I've been working on a search algorithm all afternoon and I'd like some opinions. Some of what I'm doing is specific to iOS, but the general concepts are not.
I'm trying to display a set of data, a directory. In the directory I have departments and people. I know this sounds like a textbook example, hear me out. It's not homework, I promise. (I can provide screenshots of what I'm working on.)
I have an array of entries, where there are those two kinds of directory entries. I need to sort the entries by name, then break up the array into smaller arrays, where each sub-array contains the entries that begin with the same letter.
Additionally, I need to account for a search string that the user may enter.
My general process is this:
Filter all the entries that match the type and search string if there is one. For this step I use an NSPredicate:
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"type == %i AND searchableContents B[cd] %#", type, searchString];
if (!searchString || searchString.length == 0)
{
predicate = [NSPredicate predicateWithFormat:#"type == %i", type];
}
NSArray *array = [_directoryContents filteredArrayUsingPredicate:predicate];
Sort the results alphabetically.
array = [array sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
return [((BRKDirectoryEntry *)obj1).comperableTitle compare:((BRKDirectoryEntry *)obj2).comperableTitle];
}];
Break up the results into smaller arrays. For performance, I skip this step if we're searching, but it doesn't seem to help.
if(alphabetized)
{
array = [self _alphabetizedArrayFromPresortedArray:array];
}
The performance of this on a total of 950 entries is abysmal.
Now, for my default display, I can get away with simply caching the sorted data in memory, and then display and scrolling performs nicely, but for search-as-I-type, there's simply no way to achieve the smooth performance that users expect.
Any pointers or tips?
Yes. Forget files and keep it in a database. Create your indexes Everything becomes a simple SQL statement.
Related
I have an API, from which I load Shop objects.
Shop object has NSString *assortment field, containing products you can buy in shop, in my syntax it's eg. "water,milk,potatoes,bread,ketchup".
NSString *assortment = #"water, milk, potatoes, bread, ketchup";
I load shops from my local database to an NSArray *shops.
NSArray *shops = [Shop MR_findAll];
I want to find all objects in my shops array (using MR_findByAttribute maybe?) that contain word "bread" in their assortment field.
I know I can split my string and check for every single assortment position - but that sounds not intuitive to me. I feel like there's better solution, maybe:
NSArray *shopsWithBread = [Shop MR_findByAttribute:#"assortment" withValue:#"<bread regex?>"];
Do you know any nice way to do it? Do you have maybe another good idea how to find all those shops? Maybe you're sure it can't be done this way and I have to write search engine myself?
Thank you in advance for all answers.
Karol
Ok, I've found the solution - I'm using predicate.
NSPredicate *breadSearchPredicate = [NSPredicate predicateWithFormat:#"assortment contains[cd] %#", #"bread"];
NSArray *shopsWithBread = [Shop MR_findAllWithPredicate:breadSearchPredicate];
assortment is my field name; contains[cd] is a kind of instruction, checking for containing a string give - here #"bread".
NSPredicate - nicely explained here: http://nshipster.com/nspredicate/
Im trying to implement something that I'm sure have been implemented a million times before, a search in the core data database, displayed in a table using a fetchRequestController and the searchController.
My problem is writing the NSPredicate for the NSFetchRequest. According to the NSPredicate guide by Apple, not everything you can do in Sqlite is possible with core data.
I have been trying to find a solution for some time, but maybe one of you can use his experience to help me.
CoreData DB description:
Shops has a MANY TO MANY relationship with DiscountProgam.
My use case is as follows: I need to filter out Shops who's name/address/zip/city contains the search string. that's the easy part.
The hard part is creating the section of the database I want to filter from, because I have an array of "active" discountPrograms UID's, and I only want shops that have one of the active discount programs in their "discountPrograms" set. So in pseudo code that would be:
FROM Shops who have at least one discountProgram who's uid IN activeDiscountProgramsArray WHERE name/address/zip/city CONTAINS searchString
Is this possible? am I over reaching the limits of predicates?
If so, how could I do it differently?
Yes, NSPredicate can analyse both the direct attributes of the target entity of a fetch and the attributes of its relationships. Try:
NSArray *validUIDs = ...;
NSString *searchTerm = ...;
[NSPredicate predicateWithFormat:#"(name CONTAINS[cd] %# OR zip CONTAINS[cd] %#) AND (SUBQUERY(discountProgram, $d, $d.UID IN %#).#count > 0)", searchTerm, searchTerm, validUIDs];
I'm working on an app where I have two entities, Post <-->> StreamType. When I create posts I assign StreamType:s like this:
// streamType == one of my default streamTypes
[post addStreamTypesObject:streamType];
My predicate for finding posts that have a certain StreamType looks like this:
predicate = [NSPredicate predicateWithFormat:#"ANY streamTypes.type = %#", [NSNumber numberWithInt:self.pageType]];
I'm not sure why this happens. Any ideas?
Edit
What I basically want is to fetch all Posts that have the right StreamType. Seemed after all that my fetchrequest only returns 1 item from the database. So probably nothing wrong with my tableview.
Edit 3
The problem was with my relationship, should be many-to-many, not one to many. Therefore it only returned one Post item.
First: test if the other code is ok. Simply, remove the predicate (comment the setPredicate line). You should see ALL objects in your tableview.
Right?
Second: check if self.pageType is set correctly. I don't see in your code how you set self.pageType
Test your predicate, add an NSLog like this and check if the result is ok:
NSLog(#"ANY streamTypes.type = %d", self.pageType);
Third:
As far as I understand, you have this situation:
One Post has only one stream type
One stream type has multiple posts.
