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shoumikhin avatar shoumikhin commented on May 8, 2024

Sounds good, Yegor!

Could you please provide some use cases for such methods for different container types that we support (NSArray, NSSet, NSOrderedSet, NSDictionary)? May also like to implement them as test cases.

Thanks.

from functional-objc.

yegorsch avatar yegorsch commented on May 8, 2024

Here are some simple use cases.

- (void)testGroupByArray {
  // Arrange.
  NSArray<NSNumber *> *originalArray = @[ @5, @6, @7 ];
  NSDictionary<NSString *, NSArray<NSNumber *> *> *expectedDict = @{@"even" : @[ @6 ], @"odd": @[ @5,  @7 ]};

  // Act.
  NSDictionary<NSString *, NSArray<NSNumber *> *> *resultingDict= [originalArray fbl_groupby:^id(NSNumber *value) {
    if (value.integerValue % 2) {
      return @"odd";
    }
    return @"even";
  }];

  // Assert.
  XCTAssertEqualObjects(resultingDict, expectedDict);
}

- (void)testGroupByValueDictionary {
  // Arrange.
  NSDictionary<NSString *, NSNumber *> *originalDictionary = @{ @"one" : @12, @"two" : @40, @"three" : @13 };
  NSDictionary<NSString *, NSDictionary<NSString *, NSNumber *> *>
      *expectedDict = @{
        @"evenValues" : @{@"one" : @12, @"two" : @40},
        @"oddValues" : @{@"three" : @13}
      };

  // Act.
  NSDictionary<NSString *, NSDictionary<NSString *, NSNumber *> *>
      *resultingDict = [originalDictionary
          fbl_groupby:^NSString *(NSString *key, NSNumber *value) {
            if (value.integerValue % 2) {
              return @"oddValues";
            }
            return @"evenValues";
          }];

  // Assert.
  XCTAssertEqualObjects(resultingDict, expectedDict);
}

- (void)testGroupByOrderedSet {
  // Arrange.
  NSOrderedSet<NSNumber *> *originalOrderedSet =
      [NSOrderedSet orderedSetWithArray:@[ @13, @42, @0 ]];
  NSDictionary<NSString *, NSArray<NSNumber *> *> *expectedDict =
      @{ @"even" : @[ @42, @0 ],
         @"odd" : @[ @13 ] };

  // Act.
  NSDictionary<NSString *, NSArray<NSNumber *> *> *resultingDict = [originalOrderedSet fbl_groupby:^id(NSNumber *value) {
    if (value.integerValue % 2) {
      return @"odd";
    }
    return @"even";
  }];

  // Assert.
  XCTAssertEqualObjects(resultingDict, expectedDict);
}

- (void)testGroupBySet {
  // Arrange.
  NSSet<NSNumber *> *originalOrderedSet =
  [NSSet setWithArray:@[@13, @42, @0]];
  NSDictionary<NSString *, NSArray<NSNumber *> *> *expectedDict =
  @{ @"even" : @[ @42, @0 ],
     @"odd" : @[ @13 ] };

  // Act.
  NSDictionary<NSString *, NSArray<NSNumber *> *> *resultingDict = [originalOrderedSet fbl_groupby:^id(NSNumber *value) {
    if (value.integerValue % 2) {
      return @"odd";
    }
    return @"even";
  }];

  // Assert.
  XCTAssertEqualObjects(resultingDict, expectedDict);
}

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avatar commented on May 8, 2024

Hey Yegor,

Thank you for the sample unit tests!

Can you provide some use cases demonstrating when fbl_groupBy would be helpful in production code?

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yegorsch avatar yegorsch commented on May 8, 2024

Well, I have an example off the top of my head. Supposedly, we have an array of news models where each news instance has name, description, publisher and date. fbl_groupBy publisher, for example, would give us a dictionary of array of news with a corresponding publisher as a key. Keys can be further used to populate some sort of NewsFilterView where we can select publishers we are interested in.
Something like that:

  NSDictionary<NSString *, NSArray<News *> *> *newsByPublisherDictionary= [newsArray   NSDictionary<NSString *, NSArray<News *> *> *newsByPublisherDictionary =
      [newsArray fbl_groupBy:^NSString *(News *instance) {
        return instance.publisherName;
      }];

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shoumikhin avatar shoumikhin commented on May 8, 2024

Thank you for the examples, Yegor!

It seems like you're referring something like Dictionary's init(grouping:by:) constructor in Swift?
I believe if we wanted something similar in Objective-C, it should be implemented the same way, as:

+ (instancetype)dictionaryWithObjects:(NSArray<ObjectType> *)objects groupedBy:(id<NSCopying>(^)(ObjectType *))keyForValue

And this library provides just a subset of most popular functional primitives that followSequence methods, not a bunch of convenience initializers for NSDictionary, etc.

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yegorsch avatar yegorsch commented on May 8, 2024

Oh I see. Did not know about that one.

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