Faster way to iterate through a large NSArray of dictionaries

Question

I created a "invite friends" feature for a iOS app I'm building. I was able to add alphabetical sections A-Z, by iterating through the large array, using NSPredicate picking out all names that start with A then B all the way to Z. Saving them into a dictionary were the keys are A-Z.

Everything works, but opening that view takes about 7 seconds from the moment I click the "invite friends" button.

What can I do to make this load seamlessly or atleast make it seem seamless to the users and improving the design and my code?

Here is my code

-(void)testing {

NSMutableArray *stringName = [[NSMutableArray alloc] init];

for (NSDictionary* item in self.tableData) {

   // self.user = item;
    NSString* firstName = [item objectForKey:@"firstName"];
    [stringName addObject:firstName];


    NSPredicate *aPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'A'"];
    NSArray *beginWithA = [stringName filteredArrayUsingPredicate:aPredicate];

    NSPredicate *bPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'B'"];
    NSArray *beginWithB = [stringName filteredArrayUsingPredicate:bPredicate];

    NSPredicate *cPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'C'"];
    NSArray *beginWithC = [stringName filteredArrayUsingPredicate:cPredicate];

    NSPredicate *dPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'D'"];
    NSArray *beginWithD = [stringName filteredArrayUsingPredicate:dPredicate];

    NSPredicate *ePredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'E'"];
    NSArray *beginWithE = [stringName filteredArrayUsingPredicate:ePredicate];

    NSPredicate *fPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'F'"];
    NSArray *beginWithF = [stringName filteredArrayUsingPredicate:fPredicate];

    NSPredicate *gPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'G'"];
    NSArray *beginWithG = [stringName filteredArrayUsingPredicate:gPredicate];

    NSPredicate *hPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'H'"];
    NSArray *beginWithH = [stringName filteredArrayUsingPredicate:hPredicate];

    NSPredicate *iPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'I'"];
    NSArray *beginWithI = [stringName filteredArrayUsingPredicate:iPredicate];

    NSPredicate *jPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'J'"];
    NSArray *beginWithJ = [stringName filteredArrayUsingPredicate:jPredicate];

    NSPredicate *kPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'K'"];
    NSArray *beginWithK = [stringName filteredArrayUsingPredicate:kPredicate];

    NSPredicate *lPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'L'"];
    NSArray *beginWithL = [stringName filteredArrayUsingPredicate:lPredicate];

    NSPredicate *mPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'M'"];
    NSArray *beginWithM = [stringName filteredArrayUsingPredicate:mPredicate];

    NSPredicate *nPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'N'"];
    NSArray *beginWithN = [stringName filteredArrayUsingPredicate:nPredicate];

    NSPredicate *oPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'O'"];
    NSArray *beginWithO = [stringName filteredArrayUsingPredicate:oPredicate];

    NSPredicate *pPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'P'"];
    NSArray *beginWithP = [stringName filteredArrayUsingPredicate:pPredicate];

    NSPredicate *qPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'Q'"];
    NSArray *beginWithQ = [stringName filteredArrayUsingPredicate:qPredicate];

    NSPredicate *rPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'R'"];
    NSArray *beginWithR = [stringName filteredArrayUsingPredicate:rPredicate];

    NSPredicate *sPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'S'"];
    NSArray *beginWithS = [stringName filteredArrayUsingPredicate:sPredicate];

    NSPredicate *tPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'T'"];
    NSArray *beginWithT = [stringName filteredArrayUsingPredicate:tPredicate];

    NSPredicate *uPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'U'"];
    NSArray *beginWithU = [stringName filteredArrayUsingPredicate:uPredicate];

    NSPredicate *vPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'V'"];
    NSArray *beginWithV = [stringName filteredArrayUsingPredicate:vPredicate];

    NSPredicate *wPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'W'"];
    NSArray *beginWithW = [stringName filteredArrayUsingPredicate:wPredicate];

    NSPredicate *xPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'X'"];
    NSArray *beginWithX = [stringName filteredArrayUsingPredicate:xPredicate];

    NSPredicate *yPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'Y'"];
    NSArray *beginWithY = [stringName filteredArrayUsingPredicate:yPredicate];

    NSPredicate *zPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'Z'"];
    NSArray *beginWithZ = [stringName filteredArrayUsingPredicate:zPredicate];







