I have an NSArray, and I've calculated a list of integers that represent (in binary) the elements I need to pull out of the array into a new array.
For example, I have 7, 11, and 13, whose bit patterns are 000111, 001011, and 001101. I want to grab three arrays, made of elements 0,1,2, then elements 0,1,3, and then 0,2,3 out of the main array.
Construct an NSIndexSet from the bit patterns you have:
#implementation NSIndexSet (NonContiguous)
+ (instancetype)indexSetFromMask:(NSUInteger)mask
{
NSMutableIndexSet * set = [NSMutableIndexSet indexSet];
for( NSUInteger i = 0; i < (sizeof(NSUInteger) * 8); i++ ){
if( mask & (1l << i) ){
[set addIndex:i];
}
}
return set;
}
#end
Then use objectsAtIndexes:
[origArray objectsAtIndexes:[NSIndexSet indexSetFromMask:7]];
// etc.
Assuming you want the output to be in the form [[a,b,c],[a,b,d],[a,c,d]] for the example, you could do something like this:
NSArray *sourceArray = [[NSArray alloc] initWithObjects:#"a",#"b",#"c",#"d",...,nil];
NSArray *grabArray = [[NSArray alloc] initWithObjects:[NSNumber numberWithInt:7],[NSNumber numberWithInt:11],[NSNumber numberWithInt:13],...,nil];
NSMutableArray *resultArray = [[NSMutableArray alloc] init];
Then for each element of grabArray, add the correct elements to resultArray:
for (NSNumber num in grabArray) {
int n = [num intValue];
int bit = floor(log2(n)); //get highest bit in the current number
NSMutableArray *curr = [[NSMutableArray alloc] init];
while (n>0) {
if (n>pow(bit,2)) { //if this bit is a 1
[curr addObject:[sourceArray objectAtIndex:bit]];
}
n-=pow(bit,2);
bit-=1;
}
[resultArray addObject:curr];
}
Then resultArray should be the array you are looking for. It will add the objects in reverse order, so if order matters you would want to use [curr insertObject: [sourceArray objectAtIndex:bit] atIndex:0]; instead.
Related
I want to create an NSMutableArray of NSMutableArrays. Below is the psuedo code:
NSMutableArray *mapcoords = [[NSMutableArray alloc] init];
NSMutableArray *clustercoords = [[NSMutableArray alloc] init];
while (!FINISHED)
{
for(int j = 1;j <= 4;j++)
{
x = arc4random_uniform(45);
[mapcoords addobject:[NSNumber numberWitInt:x]];
}
[clustercoords addobject:mapcoords];
[mapcoords removeAllObjects];
}
When I inspect the "clustercoords" array at the end of the loop, all of the objects contain the same values. I figured this must be because I am pointing to the same object (mapcoords) every time I add it to clustercoords.
I assume that I would need a different several different "mapcoords" arrays so that the objects in mapccords are unique. Is this the correct assumption? Is there another alternative?
Your assumption is correct. Move the declaration and creation of mapcoords inside the while loop.
NSMutableArray *clustercoords = [[NSMutableArray alloc] init];
while (!FINISHED) {
NSMutableArray *mapcoords = [[NSMutableArray alloc] init];
for(int j = 1; j <= 4; j++) {
u_int32_t x = arc4random_uniform(45);
[mapcoords addObject:#(x)];
}
[clustercoords addObject:mapcoords];
}
What I am trying to achieve, is to convert a csv file into an array of custom objects, however, my attempts at this seem to result in all of the objects in the array being returned as the same object (the last object in the array).
