sorting NSMutableArray contain NSArray using sortedArrayUsingComparator

Question

I got problem for sorting array of nsdate. so i have array of date inside nsmutablearray

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"yyyy-MM-dd"];
NSArray *arrString = [[NSArray alloc] initWithObjects:@"2012-05-01", @"2012-02-01", @"2012-22-03", @"2012-05-01", @"2012-15-01", nil];
NSMutableArray *arrDate = [[NSMutableArray alloc] initWithCapacity:arrString.count];
for (NSString *item in arrString) {
    NSDate *date = [dateFormatter dateFromString:item];
    [arrDate addObject:date];
}

as i saw in many cases they use code like this to sort array:

NSArray *sortedArray = [arrDate sortedArrayUsingComparator:^(id firstObject, id secondObject) {
    return [((NSDate *)firstObject) compare:((NSDate *)secondObject)];
}];

i tried to put my array on it, but not worked. Anyone can help me how actully best way to sort nsmutablearray contain nsdate. I want to put the latest date at top of the index array.

So the real question is, how can i sort data inside arrDate?

Thank you.

"i tried to put my array on it, but not worked." What didn't work? Was the array empty? Did it crash from trying to insert a nil date? Did the array just not sort? Because the obvious thing I can see is that your date format does not match the dates in the array. Remove the hh:mm:ss since the strings contain no time information. — Joe
– Joe, Commented May 9, 2012 at 14:50
dont worry the format just fine, it just typo when i post it. Now it fixed. My problem is how i can sort the date inside the array. The sorting didnt work, how can i use sortedArrayUsingComparator for my nsmutablearray? — dejoong
– dejoong, Commented May 9, 2012 at 15:51

JeremyP · Accepted Answer · 2012-05-09 16:34:44Z

1

Your date format does not match the date strings you are using.

yyyy-MM-dd hh:mm:ss

means the dates you supply should look something like:

2012-05-09 15:54:21
        ^^ Day
     ^^ Month

i.e. your strings are missing the hours, minutes and seconds and you have some dates with month 22 and month 15. If a date formatter can't parse a date, I think it returns nil which would mean you are trying to put nil into an array, which will cause an exception.

Edit

To actually sort the dates, your sample code looks OK except that you want most recent first, so reverse the compare:

NSArray *sortedArray = [arrDate sortedArrayUsingComparator:^(id firstObject, id secondObject) {
     return [secondObject compare: firstObject];
}];

Or with a mutable array, you can sort in place:

[arrDate sortUsingComparator:^(id firstObject, id secondObject) {
     return [secondObject compare: firstObject];
}];

edited May 9, 2012 at 16:34

answered May 9, 2012 at 14:56

JeremyP

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3 Comments

dejoong Over a year ago

sorry the format doesnt matter, it just typo when i posted the question, i've fixed my code. So we can back to the original question how can i sort the array contain nsdate?

dejoong Over a year ago

Hi Jeremy, i think it works with your method, thank you. But i curious why this string -> @"2012-05-08 19:00:43" not works with NSDateFormatter @"yyyy-MM-dd hh:mm:ss" if i using [dateFormatter dateFromString:@"2012-05-08 19:00:43"]; the return is nil. do u know why?

dejoong Over a year ago

ahh i got it.., the format should be @"yyyy-MM-dd HH:mm:ss" instead of @"yyyy-MM-dd hh:mm:ss" . tx anyway

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