Extracting specific data from a Mutable Dictionary - iphone

Question

I have a Mutable Dictionary which allows people to choose a selection of days of the week. Once a day has been selected the state is updated using numberWithBool.
When I NSLog the output it looks something like this:
{
day = Monday;
isSelected = 1;
},
{
day = Tuesday;
isSelected = 0;
},
{
day = Wednesday;
isSelected = 0;
},
{
day = Thursday;
isSelected = 0;
},
{
day = Friday;
isSelected = 0;
},
{
day = Saturday;
isSelected = 0;
},
{
day = Sunday;
isSelected = 1;
}
I would like to be able to extract the chosen days and produce the output in the form of a string. So in this example the output would be: Monday, Sunday
How can I do this?
My code for creating the dictionary is below:
NSMutableArray * tempSource = [[NSMutableArray alloc] init];
NSArray *daysOfWeek = [NSArray arrayWithObjects:#"Monday", #"Tuesday", #"Wednesday", #"Thursday", #"Friday", #"Saturday", #"Sunday",nil];
for (int i = 0; i < 7; i++)
{
NSString *dayOfWeek = [daysOfWeek objectAtIndex:i];
NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithObjectsAndKeys:dayOfWeek, #"day", [NSNumber numberWithBool:NO], #"isSelected",nil];
[tempSource addObject:dict];
}
[self setSourceArray:tempSource];
[tempSource release];

Answer 1

You can loop thru all of your items in the array and build a side-array only containing names of the day (1), or you can use a predicate and then KVC to extract the days directly (2).
Then join the components of the filtered array into a string.
Solution 1:
NSMutableArray selectedDays = [[NSMutableArray alloc] init];
for(NSDictionary* entry in sourceArray)
{
if (([entry objectForKey:#"isSelected"] boolValue]) {
[selectedDays addObject:[entry objectForKey:#"day"]];
}
}
NSString days = [selectedDays componentsJoinedByString:#", "];
[selectedDays release];
Solution 2:
NSPredicate* filter = [NSPredicate predicateWithFormat:#"SELF.isSelected == 1"]; // not sure about the exact format (no mac here to test right now so you may adapt a bit if it does not work directly)
// get the array of dictionaries but only the ones that have isSelected==1
NSArray selectedEntries = [sourceArray filteredArrayUsingPredicate:filter];
NSArray selectedDays = [selectedEntries valueForKey:#"day"]; // extract the "days" keys of the dictionaries. We have a NSArray of strings then.
NSString days = [selectedDays componentsJoinedByString:#", "];
As a side note, your way of doing this is quite strange. Why having an NSArray of NSDictionaries for this? As this is simple and a static-size array containing only BOOL, you may instead for this particular case simply use C array BOOL selected[7] and nothing more.
Then to have the name of the weekdays you should instead use the methods of NSCalendar/NSDateFormatter/NSDateComponents to get the standard names of the weekdays (automatically in the right language/locale of the user): create an NSDate using a NSDateComponent for which you simply define the weekday component, then use an NSDateFormatter to convert this to a string, choosing a string format that only display the weekday name.
-(void)tableView:(UITableView*)tv didSelectRowAtIndexPath:(NSIndexPath*)indexPath {
// selectedDays is an instance variable in .h declared as
// BOOL selectedDays[7];
selectedDays[indexPath.row] = ! selectedDays[indexPath.row];
[tv reloadData];
}
-(UITableViewCell*)tableView:(UITableView*)tv cellForRowAtIndexPath:(NSIndexPath*)indexPath {
static NSString* kCellIdentifier = #"DayCell";
UITableViewCell* cell = [tv dequeueReusableCellWithIdentifier:kCellIdentifier];
if (!cell) {
cell = [[[UITableViewCell alloc] initWithStyle:... identifier:kCellIdentifier]; autorelease];
// configure here every property that is common to all for your cells (text color, etc)
}
// configure here things that will change from cell to cell
cell.accessoryType = selectedDays[indexPath.row] ? UITableViewCellAccessoryTypeCheckmarck : UITableViewCellAccessoryTypeNone;
cell.textLabel.text = weekdayName(indexPath.row);
return cell;
}
// Simple C function to return the name of a given weekday
NSString* weekdayName(int weekday)
{
#if WAY_1
/**** Solution 1 ****/
// Optimization note: You may compute this once for all instead of recomputing it each time
NSDateComponents* comp = [[[NSDateComponents alloc] init] autorelease];
[comp setWeekday:weekday+1]; // weekdays start at 1 for NSDateComponents
NSDate* d = [[NSCalendar currentCalendar] dateFromComponents:comp];
NSDateFormatter* df = [[[NSDateFormatter alloc] init] autorelease];
[df setDateFormat:#"EEEE"]; // format for the weekday
return [[df stringFromDate:d] capitalizedString];
#else
/**** Solution 2 ****/
NSDateFormatter* df = [[[NSDateFormatter alloc] init] autorelease];
NSArray* weekdayNames = [df weekdaySymbols]; // or maybe one of its sibling methods? check what is returned here to be sure
return [weekdayNames objectAtIndex:weekday];
#endif
}

Answer 2

Is there a reason that you avoid NSMutableIndexSet?
It may simplify your code to:
NSArray *daysOfWeek = ...;
NSMutableIndexSet *indexesOfSelectedDays = ...;
NSArray *selectedDays = [daysOfWeek objectsAtIndexes:indexesOfSelectedDays];

Answer 3

Use NSPredicate to create a predicate that selects the items in the array where isSelected is true, and use that to filter the array using NSArray's -filteredArrayUsingPredicate: method. (#Miraaj posted a good example of using a predicate faster than I could type it.) Then take that filtered array and pick out the days, like this:
NSArray *selectedItems = [sourceArray filteredArrayUsingPredicate:somePredicate];
NSArray *days = [selectedItems valueForKey:#"day"];
NSString *daysString = [days componentsJoinedByString#", "];