I need to search a mutable array for the maximum value and return its position as well as value. I'd only like to iterate through the array once and I'm not sure if that's possible
an example of what I'm trying to accomplish can be demonstrated below
NSMutableArray *array = [[NSMutableArray alloc] init];
for (int i = 0; i<20; i++)
[array addObject:[NSNumber numberWithInteger:(arc4random()%200)]];
NSObject *max = [array valueForKeyPath:#"#max.self"];
the max object only seems to contain the value (and not the position). this can be demonstrated through the debugger with print-object max
Any advice out there?
Using valueForKeyPath:#"#max.self" is great, but only if you want the maximum value.
To know both index and value in one iteration, I'd use enumerateWithBlock:
NSMutableArray *array = [[NSMutableArray alloc] init];
for (int i = 0; i<20; i++)
[array addObject:[NSNumber numberWithInteger:(arc4random()%200)]];
__block NSUInteger maxIndex;
__block NSNumber* maxValue = [NSNumber numberWithFloat:0];
[array enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
NSNumber* newValue = obj;
if ([newValue isGreaterThan:maxValue]) {
maxValue = newValue;
maxIndex = idx;
}
}];
Quite more code, but you're iterating only once in the array.
If you're not worried about the possibility of there being more than one identical maximum value in the array, you can use -indexOfObject: to get the index. It will return the first occurrence of the object in the array.
NSUInteger index = [array indexOfObject:max];
I hope, following solution will help you to identify maximum value from array.
int max = [[numberArray valueForKeyPath:#"#max.intValue"] intValue];
NSLog(#"Highest number: %i",max);
Please let me know if any issue.
Here you can find correct way to deal with collections and KVC
Its nice Post by Matt
http://nshipster.com/kvc-collection-operators/
Related
i'm just starting out with Xcode and need some help. I have this array set up:
myArray = [NSMutableArray arrayWithObjects: item1type1, item1type, item1type3, item1type4, item1type5, item1type6, item1type7, item1type8, item1type9, nil];
Is it possible to auto-assign numbers to elements in a sequence? The logic is simple: item1type(i), item1type(i+1), item1type(i+2),...
Many thanks
There are too many magic numbers in this code, but here you go:
// Build an Array of keys #[#"item_1_type_1", #"item_1_type_2", ..., #"item_1_type_9"] programmatically
const int numberOfElements = 9;
NSMutableArray *keys = [NSMutableArray arrayWithCapacity:numberOfElements];
for (int i = 1; i <= numberOfElements; i++) {
[keys addObject:[NSString stringWithFormat:#"item_1_type_%d", i]];
}
// Extract chosen keys from JSON Dictionary into an Array, matching the
// order of the keys above.
NSDictionary *subDict = myJSONData[#"item1"];
NSArray *myArray = [subDict objectsForKeys:keys notFoundMarker:[NSNull null]];
How do you get the index of the number appearing from the arc4rand method?. If 4,1,2,3 appear how do you index them . Example 4 would be 0 in the array.
int rand=((arc4random()%4)+1);
For getting random number, i did like this:
Suppose, i have a mutable array
NSMutableArray * myArray = [[NSMutableArray alloc] init];
and i kept 5 data in this myArray.
Now I have to generate random number index from myArray.
int randomIndex = (arc4random() % ([myArray count]));
Here randomIndex is random index of array
try this one. you need to put all that values into array.
NSMutableArray * array = [[NSMutableArray alloc] initWithCapacity:4];
[array insertObject:#"4" atIndex:0];
[array insertObject:#"1" atIndex:1];
[array insertObject:#"2" atIndex:2];
[array insertObject:#"3" atIndex:3];
using array to get index in ios to add all values in array like this
//convert int to nsstring and add array
NSArray *array=[NSArray arrayWithObjects:NSStringFromInt(4),NSStringFromInt(1),NSStringFromInt(2),NSStringFromInt(3), nil];
//reverse process to get int value
int value=[[array objectAtIndex:index]integerValue];
I'm just guessing, you might look for this...
NSMutableArray *_array = [NSMutableArray array];
for (int i = 0; i < 10; i++) {
[_array addObject:#((arc4random()%4)+1)];
}
Is there a nicer way to fill an array with numbers than what I use?
It's crazy how much I got to write just to fill an array with numbers so they can be used for a calculation in a loop. This is easier in other C based languages like PHP, As3, or Java.
NSArray *myArray = [NSArray arrayWithObjects:
[NSNumber numberWithInt:1000],[NSNumber numberWithInt:237], [NSNumber numberWithInt:2673], nil];
int total = 0;
for(int i = 0; i < [myArray count]; i += 1 ){
total += [[myArray objectAtIndex: i]intValue];
NSLog(#"%i", total);
}
Hopefully there is a shorter way... I just want to fill an array with ints... cant be that hard
I guess you have to use NSNumber for an NSArray. If you want to use ints I guess you'd have to use a c array:
NSInteger myArray[20];
for (int i=0;i<20;i++) {
int num=myArray[i];
//do something
}
NSNumber though is I guess the better approach for this language.
