Question

I have this piece of code for placing elements from an array into the appropriate section in a UITableView depending on their starting letter:

//For each product in the appDelgates products
for (Product *product in appDelegate.m_Products){
    if ([product.category isEqualToString:productType]){

        //firstLetter is equal to the first letter of the products name
        NSString * l_FirstLetter = [product.name substringToIndex:1];
        //convert firstString to uppercase
        l_FirstLetter = [l_FirstLetter uppercaseString];

        //Check what letter firstString is equal to in the alphabet
        //Place in appropriate section
        //If none, place in "Other" category
        if ([l_FirstLetter isEqualToString:@"A"]) {
            [[m_AlphabetDictionary objectAtIndex:0] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"B"]) {
            [[m_AlphabetDictionary objectAtIndex:1] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"C"]) {
            [[m_AlphabetDictionary objectAtIndex:2] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"D"]) {
            [[m_AlphabetDictionary objectAtIndex:3] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"E"]) {
            [[m_AlphabetDictionary objectAtIndex:4] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"F"]) {
            [[m_AlphabetDictionary objectAtIndex:5] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"G"]) {
            [[m_AlphabetDictionary objectAtIndex:6] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"H"]) {
            [[m_AlphabetDictionary objectAtIndex:7] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"I"]) {
            [[m_AlphabetDictionary objectAtIndex:8] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"J"]) {
            [[m_AlphabetDictionary objectAtIndex:9] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"K"]) {
            [[m_AlphabetDictionary objectAtIndex:10] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"L"]) {
            [[m_AlphabetDictionary objectAtIndex:11] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"M"]) {
            [[m_AlphabetDictionary objectAtIndex:12] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"N"]) {
            [[m_AlphabetDictionary objectAtIndex:13] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"O"]) {
            [[m_AlphabetDictionary objectAtIndex:14] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"P"]) {
            [[m_AlphabetDictionary objectAtIndex:15] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"Q"]) {
            [[m_AlphabetDictionary objectAtIndex:16] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"R"]) {
            [[m_AlphabetDictionary objectAtIndex:17] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"S"]) {
            [[m_AlphabetDictionary objectAtIndex:18] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"T"]) {
            [[m_AlphabetDictionary objectAtIndex:19] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"U"]) {
            [[m_AlphabetDictionary objectAtIndex:20] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"V"]) {
            [[m_AlphabetDictionary objectAtIndex:21] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"W"]) {
            [[m_AlphabetDictionary objectAtIndex:22] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"X"]) {
            [[m_AlphabetDictionary objectAtIndex:23] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"Y"]) {
            [[m_AlphabetDictionary objectAtIndex:24] addObject:product];
        }
        else if ([l_FirstLetter isEqualToString:@"Z"]) {
            [[m_AlphabetDictionary objectAtIndex:25] addObject:product];
        }
        else {
            [[m_AlphabetDictionary objectAtIndex:26] addObject:product];
        }

    }
}

Is there a better approach?

Thanks,

Jack

Answer 1

transform the char to an int minus the int of a char of a “A”

and just use [[m_AlphabetDictionary objectAtIndex:myInt] addObject:product];

and make sure, you are only using letters. and If you want to support small and big letters, you have to subtract char of ‘a’ from small letters.

there are more sophisticated approaches if you need to support locales and diacritics in the future, but this will work for the a…z and A…Z sets defined in the OP:

First, the wordy version which documents how this works:

static inline NSUInteger InsertionIndexForProductNamed(NSString * product) {
  assert(0 < product.length && "invalid argument");

  const int A = 'A';
  const int Z = 'Z';
  const int a = 'a';
  const int z = 'z';

  const unichar first = [product characterAtIndex:0];
  const bool isLowercaseAZ = a <= first && z >= first;
  const int uppercase = isLowercaseAZ ? (first + A - a) : first;
  const bool isUppercaseAZ = A <= uppercase && Z >= uppercase;

  if (isUppercaseAZ) {
    const int result = uppercase - A;
    return (NSUInteger)result;
  }
  else {
    /* not A-Z. place in 'other' */
    return 26;
  }
}

Now the short version, which is more along the lines of what you may see in the wild:

static inline NSUInteger InsertionIndexForProductNamed(NSString* product) {
  assert(0 < product.length && "invalid argument");

  const unichar first = [product characterAtIndex:0];
  switch (first) {
    case 'A'...'Z' :
      return first - 'A';
    case 'a'...'z' :
      return first - 'a';
    default :
      return 26;
  }
}

In use:

/* For each product in the appDelgates products */
for (Product * product in appDelegate.m_Products) {
  if ([product.category isEqualToString:productType]) {
    const NSUInteger idx = InsertionIndexForProductNamed(product.name);
    [[m_AlphabetDictionary objectAtIndex:idx] addObject:product];
  }
}

Finally, the short in-line implementation could take this form:

/* For each product in the appDelgates products */
for (Product * product in appDelegate.m_Products) {
  if ([product.category isEqualToString:productType]) {
    const NSUInteger insertionIndex;
    const unichar first = [product characterAtIndex:0];
    switch (first) {
      case 'A'...'Z' :
        insertionIndex = first - 'A';
        break;
      case 'a'...'z' :
        insertionIndex = first - 'a';
        break;
      default :
        insertionIndex = 26; // 26 is the index of the 'other' category
        break;
    }
    [[m_AlphabetDictionary objectAtIndex:insertionIndex] addObject:product];
  }
}

_{please also note my ObjC/Block-style answer}