Reversing "columns" in a table made from a NSArray - objective-c

Question

I have a NSArray made out of numbers 1..50, which represents a table with columns & rows.
I need to reverse only the order of the columns, while keeping the order of the rows.
So for example:
0,1,2,3,4,5,6
7,8,9,9,10,11,12
has to be
6,5,4,3,2,1,0
12,11,10,9,8,7
Right now, i use a huge IF statement for that:
for (dd *d in dates[i]) {
if (tileNum==0) {
reversedTileNum = 6;
} else if (tileNum==1) {
reversedTileNum = 5;
}else if (tileNum==2) {
reversedTileNum = 4;
}else if (tileNum==3) {
reversedTileNum = 3;
}else if (tileNum==4) {
reversedTileNum = 2;
}else if (tileNum==5) {
reversedTileNum = 1;
} else if (tileNum==6) {
reversedTileNum = 0;
}
....
....
}

Answer 1

Here's a solution that should be easy to drop into any project. It involves two categories: one on NSMutableArray that provides a method to swap objects at two indices, and one on NSArray that provides the -arrayByReversingGroups: method. The idea is to swap the elements in pairs within a group, reversing the group. If number of elements in the array isn't an even multiple of groupSize, the extras at the end are left untouched.
The code presented here is a complete program, so you can see an example of using -arrayByReversingGroups: in the main() function.
#import <Foundation/Foundation.h>
#interface NSArray(Reversible)
-(NSArray*)arrayByReversingGroups:(int)groupSize;
#end
#interface NSMutableArray(Swappable)
-(void)swapObjectAtIndex:(int)first withObjectAtIndex:(int)second;
#end
#implementation NSArray(Reversible)
-(NSArray*)arrayByReversingGroups:(int)groupSize
{
NSMutableArray *newArray = [self mutableCopy];
// Iterate over the array in chunks of groupSize elements. i will be first index in
// the current chunk.
for (int i = 0; (i + groupSize) < [newArray count]; i += groupSize) {
// Iterate over the items in the current chunk, swapping the bth and
// (groupsize-b-1)th elements until they meet at groupsize/2.
for (int b = 0; b <= (groupSize / 2); b++) {
int first = i + b;
int second = i + groupSize - b - 1;
[newArray swapObjectAtIndex:first withObjectAtIndex:second];
}
}
return [newArray copy];
}
#end
#implementation NSMutableArray(Swappable)
-(void)swapObjectAtIndex:(int)first withObjectAtIndex:(int)second
{
id temp = [[self objectAtIndex:second] retain];
[self replaceObjectAtIndex:second withObject:[self objectAtIndex:first]];
[self replaceObjectAtIndex:first withObject:temp];
[temp release];
}
#end
int main (int argc, const char * argv[])
{
#autoreleasepool {
NSArray *array = [NSArray arrayWithObjects:
#"1", #"2", #"3", #"4", #"5", #"6", #"7", #"8", #"9", #"10", #"11", #"12", nil];
NSLog(#"Original: %#", array);
NSLog(#"Reversed: %#", [array arrayByReversingGroups:5]);
}
return 0;
}

Answer 2

I can give you the logic.. you will have to write the code...
First create a function where you pass in an array(here you will send in a row.) then in this function create a new tempeorary array and store all the values for that row in this column then overwrite the original array in reverse order from this new array and return this to the full matrix and store it in there ... hope it helps.