    // Dictionary
    self.sectionDict = [[NSMutableDictionary alloc] init];

    if (![beginWithA count] == 0) {
        _sectionDict[@"A"] = beginWithA;
    }
    if (![beginWithB count] == 0) {
        _sectionDict[@"B"] = beginWithB;
    }
    if (![beginWithC count] == 0) {
        _sectionDict[@"C"] = beginWithC;
    }
    if (![beginWithD count] == 0) {
        _sectionDict[@"D"] = beginWithD;
    }
    if (![beginWithE count] == 0) {
        _sectionDict[@"E"] = beginWithE;
    }
    if (![beginWithF count] == 0) {
        _sectionDict[@"F"] = beginWithF;
    }
    if (![beginWithG count] == 0) {
        _sectionDict[@"G"] = beginWithG;
    }
    if (![beginWithH count] == 0) {
        _sectionDict[@"H"] = beginWithH;
    }
    if (![beginWithI count] == 0) {
        _sectionDict[@"I"] = beginWithI;
    }
    if (![beginWithJ count] == 0) {
        _sectionDict[@"J"] = beginWithJ;
    }
    if (![beginWithK count] == 0) {
        _sectionDict[@"K"] = beginWithK;
    }
    if (![beginWithL count] == 0) {
        _sectionDict[@"L"] = beginWithL;
    }
    if (![beginWithM count] == 0) {
        _sectionDict[@"M"] = beginWithM;
    }

    //
    if (![beginWithN count] == 0) {
        _sectionDict[@"N"] = beginWithN;
    }
    if (![beginWithO count] == 0) {
        _sectionDict[@"O"] = beginWithO;
    }
    if (![beginWithP count] == 0) {
        _sectionDict[@"P"] = beginWithP;
    }
    if (![beginWithQ count] == 0) {
        _sectionDict[@"Q"] = beginWithQ;
    }
    if (![beginWithR count] == 0) {
        _sectionDict[@"R"] = beginWithR;
    }
    if (![beginWithS count] == 0) {
        _sectionDict[@"S"] = beginWithS;
    }
    if (![beginWithT count] == 0) {
        _sectionDict[@"T"] = beginWithT;
    }
    if (![beginWithU count] == 0) {
        _sectionDict[@"U"] = beginWithU;
    }
    if (![beginWithV count] == 0) {
        _sectionDict[@"V"] = beginWithV;
    }
    if (![beginWithW count] == 0) {
        _sectionDict[@"W"] = beginWithW;
    }
    if (![beginWithX count] == 0) {
        _sectionDict[@"X"] = beginWithX;
    }
    if (![beginWithY count] == 0) {
        _sectionDict[@"Y"] = beginWithY;
    }
    if (![beginWithZ count] == 0) {
        _sectionDict[@"Z"] = beginWithZ;
    }


}

    self.dictSectionTitles = [[self.sectionDict allKeys] sortedArrayUsingSelector:@selector(localizedCaseInsensitiveCompare:)];


}

Here is the other in which I call the method.

-(void)viewWillAppear:(BOOL)animated {

     [self loadData];

}

- (void)loadData
{
[self.contactsManager importContacts:^(NSArray *contacts)
 {
     self.tableData = contacts;
      [self testing];
     [self.tableView reloadData];
     NSLog(@"contacts: %@",contacts);
 }];

}

Thanks!

to clear your code, just create alphabet array, and then iterate through it http://stackoverflow.com/questions/4377956/is-there-an-easy-way-to-programatically-get-the-alphabet — Vasyl Khmil, Jan 16 '16 at 21:18
FYI - You need to deal with names that don't start with the letter A-Z. What about names using accented letters or names written in other alphabets? — rmaddy, Jan 16 '16 at 21:26
How would I be able to handle that @rmaddy. Can you provide an example or a link to a guide ? Thanks. — Alex Knows, Jan 16 '16 at 21:58

score 2 · Accepted Answer · answered Jan 16 '16 at 21:23

You are essentially traversing the entire array 26 times. You need an algorithm that only traverses once, building up your dictionary as you go along.

NSMutableDictionary *sectionDict = [NSMutableDictionary dictionary];

for (NSString *s in array) {
    NSString *firstLetter = [s substringToIndex:1];

    NSMutableArray *section = sectionDict[firstLetter];
    if (section == nil) {
        section = [NSMutableArray array];
        sectionDict[firstLetter] = section;
    }

    section addObject:s];
}

Faster way to iterate through a large NSArray of dictionaries

1 Answers1