The ANY keyword is used in situations where you want, for example, obtain all stream types where a particular condition is satisfied at least one time. for example (assuming you have a "content" instance variable on your post, containing the text of the post)
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"ANY post.content CONTAINS[cd] %#", #"aWord"];
In this case, you will obtain all stream types in which there are posts containing "aWord" particular word in the text.
Your case is simpler. I think that you should simply use:
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"streamTypes.type = %d", self.pageType];
Try and let me know
I was just having the same issue using Core Data with Swift and just wanted to add this answer in incase anybody else is having a similar issue.
This was my NSPredicate code:
let predicate = NSPredicate(format: "routine == %#", self.selectedRoutine)
Routine holds multiple exercise objects which I was trying to return. An exercise can only have one routine but a routine can have many exercises.
Turns out I'd forgotten to select 'To Many' as the relationship type for the exercises relationship in my routine entity using the Data Model inspector. It was set as 'To One'.
I have an array of data that is displayed in a table. The array has multiple fields, including two specific ones I want to filter, the "call type" and the "county". The value for "call type" is either an "f" or "e" and the value for the county is either "w" or "c". I want to have 4 UISwitch's to to either turn on/off the "w", turn on/off the "c" etc. Its hard to explain but if you go to this website and look at the top right corner, its exactly what I want to do. http://www.wccca.com/PITS/ Out of the 4 filters, two filters control the county field, and two filters control the call type field. but they all operate independently. How would I go about accomplishing this? Would I use NSPredicate to create a new array each time something is filtered or what? Thanks.
You could definitely use an NSPredicate for this. Probably the easiest thing to do would be to use the same IBAction for all four switches and have it do a recalculation:
- (IBAction)anySwitchDidChange:(id)sender
{
// make a set of all acceptable call types
NSMutableSet *acceptableCallTypes = [NSMutableSet set];
if(self.fSwitch.on) [acceptableCallTypes addObject:#"f"];
// ... etc, to create acceptableCallTypes and acceptableCounties
NSPredicate *predicate =
[NSPredicate predicateWithFormat:
#"(%# contains callType) and (%# contains county)",
acceptableCallTypes, acceptableCounties];
/*
this predicate assumes your objects have the properties 'callType' and
'county', and that you've filled the relevant sets with objects that would
match those properties via isEqual:, whether strings or numbers or
anything else.
NSDictionaries are acceptable since the internal mechanism used here is
key-value coding.
*/
NSArray *filteredArray = [_sourceArray filteredArrayUsingPredicate:predicate];
// send filteredArray to wherever it needs to go
}
Using predicateWithFormat: causes the text to be parsed right there and then. In this case that should be no problem whatsoever but in general you can create the predicates in advance and supply only the parameters at the relevant moment, should you ever end up using one in a really time critical area.
Im building an app where users will be able to filter through a set of photos based on 4 parameters:
model http://seismicdevelopment.com/shot.png
FeedType and PhotoType can be one of three possible values respectively. Market and Tag can contain multiple values that describe the photo. I have the ui setup where for FeedType/PhotoType is a series of UISwitches for each param. If you turn one value on, the others in that group will turn off.
Market/Tag have UIButtons that can be made selected/normal. Any selected button should be added to the filtering to narrow results.
I can't seem to figure out how I should write the filtering logic to be most effective. Essentially on any control change, I need to rewrite the predicate filter but I can't seem to wrap my head around how I can link the separate param filters together.
For Tag/Market I'd also like to add a disabled state for UIButtons that have no records, or no records based on the currently selected buttons.
It is hard to tell a precise advice without knowing what kind the parameters are, but, as far as i can see, you need to have four variables,more likely,NSStrings, and every time the user changes the parameter, you create a new fetch predicate, by appending all that variables with the right format. That's how i see it in general.
UPDATE
So, with Market and Tag Butons everything is quite obvious - you shoud use NSCompondPredicate. You'll need an array of predicates, so make a property.
#property (strong) NSMutableArray *subpredicates;
Then, each time user touches the button, you add or remove that narrowing predicate.
- (void)tagButtonTouched:(UIButton *)button
{
if (thisTagIsNotYetSelected)
[subpredicates addObject:[NSPredicate predicateWithFormat:#"ANY tags.name == %#", button.titleLabel.text]];//or some other predicate based on that button title
else
[subpredicates removeObject:[NSPredicate predicateWithFormat:#"ANY tags.name == %#",button.titleLabel.text] ]];
}
Same thing for Markets
- (void)marketButtonTouched:(UIButton *)button
{
if (thisMarketIsNotYetSelected)
[subpredicates addObject:[NSPredicate predicateWithFormat:#"ANY markets.name == %#", button.titleLabel.text]];//or some other predicate based on that button title
else
[subpredicates removeObject:[NSPredicate predicateWithFormat:#"ANY markets.name == %#",button.titleLabel.text] ]];
}
You should also add two variables,i guess,NSPredicates or NSString,that will hold the value of selected FeedType and PhotoType,lets's call them feedTypePredicate and photoTypePredicate respectivly. When user touches those switches(why not segmentedControls?), you just change their's values.
And, finally, you should just combine all those predicates into one and make your fetch!
if(photoTypePredicate)
[subpredicates addObject:photoTypePredicate];
if(feedTypePredicate)
[subpredicates addObject:feedTypePredicate];
NSPredicate *finished = [NSCompoundPredicate andPredicateWithSubpredicates:subpredicates];//Your final predicate