I'm trying to use NSRange to hold a range of years, such as
NSRange years = NSMakeRange(2011, 5);
I know NSRange is used mostly for filtering, however I want to loop over the elements in the range. Is that possible without converting the NSRange into a NSArray?
It kind of sounds like you're expecting NSRange to be like a Python range object. It's not; NSRange is simply a struct
typedef struct _NSRange {
NSUInteger location;
NSUInteger length;
} NSRange;
not an object. Once you've created one, you can use its members in a plain old for loop:
NSUInteger year;
for(year = years.location; year < NSMaxRange(years); year++ ){
// Do your thing.
}
(Still working on the assumption that you're thinking about Python.) There's syntax in ObjC called fast enumeration for iterating over the contents of an NSArray that is pleasantly similar to a Python for loop, but since literal and primitive numbers can't be put into an NSArray, you can't go directly from an NSRange to a Cocoa array.
A category could make that easier, though:
#implementation NSArray (WSSRangeArray)
+ (id)WSSArrayWithNumbersInRange:(NSRange)range
{
NSMutableArray * arr = [NSMutableArray array];
NSUInteger i;
for( i = range.location; i < NSMaxRange(range); i++ ){
[arr addObject:[NSNumber numberWithUnsignedInteger:i]];
}
return arr;
}
Then you can create an array and use fast enumeration:
NSArray * years = [NSArray WSSArrayWithNumbersInRange:NSMakeRange(2011, 5)];
for( NSNumber * yearNum in years ){
NSUInteger year = [yearNum unsignedIntegerValue];
// and so on...
}
Remember that a NSRange is a structure holding two integers, representing the start and length of the range. You can easily loop over all of the contained integers using a for loop.
NSRange years = NSMakeRange(2011, 5);
NSUInteger year;
for(year = years.location; year < years.location + years.length; ++year) {
// Use the year variable here
}
This is a bit of an old question, but an alternative to using an NSArray would be to create an NSIndexSet with the desired range (using indexWithIndexesInRange: or initWithIndexesInRange:) and then using block enumeration as in https://stackoverflow.com/a/4209289/138772. (Seemed relevant as I was just checking on this myself.)
My alternate solution for this, was to define a macro just to make shorthand quicker.
#define NSRangeEnumerate(i, range) for(i = range.location; i < NSMaxRange(range); ++i)
To call it you do:
NSArray *array = #[]; // must contain at least the following range...
NSRange range = NSMakeRange(2011, 5);
NSUInteger i;
NSRangeEnumerate(i, range) {
id item = array[i];
// do your thing
}
personally I am still trying to figure out how I can write the macro so I can just call it like:
NSRangeEnumerate(NSUInteger i, range) {
}
which is not supported just yet... hope that helps or makes typing your program quicker
Related
Question:
Find the value of K in myInterViewArray without any messages/calls
I was given this hint:
The numbers in the array will never exceed 1-9.
NSArray *myInterViewArray = #[#2,#1,#3,#9,#9,#8,#7];
Example:
If you send 3, the array will return the 3 biggest values in myInterViewArray * 3. So in the example below, K = 9 + 9 + 8.
--
I was asked this question a while back in an interview and was completely stumped. The first solution that I could think of looked something like this:
Interview Test Array:
[self findingK:myInterViewArray abc:3];
-(int)findingK:(NSArray *)myArray abc:(int)k{ // With Reverse Object Enumerator
myArray = [[[myArray sortedArrayUsingSelector:#selector(compare:)] reverseObjectEnumerator] allObjects];
int tempA = 0;
for (int i = 0; i < k; i++) {
tempA += [[myArray objectAtIndex:i] intValue];
}
k = tempA;
return k;
}
But apparently that was a big no-no. They wanted me to find the value of K without using any messages. That means that I was unable to use sortedArrayUsingSelector and even reverseObjectEnumerator.
Now to the point!
I've been thinking about this for quite a while and I still can't think of an approach without messages. Does anyone have any ideas?
There is only one way to do that and that is bridging the array to CF type and then use plain C, e.g.:
NSArray *array = #[#1, #2, #3];
CFArrayRef cfArray = (__bridge CFArrayRef)(array);
NSLog(#"%#", CFArrayGetValueAtIndex(cfArray, 0));
However, if the value is a NSNumber, you will still need messages to access its numeric value.
Most likely the authors of the question didn't have a very good knowledge of the concept of messages. Maybe they thought that subscripting and property access were not messages or something else.