Before I explain further, here is the code:
- (NSArray *)arrayFromCSVFileName:(NSString *)csvFileName fileType:(NSString *)fileType {
// Convert the file into an NSData object
NSString *studentFilePath = [[NSBundle mainBundle] pathForResource:csvFileName ofType:fileType];
NSData *studentData = [NSData dataWithContentsOfFile:studentFilePath];
// Convert the NSData into an NSString
NSString *csvString = [[NSString alloc] initWithData:studentData encoding:NSUTF8StringEncoding];
// Split each record (line) in the csvDataString into an individual array element (split on the newline character \n)
NSArray *csvArray = [csvString componentsSeparatedByString:#"\n"];
// Create an array to hold the parsed CSV data
NSMutableArray *parsedCSVArray = [[NSMutableArray alloc] init];
NSMutableArray *elementArray = [[NSMutableArray alloc] init];
CGSElement *elementToAdd = [[CGSElement alloc] init];
// Loop through each line of the file
for (int i = 0; i < [csvArray count]; i++) {
// Get a reference to this record (line) as a string, and remove any extranous new lines or alike
NSString *csvRecordString = [[csvArray objectAtIndex:i] stringByReplacingOccurrencesOfString:#"\r" withString:#""];
// Split the line by the comma delimeter
NSArray *csvRecordArray = [csvRecordString componentsSeparatedByString:#","];
// Check that there are actually fields (i.e. this is not a blank line)
if ( ([csvRecordArray count] > 0) && ([[csvRecordArray objectAtIndex:0] length] > 0) ) {
elementToAdd.mass = [[csvRecordArray objectAtIndex:1] floatValue];
elementToAdd.atomicNumber = [[csvRecordArray objectAtIndex:0] intValue];
elementToAdd.name = [csvRecordArray objectAtIndex:2];
elementToAdd.symbol = [csvRecordArray objectAtIndex:3];
elementToAdd.period = [[csvRecordArray objectAtIndex:4] intValue];
[elementArray addObject:elementToAdd];
}
}
for (int i = 0; i < [elementArray count]; i++) {
NSLog(#"%i", i);
CGSElement *current = [elementArray objectAtIndex:i];
NSLog(#"Name = %#", current.name);
}
// Return the parsed array
return elementArray;
}
The custom object in question is the CGSElement object, which I am attempting to fill the elementArray with. However, my debug code (the following section of code):
for (int i = 0; i < [elementArray count]; i++) {
NSLog(#"%i", i);
CGSElement *current = [elementArray objectAtIndex:i];
NSLog(#"Name = %#", current.name);
}
Is resulting, rather than in the return of all of the correct element names, it is returning the last element (to put this in context, ununoctium), 118 times.
After some testing, I can safely say that up until after this point:
elementToAdd.mass = [[csvRecordArray objectAtIndex:1] floatValue];
elementToAdd.atomicNumber = [[csvRecordArray objectAtIndex:0] intValue];
elementToAdd.name = [csvRecordArray objectAtIndex:2];
elementToAdd.symbol = [csvRecordArray objectAtIndex:3];
elementToAdd.period = [[csvRecordArray objectAtIndex:4] intValue];
All of the elements are being correctly defined, rather than just the same element over and over.
Needless to say, I'm stumped as to why it would be returning the same object over and over. Any help would be appreciated.
This line:
CGSElement *elementToAdd = [[CGSElement alloc] init];
Should be inside your loop, just before you try to edit the object and add it to the array. Currently you are repeatedly mutating the same object instead of creating new objects for each record.
You add the same entity all the time. It is crated once before the loop and within the loop it values are changed again and angan and it is added to the array. Naturally all items in the aray carry the same values because it is the same object.
If you want then change the array with an NSSet. To a set an object can only added once and you will end up with a set of 1. That is not the solution of couse, it would just visualize what is happening.
To solve it move this line
CGSElement *elementToAdd = [[CGSElement alloc] init];
to the beginning of the body of the for i loop, so that a new instance is created for every iteration and therefore for every index of the array.
I have an NSArray with 17 objects, something like this:
NSArray *objArray = [[NSArray alloc]initWithObjects: #"1",#"2",#"3",#"4",#"5",#"6"
,#"7",#"8",#"9",#"10",#"11",#"12",#"13",#"14",#"15",#"16",#"17", nil];
and an int with a random number as follows:
int random = arc4random()%17+1;
I want to get a random object from this NSArray without it being a duplicate, even if I closed the app (maybe by using NSUserDefaults).
If I've gotten all the objects I want to generate a new random sequence for the same objects.
