Sum an Array - Objective-C

Question

I'm just starting out and I'm looking for an easy way to sum a simple array. I've read into apple developer site on key value coding and I don't understand how to apply that to my array or if that's the appropriate way to sum this.

My stumbling block with the key value coding is the .keypathToProperty - I can sort of understand that you need a further reference in a 2D array but they don't show the array code, only the keypath to the title of the row so I can't figure it out yet.

NSMutableArray *numArray = [NSMutableArray arrayWithCapacity:4];
    [numArray addObject:num1];
    [numArray addObject:num2];  
    [numArray addObject:num3];
    [numArray addObject:num4];

I appreciate the replies!

Thanks

Graham

Dave DeLong · Accepted Answer · 2011-01-10 04:55:24Z

79

The automatic way to do it is:

NSNumber * sum = [numArray valueForKeyPath:@"@sum.self"];

But if you're just starting out, I would recommend avoiding the collection key-path operators and go for the more simple way:

double sum = 0;
for (NSNumber * n in numArray) {
  sum += [n doubleValue];
}

answered Jan 10, 2011 at 4:55

Dave DeLong

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2 Comments

Jacob Relkin Over a year ago

Jeez, I did not know about @sum.self, wow, every day I am reminded of how much I don't know.

Ankit Over a year ago

Interestingly there are such key also like "max.self", "min.self"... Awesome solution..

Community · Accepted Answer · 2017-05-23 11:47:15Z

2

Swift 3: (Dave DeLong's method transformed):

let sum = (numArray as AnyObject).value(forKeyPath:"@sum.self") as! Double

This should work in a similar fashion to it's Objective-C counterpart.

edited May 23, 2017 at 11:47

CommunityBot

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answered Jan 27, 2017 at 9:27

l'L'l

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2 Comments

Mike Sprague Over a year ago

I know you're doing it as an example of using keypaths, but for any newer Swift readers, you might want to use a reduce instead! let sum = numArray.reduce(0) { $0 + $1 }

l'L'l Over a year ago

@MikeSprague: I'm not disagreeing with you on which might be more appropriate, although I'm interested in your reasoning why an alternative method shouldn't be presented. The reason I like this method is that for the amount of code involved it works quite well for an array which contains mixed integers and string values.

Massimiliano Kraus · Accepted Answer · 2017-10-13 13:15:20Z

-1

In Swift 4:

let array = [1,2,3,5]
let sum = array.reduce(0, {$0 + $1})
print(sum)

edited Oct 13, 2017 at 13:15

Massimiliano Kraus

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answered Oct 13, 2017 at 7:52

garg

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1 Comment

Silis Alin Over a year ago

This is an Objective-C question.

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