I'm trying to divide an array into individual arrays of four elements, where the last array will contain the reminder. For example, if that main array's length property will be ten, three subarrays will be created - two consisting of four elements, and one of two elements.
The code I have right now looks like the following:
NSMutableArray *mainMutableArray = [NSMutableArray arrayWithObjects:#"First", #"Second", #"Third", #"Fourth", #"Fifth", #"Sixth", #"Seventh", #"Eighth", nil];
NSMutableArray *mutableArrayOfSubarrays = [NSMutableArray array];
int length = mainMutableArray.count / 4;
int location = 0;
for (int i = 0; i < length; i++)
{
[mutableArrayOfSubarrays addObject:[mainMutableArray subarrayWithRange:NSMakeRange(location, 4)]];
location += 4;
}
This of course works only when the reminder is equal to 0.
Any help would be greatly appreciated.
Ok, here we go:
int length = mainMutableArray.count;
for (int location = 0; location < length; location+=4)
{
unsigned int Size=length-location;
if (Size>4) Size=4;
[mutableArrayOfSubarrays addObject:[mainMutableArray subarrayWithRange:NSMakeRange(location, Size)]];
}
If you use a while loop, you can make the condition describe what you are actually trying to do:
NSUInteger length = [mainMutableArray count];
NSUInteger location = 0;
// Until the location is less than four away from the end
while( location <= (length - 4) ){
[mutableArrayOfSubarrays addObject:[mainMutableArray subarrayWithRange:NSMakeRange(location, 4)]];
location += 4;
}
// Pick up the remainder, if any
if( location != length ){
[mutableArrayOfSubarrays addObject:[mainMutableArray subarrayWithRange:NSMakeRange(location, length-location)]];
}
Loop from length*4 to mainMutableArray.count to get the remainder of the array.
Related
I'm using NSArray/NSMutable array to store different objects.
Once all the objects are added, I want to re-arrange them in random order.
How can I do it?
NSUInteger count = [yourMutableArray count];
for (NSUInteger i = 0; i < count; ++i) {
// Select a random element between i and end of array to swap with.
int nElements = count - i;
int n = (arc4random() % nElements) + i;
[yourMutableArray exchangeObjectAtIndex:i withObjectAtIndex:n];
}
// the Knuth shuffle
for (NSInteger i = array.count-1; i > 0; i--)
{
[array exchangeObjectAtIndex:i withObjectAtIndex:arc4random_uniform(i+1)];
}
Link GameplayKit/GameplayKit.h in your project then
#import <GameplayKit/GameplayKit.h>
Now you can use the property shuffledArray.
NSArray *randomArray = [yourArray shuffledArray];
Swift 4
let count = self.arrayOfData.count
for (index, _) in self.arrayOfData.enumerated()
{
let nTempElement = count - index
let swapIndexwith = (Int(arc4random()) % nTempElement) + index
arrayOfData.swapAt(index, swapIndexwith)
}
This question already has answers here:
iOS: How do I generate 8 unique random integers?
(6 answers)
Closed 9 years ago.
I have 10 UIButtons created in historyboard, OK?
I want to add random numbers that do not repeat these numbers, ie, numbers from 0 to 9 that interspersed whenever the View is loaded.
I tried to find on Google and here a way to use my existing buttons ( 10 UIButton ), and just apply them to random values. Most ways found ( arc4random() % 10 ), repeat the numbers.
Here's one
here's another
here's another
All results found that creating buttons dynamically. Anyone been through this?
Create an array of the numbers. Then perform a set of random swapping of elements in the array. You now have your unique numbers in random order.
- (NSArray *)generateRandomNumbers:(NSUInteger)count {
NSMutableArray *res = [NSMutableArray arrayWithCapacity:count];
// Populate with the numbers 1 .. count (never use a tag of 0)
for (NSUInteger i = 1; i <= count; i++) {
[res addObject:#(i)];
}
// Shuffle the values - the greater the number of shuffles, the more randomized
for (NSUInteger i = 0; i < count * 20; i++) {
NSUInteger x = arc4random_uniform(count);
NSUInteger y = arc4random_uniform(count);
[res exchangeObjectAtIndex:x withObjectAtIndex:y];
}
return res;
}
// Apply the tags to the buttons. This assumes you have 10 separate ivars for the 10 buttons
NSArray *randomNumbers = [self generateRandomNumbers:10];
button1.tag = [randomNumbers[0] integerValue];
button2.tag = [randomNumbers[1] integerValue];
...
button10.tag = [randomNumbers[9] integerValue];
#meth has the right idea. If you wanna make sure the numbers aren't repeating, try something like this: (note: top would the highest number to generate. Make sure this => amount or else this will loop forever and ever and ever ;)
- (NSArray*) makeNumbers: (NSInteger) amount withTopBound: (int) top
{
NSMutableArray* temp = [[NSMutableArray alloc] initWithCapacity: amount];
for (int i = 0; i < amount; i++)
{
// make random number
NSNumber* randomNum;
// flag to check duplicates
BOOL duplicate;
// check if randomNum is already in your array
do
{
duplicate = NO;
randomNum = [NSNumber numberWithInt: arc4random() % top];
for (NSNumber* currentNum in temp)
{
if ([randomNum isEqualToNumber: currentNum])
{
// now we'll try to make a new number on the next pass
duplicate = YES;
}
}
} while (duplicate)
[temp addObject: randomNum];
}
return temp;
}
I have an NSMutableArray urlArray of size n, I want to randomly choose 4 of these URLs from the total number of elements in the array.
