Randomly select x amount of items in a "list" - objective-c

Question

I would like to select x amount of items randomly from a "list" in objective C store them in an other "list" (each item can only be selected one) , I'm talking about lists because I'm coming from Python. What would be the best way to store a list of strings in Objective C ?
cheers,

Answer 1

You should use NSMutableArray class for changeable arrays or NSArray for non-changeable ones.
UPDATE: a piece of code for selecting a number of items from an array randomly:
NSMutableArray *sourceArray = [NSMutableArray array];
NSMutableArray *newArray = [NSMutableArray array];
int sourceCount = 10;
//fill sourceArray with some elements
for(int i = 0; i < sourceCount; i++) {
[sourceArray addObject:[NSString stringWithFormat:#"Element %d", i+1]];
}
//and the magic begins here :)
int newArrayCount = 5;
NSMutableIndexSet *randomIndexes = [NSMutableIndexSet indexSet]; //to trace new random indexes
for (int i = 0; i < newArrayCount; i++) {
int newRandomIndex = arc4random() % sourceCount;
int j = 0; //use j in order to not rich infinite cycle
//tracing that all new indeces are unique
while ([randomIndexes containsIndex:newRandomIndex] || j >= newArrayCount) {
newRandomIndex = arc4random() % sourceCount;
j++;
}
if (j >= newArrayCount) {
break;
}
[randomIndexes addIndex:newRandomIndex];
[newArray addObject:[sourceArray objectAtIndex:newRandomIndex]];
}
NSLog(#"OLD: %#", sourceArray);
NSLog(#"NEW: %#", newArray);