At least you can do fast enumeration to shorten code a bit:
for (NSNumber *n in myArray) {
int num = [n intValue];
//do something....
}
EDIT:
The question has been asked 3 years ago. There have been new literals established to make it easier to create objects like NSNumbers or NSArrays:
NSNumber *n = #100;
or
NSArray *array = #[#100,#50,#10];
Nice short alternative for looping specific integers:
NSArray *numbers = [#"1000,237,2673" componentsSeparatedByString:#","];
for (NSString *i in numbers) {
[i intValue]; // Do something.
}
First start with a C array:
NSInteger myCArray = { 1000, 237, 2673 };
// calculate number of elements
NSUInteger myCArrayLength = sizeof(myCArray) / sizeof(NSInteger;
Second, if you need an NSArray loop through this array and create one:
NSMutableArray *myNSArray = [NSMutableArray arrayWithCapacity:myCArrayLength];
for(NSUInteger ix = 0; ix < myCArrayLength; ix++)
[myNSArray addObject:[NSNumber numberWithInteger:myCArray[ix]];
You can wrap the second piece of code up as a category on NSArray if you're doing it a lot.
too late. but u can do the following too.
int total = 0;
nsarray *myArray = #[#1.8,#100,#299.8];
for(nsnumber *num in myArray){
total+=num;
}
I'm doing this:
for(int i=0;i>count;i++)
{
NSArray *temp=[[NSArray alloc]initWIthObjects]i,nil];
NSLog(#"%i",temp);
}
It returns to me 0,1,2,3....counting one by one, but I want an array with appending these values {0,1,2,3,4,5...}.
This is not a big deal, but I'm unable to find it. I am new to iPhone.
NSMutableArray *myArray = [NSMutableArray array];
for(int i = 0; i < 10; i++) {
[myArray addObject:#(i)];
}
NSLog(#"myArray:\n%#", myArray);
This code is not doing what you want it to do for several reasons:
NSArray is not a "mutable" class, meaning it's not designed to be modified after it's created. The mutable version is NSMutableArray, which will allow you to append values.
You can't add primitives like int to an NSArray or NSMutableArray class; they only hold objects. The NSNumber class is designed for this situation.
You are leaking memory each time you are allocating an array. Always pair each call to alloc with a matching call to release or autorelease.
The code you want is something like this:
NSMutableArray* array = [[NSMutableArray alloc] init];
for (int i = 0; i < count; i++)
{
NSNumber* number = [NSNumber numberWithInt:i]; // <-- autoreleased, so you don't need to release it yourself
[array addObject:number];
NSLog(#"%i", i);
}
...
[array release]; // Don't forget to release the object after you're done with it
My advice to you is to read the Cocoa Fundamentals Guide to understand some of the basics.
A shorter way you could do is:
NSMutableArray *myArray = [NSMutableArray array];
for(int i = 0; i < 10; i++) {
[myArray addObject:#(i)];
}
NSLog(#"myArray:\n%#", myArray);
I used to be a Java Programmer, which the array need to declare the very first time, like this:
int[] anArray; // declares an array of integers
anArray = new int[10]; // allocates memory for 10 integers
I don't know whether the Objective C , NSMutableArray also give me this ability or not. Actually, I want to make a 10*10 array. thz in advance.
I try to do this:
myArray = [[NSMutableArray alloc] initWithCapacity:10];
for (int i=0; i<10; i++) {
myArray[i] = [[NSMutableArray alloc] initWithCapacity:10];
}
But it occurs errors, telling my incompatible type assignment.
The capacity field is seldom useful. The array will be expanded on demand anyway.
And the capacity field just tells the array how much memory you may use. The array's length is still 0.
But you can grow the array from empty:
for (int i = 0; i < 10; ++ i)
[myArray addObject:…];
To read and write to an element in an NSMutableArray, you need:
id x = [array objectAtIndex:i]; // x = array[i];
[array replaceObjectAtIndex:i withObject:y]; // array[i] = y;
You cannot subscript an NSArray directly.
Your code has memory leak. Unlike Java, ObjC doesn't use a GC unless you explicitly enable it (and ObjC on iPhoneOS doesn't have GC). ObjC manages memory by manual reference counting. Basically you need to ensure the ref count of stuff you don't own doesn't change in the process. See http://developer.apple.com/mac/library/documentation/cocoa/Conceptual/MemoryMgmt/MemoryMgmt.html for detail.
In your case, [[NSMutableArray alloc] …]; creates an object of ref count +1, then the assignment will take over the array, that means you don't own it any more, but the ref count is not balanced to 0, so this memory will not be properly deallocated. You need to use convenient methods such as [NSMutableArray array…] to create an object with ref count 0.
