Parsing Every Element of Array Together - iOS

Question

I have an array like following example:

[
    {
        "lx": 144,
        "ly": 57,
        "mx": 144,
        "my": 56
    },
    {
        "lx": 321,
        "ly": -4,
        "mx": 298,
        "my": 16
    }
]

I want to set every element with its half value.

In short, I want something like following.

[
    {
        "lx": 72,
        "ly": 28.5,
        "mx": 72,
        "my": 28
    },
    {
        "lx": 160.5,
        "ly": -2,
        "mx": 149,
        "my": 8
    }
]

I am using following code:

    NSMutableArray * tempArray = [NSMutableArray arrayWithCapacity:0];
    for (int i = 0; i < jsonArray.count; i++)
    {
        NSMutableDictionary * tempDict = [NSMutableDictionary dictionaryWithDictionary:(NSDictionary *)jsonArray[i]];
        tempDict[@"lx"] = @([tempDict[@"lx"] intValue]/2);
        tempDict[@"ly"] = @([tempDict[@"ly"] intValue]/2);
        tempDict[@"mx"] = @([tempDict[@"mx"] intValue]/2);
        tempDict[@"my"] = @([tempDict[@"my"] intValue]/2);
        [tempArray addObject:tempDict];
    }

I have done it with a loop and it is working fine with small amount of data.

But when I have large data, App behaviour becomes slow.

Any help will be appreciated

Thanks...

If you want to improve its performance, you'd better post your code. — KudoCC
– KudoCC, Commented Aug 8, 2014 at 8:18
I wonder if "9/2=4" is ok ? I mean you won't get float result in your code. — KudoCC
– KudoCC, Commented Aug 8, 2014 at 8:25
@KudoCC, It a minor thing. but focus on the overall question.. — Akshit Zaveri
– Akshit Zaveri, Commented Aug 8, 2014 at 8:33

Mattias · Accepted Answer · 2014-08-08 07:33:05Z

1

Perhaps you could compute it asynchronous in a background thread so that you don't block the UI.

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
    // Code to execute in background thread
});

answered Aug 8, 2014 at 7:33

Mattias

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Comments

KudoCC · Accepted Answer · 2014-08-08 08:44:16Z

1

In your code, I find you don't take float result into account, so I can use shift operator instead of dividing.

// allocate enough memory
NSMutableArray * tempArray = [NSMutableArray arrayWithCapacity:[jsonArray count]];
// fast enumerate
for (NSDictionary *dict in jsonArray) {
    NSMutableDictionary * tempDict = [NSMutableDictionary dictionaryWithDictionary:dict];
    // use shift operator instead of dividing by 2
    tempDict[@"lx"] = @([tempDict[@"lx"] intValue]>>1);
    tempDict[@"ly"] = @([tempDict[@"ly"] intValue]>>1);
    tempDict[@"mx"] = @([tempDict[@"mx"] intValue]>>1);
    tempDict[@"my"] = @([tempDict[@"my"] intValue]>>1);
    [tempArray addObject:tempDict];
}

I don't think this method will improve much performance because we must enumerate all the items, the time complexity is not changed.

edited Aug 8, 2014 at 8:44

answered Aug 8, 2014 at 8:36

KudoCC

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2 Comments

Nirav Gadhiya Over a year ago

Thanks.... +1 for your effort and good solution. But i am looking for more optimised code. Trying with setValue:ForKeyPath: now...

KudoCC Over a year ago

@NJGadhiya You can have a try but I think it does the same thing.

Pawan Rai · Accepted Answer · 2014-08-08 08:45:01Z

-1

Addressing your comment to another answer: I want to slow down the process of parsing the data:

If you want to return control to the main thread to allow other actions to happen you can use

[[NSRunLoop mainRunLoop] runUntilDate:[NSDate date]];

which will temporarily pause your current data processing loop and allow other things to happen. Obviously you can also change [NSDate date] to a date further in the future if you want to slow down more.

edited Aug 8, 2014 at 8:45

Pawan Rai

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answered Aug 8, 2014 at 7:42

CharlesA

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2 Comments

cacau Over a year ago

Not a great idea - using one of the mechanisms in IOS to perform work in the background should be preferred than mucking around with the runloop

CharlesA Over a year ago

@cacau, the OP said in the comment to the previous answer "I want to slow down the process of parsing the data". The code above should do that.

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