You could do this by making a mutable copy of the array, and after you make a random selection from that array, remove that same object. When you want to save the array, save the mutable array itself, so can resume where you left off when the app restarts. This little test app does that, and just logs the value of the random pick:
- (void)viewDidLoad {
[super viewDidLoad];
self.objArray = #[#"1",#"2",#"3",#"4",#"5",#"6",#"7",#"8",#"9",#"10",#"11",#"12",#"13",#"14",#"15",#"16",#"17"];
self.mut = [self.objArray mutableCopy];
}
-(IBAction)pickNumber:(id)sender {
int index = arc4random_uniform(self.mut.count);
NSLog(#"%#", self.mut[index]);
[self.mut removeObjectAtIndex:index];
if (self.mut.count == 0) {
self.mut = [self.objArray mutableCopy];
NSLog(#"*******************");
}
}
As a starting point, you could shuffle your array:
+ (NSArray *)arrayByShufflingArray:(NSArray *)array
{
// Fisher-Yates algorithm
NSMutableArray *result = [array mutableCopy];
NSUInteger count = [result count];
for (NSInteger i = ((NSInteger) count) - 1; i > 0; i--) {
NSUInteger firstIndex = (NSUInteger)i;
NSUInteger secondIndex = arc4random() % (NSUInteger)(i + 1);
[result exchangeObjectAtIndex:firstIndex withObjectAtIndex:secondIndex];
}
return result;
}
Step through each shuffled element and when you get to the end, reshuffle.
It can still happen that an item is selected twice in a row when the last item of one shuffle is the same as the first item in the next shuffle. If you want to avoid this you'll have to add some additional code.
Just Copy and Paste
-(NSMutableArray*)getRandomValueFromArray:(NSMutableArray*)arrAllData randomDataCount:(NSInteger)count {
NSMutableArray *arrFilterData = [[NSMutableArray alloc]init];
for(int i=0; i<count; i++){
NSInteger index = arc4random() % (NSUInteger)(arrAllData.count);
[arrFilterData addObject:[arrAllData objectAtIndex:index]];
[arrAllData removeObjectAtIndex:index];
}
return arrFilterData;
}
Note: count = number of random values you want to fetch from array.
How can I save the string that match from one NSArray with one index difference in NSMutableArray?
For example, there are three "apple", four "pineapple", six "banana", two "cocoa" and the rest of words dont have duplicate(s) in the nsarray, i would like to know if the nsarray has at least two same words. If yes, I would like to save "apple", "pineapple, "banana" and "cocoa" once in nsmutablearray. If there are other alike words, I would like to add them to namutablearray too.
My code (which still doesn't work properly);
NSArray *noWords = [[NSArray alloc] initWithArray:
[[NSString stringWithContentsOfFile:[[NSBundle mainBundle]
pathForResource:#"words" ofType:#"txt"]
encoding:NSUTF8StringEncoding error:NULL]
componentsSeparatedByString:#"\n"]];
NSUInteger scount = [noWords count];
int ii = 0;
NSString *stringline;
for (ii; ii < scount; ii++)
{
stringline = [noWords objectAtIndex:ii];
NSLog(#"stringline : %# ", stringline);
}
int i = 1;
NSString *line;
for (i ; i < 10; i++)
{
line = [noWords objectAtIndex:i];
NSLog (#"line : %# ", line);
NSMutableArray *douwords = [NSMutableArray array];
if ([stringline isEqualToString:line])
{
NSString *newword;
for (newword in douwords)
{
[douwords addObject:newword];
NSLog (#"detected! %# ", douwords);
}
}
}
Here's a solution using two sets:
- (NSArray *)getDuplicates:(NSArray *)words
{
NSMutableSet *dups = [NSMutableSet set],
*seen = [NSMutableSet set];
for (NSString *word in words) {
if ([seen containsObject:word]) {
[dups addObject:word];
}
[seen addObject:word];
}
return [dups allObjects];
}
Assuming NSSet uses hash tables behind the scenes (which I'm betting it does), this is going to be faster than the previously suggested O(n^2) solution.