NSArray's can only store ObjC objects. int in C (ObjC) is a primitive, and cannot be stored into an NSArray. You have to box it into an NSNumber by [NSNumber numberWithInt:0]. You can get back the integer with -intValue.
To conclude, your code needs to be modified as:
-(NSMutableArray*)get10x10Array {
NSMutableArray* arr = [NSMutableArray array];
for (int i = 0; i < 10; ++ i) {
NSMutableArray* subarr = [NSMutableArray array];
for (int j = 0; j < 10; ++ j)
[subarr addObject:[NSNumber numberWithInt:0]];
[arr addObject:subarr];
}
return arr;
}
But ObjC is a superset of C. You can just use a plain 10x10 C array.
int arr[10][10];
You want a 10x10 array -- of what?
myArray = [[NSMutableArray alloc] initWithCapacity:10];
for (int i=0; i<10; i++) {
myArray[i] = [[NSMutableArray alloc] initWithCapacity:10];
}
But it occurs errors, telling my
incompatible type assignment.
Because you can't assign to myArray like that. myArray is an object that represents an array data structure. It is not a C array.
If you want a 10x10 array of a primitive data type, you can declare one like you would in C:
int myArray[10][10];
initWithCapacity: is what you want. It may look like
NSMutableArrat *array = [[NSMutableArray alloc] initWithCapacity:10];
You can't access Cocoa array objects with the bracket notation. Your second bit of code should be:
NSMutableArray *myArray = [[NSmutableArray alloc] initWithCapacity:10];
for (int i = 0; i < 10; i++) {
[myArray insertObject:[NSMutableArray arrayWithCapacity:10] atIndex:i]; // Note: not using myArray[i]!
}
There are two ways to do this.
Plain old C
If you want to store objects, you should use the id type instead of int.
int myarray[10][10];
myarray[5][2] = 412;
Objective-C
NSArray's are not meant to have spaces without objects, if you need them you could use [NSNull null], but if that's the case a C array would be better anyway.
NSMutableArray *myArray = [[NSMutableArray alloc] initWithCapacity:10];
for (int i=0; i < 10; i++) {
NSMutableArray *innerArray = [[NSMutableArray alloc] initWithCapacity:10];
for (int j=0; j < 10; j++) {
[innerArray addObject:[NSNull null]];
}
[myArray addObject:innerArray];
[innerArray release];
}
[[myArray objectAtIndex:5]
replaceObjectAtIndex:2 withObject:[NSNumber numberWithInteger:123]];
NSArray objects have a fixed size that cannot be changed once they have been initialised. NSMutableArray objects can change size. A 10×10 array is sometimes implemented as an NSArray containing 10 individual NSArray objects, each of these containing ten items. This quickly gets cumbersome, sometimes it is easier to resort back to plain C for such a task:
int tenByTen[10][10];
Or, you can use this:
typedef struct
{
int y[10];
} TenInts;
typedef struct
{
TenInts x[10];
} TenByTen;
Then you could do:
- (void) doSomethingWithTenByTen:(const TenByTen) myMatrix
{
NSLog ("%d", myMatrix.x[1].y[5]);
}
And you can also return them from methods:
- (TenByTen) mangleTenByTen:(const TenByTen) input
{
TenByTen result = input;
result.x[1].y[4] = 10000;
return result;
}
You want NSMutableArray +arrayWithCapacity:
Note that setting the initial capacity is merely an optimization - Mutable arrays expand as needed.
EDIT:
To do the 10x10 case,
myArray = [[NSMutableArray alloc] initWithCapacity:10];
for (int i=0; i<10; i++) {
NSMutableArray *subArray = [NSMutableArray arrayWithCapacity:10];
[myArray addObject:subArray];
for (int j = 0; j<10; j++) {
[subArray addObject:[NSNumber numberWithInt:0]];
}
}
Notes:
an array retains the objects added to it, so its not necessary to retain subArray
only objects (not primitive types like "int") can be added to an NSArray, hence the need for NSNumber numberWithInt:
you use methods like objectAtIndex: and replaceObjectAtIndex:withObject: to get/set a value from an NSArray, not array subscript ([]) syntax
See Apple refs for NSArray and NSMutableArray
You can use the following code to resize the NSMutableArray once it was created:
#interface NSMutableArray (Resizing)
- (NSMutableArray *)resize:(NSInteger)newSize;
#end
#implementation NSMutableArray (Resizing)
- (NSMutableArray *)resize:(NSInteger)newSize
{
int size = (newSize > [self count]) ? self.count : newSize;
NSMutableArray *array = [NSMutableArray arrayWithCapacity:size];
for (int i = 0; i < size; i++){
[array addObject:[self objectAtIndex:i]];
}
return array;
}
#end