Using objects in Obj-C without messages is impossible. Every property access, every method call, every method initialization is done using messages.
Rereading the question, they probably wanted you to implement the algorithm without using library functions, e.g. sort (e.g. you could implement a K-heap and use that heap to find the K highest numbers in a for iteration).
I assume what is meant is that you can't mutate the original array. Otherwise, that restriction doesn't make sense.
Here's something that might work:
NSMutableArray *a = [NSMutableArray array];
for (NSNumber *num in array) {
BOOL shouldAdd = NO;
for (int i = a.count - 1; i >= k; i--) {
if ([a[i] intValue] < [num intValue]) {
shouldAdd = YES;
break;
}
}
if (shouldAdd) {
[a addObject:num];
}
}
int result = a[a.count - k];
for (int i = k; k < a.count; k++) {
result += [a[i] intValue];
}
return result;
I am new in Objective-C and have been using NSRange most of the time in my code.
I have just came to know that there is NSMakeRange. So, I just want to know - what is the use of NSMakeRange?
It's a convenience inline function, used to create an NSRange struct, populate it and return it:
(from .../Foundation.framework/Headers/NSRange.h)
NS_INLINE NSRange NSMakeRange(NSUInteger loc, NSUInteger len) {
NSRange r;
r.location = loc;
r.length = len;
return r;
}
It makes it simpler to create ranges; compare:
unichar buffer[8];
[someString getCharacters:buffer range:NSMakeRange(2, 8)];
to:
unichar buffer[8];
NSRange range = { 2, 8 };
[someString getCharacters:buffer range:range];
It's just a convenience function. It allows you to replace this:
NSRange r;
r.location = 1;
r.length = 2;
DoSomething(r);
with this:
DoSomething(NSMakeRange(1, 2));
NSMakeRange(5, 1) creates a range with location 5 and length 1. See the documentation for further information and related functions.
Alt-click the function name in Xcode, you’ll get a reference.
Well, it's to make range with specified two values. Some of the Objective-C APIs will require you to use this.
From Apple's documentation:
A structure used to describe a portion of a series—such as characters
in a string or objects in an NSArray object.
typedef struct _NSRange {
NSUInteger location;
NSUInteger length; } NSRange;
There are many ways of creating a NSRange object,
1 - using NSMakeRange
NSRange range = NSMakeRange(10, 50);
2 - By specifying within {}
NSRange range = {10,50};
3 - By properties
NSRange range;
range.location = 10;
range.length = 50;
Using either won't make much difference, but using NSMakeRange will definitely make your code more readable.
I'm writing a for in loop to read a list of names from an NSArray, here is my code.
NSArray *names = [NSArray arrayWithObjects:#"Luke",#"James",#"Fred",#"Harry", nil];
for (NSString *name in names) {
NSLog(#"%#",name);
}
What I am trying to determine is wether there is an easier way to get the current loop number without adding a variable outside the loop like so..
int number = 0;
for (NSString *name in names) {
number++;
NSLog(#"%i - %#",number,name);
}
Is there a built in 'loop number' property that can be accessed during a for loop? - Am I barking up the wrong tree? Should I just use the variable and get over it?
What you've done is reasonable (although I'd put number++ at the end of the loop). Usually when I need a loop index, I avoid fast enumeration and use a more traditional for loop:
for (NSUInteger i=0; i<[names count]; i++) {
NSString *name = names[i];
NSLog(#"%i - %#", i, name);
}
If you need the index, use a standard 3-part for loop, or the number counter with a while loop. No way to magically get the index in the for...in style loop.
This seems quite a bit of a hack. You could either use a normal for loop instead of fast enumeration, or enumerate the objects using a block, or you can also use the indexOfObject: method inside the for loop (but this is really discouraged since it works only if you have only unique objects in the array, and anyways the repeated lookup makes it slower). All in all, try this:
int i;
for (i = 0; i < names.count; i++) {
NSString *name = [names objectAtIndex:i];
// and "i" already stores the index
}
or this:
[names enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
// use obj and idx
}];
and this is also possible, but don't do it:
for (NSString *name in names) {
int idx = [names indexOfObject:name];
// etc.
}
I've been trying to figure out a way of checking how many of a certain object are in an NSArray.
I've looked through the docs and I'm pretty sure there is no premade method for this. Also I can't find anything here on SO.
Do anybody know about a good way to do this? Because I seriously can't come up with anything.
