance, you should profile the code using Instruments to find out where the bottleneck actually is. That said, looping through the placesArray for each name in the nameArray and doing a string comparison is pretty inefficient.
How about something like this?
NSMutableDictionary *placesByCode = [NSMutableDictionary dictionaryWithCapacity:[placesArray count]];
for (Place *aPlace in placesArray) {
[dictionary setObject:aPlace forKey:aPlace.code];
}
NSMutableDictionary *namesByCode = [NSMutableDictionary dictionaryWithCapacity:[namesArray count]];
for (int i=0; i<[namesArray count]; i++) {
NSString *name = [namesArray objectAtIndex:i];
NSString *code = [codeArray objectAtIndex:i];
[namesByCode setObject:name forKey:code];
}
for (NSString *code in namesByCode) {
Place *place = [placesByCode objectForKey:code];
place.name = [namesByCode objectForKey:namesByCode];
}
Looking up each place by its code in the dictionary should be quite a bit faster than manually looping through the whole place array for each name.
You can use for NSArray -containsObject
if ([myarray containsObject:myObject]) {
// ...
}
Try using a break statement in the inner loop. This way you don't need to loop through the entire loop each time.
for(int i = 0; i < [placesArray count]; i++)
{
for(int j = 0; j < [codeArray count]; j++) {
if([[[placesArray objectAtIndex:i] code] isEqualToString:[codeArray objectAtIndex:j]]) {
[[placesArray objectAtIndex:i] setName:[nameArray objectAtIndex:j]];
break;
}
}
}
You could also make the second array become smaller as you find more results. It will cost you more memory but 1000 strings isn't much anyway.
NSMutableArray * tempCodeArray = [NSMutableArray arrayWithArray:codeArray];
for(int i = 0; i < [placesArray count]; i++)
{
for(int j = 0; j < [tempCodeArray count]; j++) {
if([[[placesArray objectAtIndex:i] code] isEqualToString:[tempCodeArray objectAtIndex:j]]) {
[[placesArray objectAtIndex:i] setName:[nameArray objectAtIndex:j]];
[tempCodeArray removeObjectAtIndex:j];
break;
}
}
}
The problem was not the counting for the array, it's the embedded for loop which will take O(n*n) and in Andrew's solution, it's only O(n)+O(n)+O(n)+whatever take to find a object of the key in the dictionary, which i guess would be in a hash table lookup and that's really fast.
Colby, you probably will be ok with Andrew's solution. If you still wanna improve the performance, then a good idea would be sort the array's first then do lookup.
Hope this helps.
Here I am having a situation, I'm using the following code:
int x=0;
for (int i=0; i<=[arrayDeals count]-1; i++) {
x++;
//NSString *deal = [arrayDeals objectAtIndex:i];
combinedArr = [[NSMutableArray alloc]initWithObjects:
[CustomObject customObjectWithName:[arrayDeals objectAtIndex:i] andNumber:x],nil];
}
I need to load the values from arrayDeals and the 'x' value into combinedArr. So, I put this in a for loop. But i got only one value from each arrays. What is went wrong here? Please help me. (here CustomObject is a NSObject)
Thank you.
Well there are many things wrong with the code you posted, but I think this is what you want:
int x = 0;
NSMutableArray *combinedArr = [[NSMutableArray alloc] init]:
NSInteger count = [arrayDeals count];
for (int i = 0; i < count; i++) {
x++;
CustomObject *customObject = [CustomObject customObjectWithName:[arrayDeals objectAtIndex:i] andNumber:x];
[combinedArr addObject:customObject];
}
To give you some idea of what is wrong with the code you posted:
combinedArr = [[NSMutableArray alloc]initWithObjects:
[CustomObject customObjectWithName:[arrayDeals objectAtIndex:i] andNumber:x],nil];
Here you create a new NSMutableArray to which you assign an new object to taked the object from the array arrayDeals. But you create this NSMutableArray for every item in the array arrayDeals and you assign them to the same variable.
So each iteration you leak the NSMutableArray.
Also :
for (int i=0; i<=[arrayDeals count]-1; i++) {
is the same as
for (int i=0; i < [arrayDeals count]; i++) {
but the count is called every time you iterate, so as per my example I saved the count in a int to just speed things up.
You could even speed the code up using fast Enumeration:
NSInteger x = 0;
NSMutableArray *combinedArr = [[NSMutableArray alloc] init]:
for (id object in arrayDeals) {
id secondObject = [secondArray itemAtIndex:x];
// Arrays start at 0 so only up it after we've got the object.
x++;
CustomObject *customObject = [CustomObject customObjectWithName:object andNumber:x];
[combinedArr addObject:customObject];
}