Here's something off the top of my head:
NSMutableSet* duplicates = [NSMutableSet set];
NSArray* words = [NSArray arrayWithObjects:#"Apple", #"Apple", #"Orange", #"Apple", #"Orange", #"Pear", nil];
[words enumerateObjectsUsingBlock:^(NSString* str, NSUInteger idx, BOOL *stop) {
for (int i = idx + 1; i < words.count; i++) {
if ([str isEqualToString:[words objectAtIndex:i]]) {
[duplicates addObject:str];
break;
}
}
}];
NSLog(#"Dups: %#", [duplicates allObjects]); // Prints "Apple" and "Orange"
The use of an NSSet, as opposed to an NSArray, ensures strings are not added more than once. Obviously, there are optimizations that could be done, but it should be a good starting point.
I assume that you want to count appearances of words in your array and output those with a count of more than one. A basic and verbose way to do that would be:
// Make an array of words - some duplicates
NSArray *wordList = [[NSArray alloc] initWithObjects:
#"Apple", #"Banana", #"Pencil",
#"Steve Jobs", #"Kandahar",
#"Apple", #"Banana", #"Apple",
#"Pear", #"Pear", nil];
// Make an mutable dictionary - the key will be a word from the list
// and the value will be a number representing the number of times the
// word appears in the original array. It starts off empty.
NSMutableDictionary *wordCount = [[NSMutableDictionary alloc] init];
// In turn, take each word in the word list...
for (NSString *s in wordList) {
int count = 1;
// If the word is already in the dictionary
if([wordCount objectForKey:s]) {
// Increse the count by one
count = [[wordCount objectForKey:s] intValue] + 1;
}
// Save the word count in the dictionary
[wordCount setObject:[NSNumber numberWithInt:count] forKey:s];
}
// For each word...
for (NSString *s in [wordCount keysOfEntriesPassingTest:
^(id key, id obj, BOOL *stop) {
if ([obj intValue] > 1) return YES; else return NO;
}]) {
// print the word and the final count
NSLog(#"%2d %#", [[wordCount objectForKey:s] intValue], s);
}
The output would be:
3 Apple
2 Pear
2 Banana
How would I create a number of NSDictionary variables using an array's count?
This is basically what I came up with, but I'm not sure how to make this work with Objective-C syntax. doesntContainAnother is an NSArray. I want the names of the dictionaries to use the current value of loopInt.
int *loopInt = 0;
while (doesntContainAnother.count <= loopInt) {
NSMutableDictionary *[NSString stringWithFormat:#"loopDictionary%i", loopInt] = [[[NSMutableDictionary alloc] init] autorelease];
[NSString stringWithFormat:#"loopDictionary%i", loopInt] = [NSDictionary dictionaryWithObject:[array1 objectAtIndex:loopInt]
forKey:[array2 objectAtIndex:loopInt]];
loopInt = loopInt + 1;
}
Create a mutable array and loop until you reach the original array's count, creating a dictionary and adding it to the mutable array on each iteration.
Your code should look like this.
NSMutableArray *dictionaries = [[NSMutableArray alloc] init];
for (int i = 0; i < doesntContainAnother.count; i++) {
[dictionaries addObject:[NSMutableDictionary dictionaryWithObject:[array1 objectAtIndex:i] forKey:[array2 objectAtIndex:i]]];
}
The approach of creating variables with numbers at the end of their names is an antipattern and not even possible in Objective-C. It's equivalent to an array, but clunkier.
You need to create a mutable array, and then put the objects into the array. You can't create a variable with the same name as the contents of a string, as you have done. For example:
NSMutableArray *arr = [[NSMutableArray alloc] initWithCapacity:[doesntContainAnother count]];
int i = 0; // Note: type is int, not int*
for (i = 0; i < [doesntCountainAnother count]; i++) {
[arr addObject:[NSMutableDictionary dictionary]];
}
// Later...
NSMutableDictionary *d1 = [arr objectAtIndex:3];
Or if you want to pull them out of the list by name:
NSMutableDictionary *dict = [[NSMutableDictionary alloc] initWithCapacity:[doesntCountainAnother count]];
int i = 0;
for (i = 0; i < [doesntContainAnother count]; i++) {
[dict setObject:[NSMutableDictionary dictionary] forKey:[NSString stringWithFormat:#"loopDictionary%d", i]];
}
// Later...
NSMutableDictionary *d1 = [dict objectForKey:#"loopDictionary3"];
But the first way is likely the easiest.