In this specific case I have an array with strings (most cases several of each) and I want to count how many strings in the array that matches to whatever I ask for.
If this is a primary use of the data structure and order doesn't matter, consider switching to an NSCountedSet which is specifically for solving this problem efficiently.
If you need an ordered collection, and you don't have a huge set of objects, than the fast enumeration answers are the best approach.
If you want to know where the objects are, then use indexesOfObjectsPassingTest:.
If you have a huge number of object, I would look at indexesOfObjectsWithOptions:passingTest: with the NSEnumerationConcurrent option. This will allow you to search the array on multiple cores. (This is only possibly faster on a multi-core device, and even then is probably only faster if you have a very large collection. You should absolutely test before assuming that concurrent will be faster.) Even if you just need the final count, it may be faster for certain data sets to use this method and then use count on the final index set.
There actually is a method for this: - (NSIndexSet *)indexesOfObjectsPassingTest:(BOOL (^)(id obj, NSUInteger idx, BOOL *stop))predicate
NSIndexSet *indexes = [array indexesOfObjectsPassingTest:^(id obj, NSUInteger index, BOOL *stop) {
return [obj isEqualTo:myOtherObject];
}];
Sounds like a case for NSCountedSet, which does what you are after with its initWithArray: initializer:
// Example array of strings
NSArray *array = [NSArray arrayWithObjects:
#"Joe", #"Jane", #"Peter", #"Paul",
#"Joe", #"Peter", #"Paul",
#"Joe",
#"Jane", #"Peter",
nil];
NSCountedSet *countedSet = [[NSCountedSet alloc] initWithArray: array];
// for-in will let you loop over the counted set
for (NSString *str in countedSet) {
NSLog(#"Count of %#: %ld", str, (long)[countedSet countForObject:str]);
}
One approach would be to iterate and check.
- (int)repeatsOf:(NSString *)repeater inArray:(NSArray *)array {
int count = 0;
for (NSString *item in array) {
if ([item isEqualToString:repeater]) {
count++;
}
}
return count;
}
You could try a simple loop. Suppose needle is your reference string and array is your NSArray of strings:
unsigned int n = 0;
for (NSString * str in array)
{
if ([needle isEqualToString:str])
{
++n;
}
}
Now n holds the count of strings in equal to needle.
You could define a function like this:
- (int)countStringsThatMatch:(NSString*)match inArray:(NSArray*)array
{
int matches = 0;
for (id string in array) {
if ([string isEqualToString:match]) {
matches++;
}
}
return matches;
}
And then use it like:
int count = [self countStringsThatMatch:#"someString" inArray:someArray];
- (NSUInteger) objectCountInArray:(NSArray *)array
matchingString:(NSString *)stringToMatch {
NSUInteger count = 0;
for (NSString *string in array) {
count += [string isEqualToString:stringToMatch] ? 1 : 0;
}
return count;
}
You can try to expand this to use a block that gets an object and returns a BOOL. Then you can use it to compare an array of whatever you want.
I need to call a cpp function like
void myFunc(float **array2D, int rows, int cols)
{
}
within an objective-c object. Basically, the array is created in my objective-c code as I create an NSArray object. Now, the problem is how to pass this array to my cpp function.
I am a bit new to these mixed c++/objective-c stuffs so any hint will be highly appreciated.
Thanks
I guess you have to convert the NSArray to a plain C array.
Something like:
NSArray *myNSArray; // your NSArray
int count = [myNSArray count];
float *array = new float[count];
for(int i=0; i<count; i++) {
array[i] = [[myNSArray objectAtIndex:i] floatValue];
}
or, as a commenter suggested (assuming your NSArray contains NSNumbers):
NSArray *myNSArray; // your NSArray
int count = [myNSArray count];
float *array = new float[count];
int i = 0;
for(NSNumber *number in myNSArray) {
array[i++] = [number floatValue];
}
Look at this post.
Check out the answer that mentions using [NSArray getObjects] to create a c-style array.
Here's the code that the poster put in there:
NSArray *someArray = /* .... */;
NSRange copyRange = NSMakeRange(0, [someArray count]);
id *cArray = malloc(sizeof(id *) * copyRange.length);
[someArray getObjects:cArray range:copyRange];
/* use cArray somewhere */
free(cArray);
Alternately, since CFArray is toll-free bridged to NSArray, could you call those C functions from your C++ function? I'd look around, wouldn't be surprised if there weren't a C++ wrapper to give similar semantics, or one could be written easily enough.