However I don't want to shuffle urlArray directly, I'd prefer to make an "indexArray" [0 ... (n-1)] & shuffle these, & then use the first 4 elements of the shuffled indexArray to decide which elements I choose from urlArray.
First off I created the indexArray as follows:
for (int i = 0; i < numberOfStems; i++) {
[indexArray addObject:[NSNumber numberWithInteger:i]];
}
This allowed me to shuffle my indexArray, so far so good. Because I used the
[NSNumber numberWithInteger:i] method, the elements in the shuffled indexArray are NSNumbers.
Is there a way to convert the NSNumber objects in indexArray into ints?
I attempted to use the intValue function but this didn't appear to be what I needed.
I also tried creating a c style array but that wasn't so successful either - I'd like to stick with objective-c syntax if possible.
Any ideas? any hints appreciated :)
Why don't you just create a normal c array, shuffle that and then use the first four integers in the array as the for random index?
something like
int* index = malloc(numberOfStems*sizeof(int));
for (int i = 0; i < numberOfStems; ++i)
{
index[i] = i;
}
for (int i = numberOfStems - 1; i > 0; --i)
{
int randomIndex = arc4random() % i;
int tmp = index[i];
index[i] = index[randomIndex];
index[randomIndex] = tmp;
}
now use index to access the URL's
EDITED: updated algorithm (although not really related to OP question)
For a temporary array that stores only integers and gets thrown away after a relatively short task I would definitely prefer a C-style array: this would avoid a great deal of overhead, and is also simple to read.
int *array = (int*)malloc(sizeof(int)*numberOfStems);
for (int i = 0 ; i != numberOfStems ; i++) {
array[i] = i;
}
// Do the shuffle
// Pick first four, and do whatever you need to do
// ...
// Now that you are done with the array, do not forget to free it:
free(array);
I'm trying to convert a sectionned table into a flat list using this function into didSelectRowAtIndexPath (I have a NSArray that is initialisated with the number of items contained in each section) :
Somewhere... :-)
self.sectionsArray = [NSArray arrayWithObjects:macroIntNumber(1), macroIntNumber(3), macroIntNumber(12), nil];
then into didSelectRowAtIndexPath :
int selectedRow = 0;
int a = indexPath.section;
for (int i=0; i<indexPath.section-1; i++) {
selectedRow += [[self.sectionsArray objectAtIndex:i] intValue];
}
selectedRow += indexPath.row;
But... This crashes for indexPath.section = 0 (first section).
Because the loop is played infinitly until crash of the NSArray call...
Strange !!!
forcing for (int i=0; i<0-1; i++) { works
forcing for (int i=0; i<a-1; i++) { works
What am I missing ?
section is an NSUInteger, so it's unsigned. Thus, subtracting 1 from 0 on that unsigned integer is taking you to a very large number rather than -1.
It works when using a, because you've declared a as an int. :)
I have a C array defined in my method as:
int c = 4;
int r = 5;
keysArray[c][r];
I have this for loop, which works, populating the keysArray as expected.
for (int row = 0; row < r; row++) {
for (int column = 0; column < c; column++){
keysArray[column][row] = [anotherArray objectAtIndex:0];
NSLog(#"array1 %#",keysArray[column][row]);
[anotherArray removeObjectAtIndex:0];
}
}
Then in a for loop underneath, featuring exactly the same looping counter structure, when i try to NSLog the array, it gives an EXC_BAD_ACCESS.
for (int row = 0; row < r; row++){
for (int column = 0; column < c; column++) {
NSLog(#"array2: %#",keysArray[column][row]); //EXC_BAD_ACCESS here
}
}
What would cause this to happen, given that the keysArray is defined in the method body, outside of both sets of loops?
Are the contents of anotherArray retained by some other object? If not, they do not exist anymore in the second loop. WTH are you using a C array to store Objective-C objects anyway?
int c = 4;
int r = 5;
NSMutableArray *keysArray = [[NSMutableArray alloc] initWithCapacity:c];
for (int column = 0; column < c; column++) {
[keysArray addObject:[NSMutableArray arrayWithCapacity:r]];
for (int row = 0; row < r; row++) {
[[keysArray objectAtIndex:column] addObject:[anotherArray objectAtIndex:0]];
[anotherArray removeObjectAtIndex:0];
}
}
for (int row = 0; row < r; row++){
for (int column = 0; column < c; column++) {
NSLog(#"array2: %#", [[keysArray objectAtIndex:column] objectAtIndex:row]);
}
}
You need to retain the objects held in your C array. Unlikes an NS*Array, a C array does not retain on adding to the array.
However, for a no-holes 2D array like that, I'd just use a single NSMutableArray. Any N-dimensional array can be represented as a line-- as a one dimensional array-- with simple math.
Namely, to determine the index of an object at (X,Y), use (Y * width) + X).
The only caveat is that NS*Array does not support "holes". You will need to fill the array row by row. That is, for a 3x4 (3 wide, 4 tall) array, you would fill it in the order 0,0, 1,0, 2,0, 0,1, 1,1, etc...
Obviously, insert and remove operations will mess up your 2D representation (but they would in an NSMutableArray of NSMutableArrays, too).
Alternatively, use NSPointerArray as it can have holes.
Could this be the problem :
[anotherArray removeObjectAtIndex:0];
try
keysArray[column][row] = [[anotherArray objectAtIndex:0] retain];
although if I were you I would use NSMutableArray of NSMutableArray instead