How to turn NSString to a number

Question

I need to sort a list of files according to the number after "_" :

"filename_1" "filename_2" ......

I know that I can extract the number, then sort the filename with the number, but I have to consider what if some illegal name exist and the program turn to be long.

What I want to do is just simply compare the whole String, the same char must has the same number. But when I do [@"word" intValue], the result is zero if the String is not a number. I want to know is there a good way to turn a String into a number.

I recommend renaming this question to "How to sort file names numerically?" because you're doing more than converting an NSString to a number. — Kevin Grant, Jun 28 '12 at 05:45

score 2 · Answer 1 · answered Jun 28 '12 at 05:32

2

Take a look at NSString's method:

- (NSComparisonResult)compare:(NSString *)aString options:(NSStringCompareOptions)mask

and the NSNumericSearch option.

answered Jun 28 '12 at 05:32

Julien

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score 1 · Answer 2 · edited May 23 '17 at 12:27

If you wish to sort them on your own then you will need to use the

- (NSComparisonResult)compare:(NSString *)aString;

routine.

Here is the reference to the NSComparisonResult capable outputs.

These constants are used to indicate how items in a request are ordered.

enum {
    NSOrderedAscending = -1,
    NSOrderedSame,
    NSOrderedDescending
};
typedef NSInteger NSComparisonResult;

Constants: NSOrderedAscending The left operand is smaller than the right operand.

NSOrderedSame The two operands are equal.

NSOrderedDescending The left operand is greater than the right operand.

If you think it easier, your can fill an NSArray with your separated strings, then use something like the following:

sortedArray = [anArray sortedArrayUsingSelector:@selector(localizedCaseInsensitiveCompare:)];

Link to a good QA from SO:

How to sort a NSArray alphabetically?

There is 1 final way I can think of in your case. That would be to use the hasPrefix method of NSString to make sure that each of your strings begins with "filename_" as a first validation. afterwards substring the overall string just getting the remaining string after the "filename_". If all of your filenames are to have a number of 1 or greater, then a 0 means the string is invalid at this point, else the intValue should return a valid positive integer, and you can sort via the integer values.

score 0 · Answer 3 · answered Jun 28 '12 at 05:34

This should work:

NSString *good = @"filename_1";
NSString *bad = @"filename";

NSCharacterSet *letterSet= [NSCharacterSet letterCharacterSet];

good = [good stringyByTrimmingCharactersInSet:letterSet]; // 1
bad = [bad stringByTrimmingCharactersInSet:letterSet]; // <empty>

score 0 · Answer 4 · answered Jun 28 '12 at 05:35

You can use following coe to sort the array containing the list of File Objects:

NSSortDescriptor *aSortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"fileName" ascending:YES];
[arrayOfFileNames sortUsingDescriptors:[NSArray arrayWithObject:aSortDescriptor]];

Hope this is helpful to you...

score 0 · Answer 5 · answered Jun 28 '12 at 05:40

I think you can not compare it with NSString because NSString follows 1,10,11,12,13,14 .....2,20,21,22 ......this type of ascending order while integer follows like 0,1,2,3,4,5,6,7....... and so on..... So you have to split the last character from string then will have to compare.

well how to short string in ascending order ....

NSMutableArray *array = [NSMutableArray arrayWithObjects:@"f_1",@"f_2",@"f_12",@"f_6",@"f_9",@"f_4", nil];
 NSSortDescriptor *name = [[[NSSortDescriptor alloc] initWithKey:@"" ascending:YES] init];
[array sortUsingDescriptors:[NSMutableArray arrayWithObjects:name, nil]];

but this will give you string shorting not according to number.

Thank You!

How to turn NSString to a number

5 Answers5