Latest 0.9
License MIT
Platforms ios 7.0, osx 10.8, requires ARC

Build Status
Carthage compatible
Pod Information

MogKit is a toolkit that provides fully tested and easily composable transformations to collections and any series of values (like signals, channels, etc). The transformations are independant of the underlying values or data structures which makes them highly reusable.

As opposed to similar transformation frameworks MogKit works with composition instead of chaining which means the values are only iterated over once instead of once per step.

Use cases

There are several cases where using MogKit might make sense. Easiest shown with some example.

Simply transform data

When you simply want to transform some data in for example an array into a new array.

NSArray *array = @[@1, @2, @3];
NSArray *result = [array mog_transform:MOGMap(^id(NSNumber *number) {
    return @(number.intValue + 100);

// result is now @[@101, @102, @103]

Or work on some numbers and output as a string:

NSArray *array = @[@1, @2, @3];

NSString *result = MOGTransform(array, MOGStringConcatReducer(@", "), MOGCompose(MOGMap(^id(NSNumber *val) {
    return @(val.intValue + 10);
}), MOGMap(^id(NSNumber *val) {
    return val.stringValue;

// result = "11, 12, 13"

It can also be used on any NSObject like:

id object = @10;
NSArray *expected = @[@(-10), @0, @10];

NSArray *result = [object mog_transform:MOGFlatMap(^id(NSNumber *number) {
    return @[@(-number.intValue), @0, number];
}) reducer:MOGArrayReducer()];

// result = @[@(-10), @0, @10]

Use to easily implement some transformation functions

Another case is when you have some data structure and want to add a transformation method to it, for example extending NSArray and give it a filter method, all you need to do is

@implementation NSArray (Filterable)

- (NSArray *)filter:(MOGPredicate)predicate
    return [self mog_transform:MOGFilter(predicate)];


Combine to create new transformations

Say you want to add a trim: method to NSArray that returns a new array with trimSize elements removed from the start and end.

- (NSArray *)trim:(NSUInteger)trimSize 
    return [self mog_transform:MOGCompose(MOGDrop(trimSize), MOGTake(self.count - 2 * trimSize))];

Non-collection use cases

Using MogKit isn’t limited to containers implementing NSFastEnumeration. You can easily make use of it to add composable transformation to anything where you want to transform a set of values. Here is an example adding a -mog_transform: method to RACStream (from ReactiveCocoa) in order to apply the passed in transformation to all values on the stream. This can be used instead of chaining a several of RACStreams built in transformations.

@implementation RACStream (MogKit)

- (instancetype)mog_transform:(MOGTransformation)transformation
    Class class = self.class;

    MOGTransformation transformationWithMapToRAC = MOGCompose(transformation, MOGMap(^id(id val) {
        return [class return:val];

    MOGReducer *reducer = transformationWithMapToRAC(MOGArrayReducer());

    return [[self bind:^{
        return ^(id value, BOOL *stop) {
            id acc = reducer.reduce(reducer.initial(), value, stop);
            if (*stop) {
                acc = reducer.complete(acc);
            return [class concat:acc];
    }] setNameWithFormat:@"[%@] -mog_transform:",];


This can later be used to apply a transformation to all values in a channel like this:

NSNumberFormatter *currencyFormatter = [NSNumberFormatter new];
currencyFormatter.numberStyle = NSNumberFormatterCurrencyStyle;

MOGTransformation add100ToIntValuesAndFormatAsCurrency = MOGComposeArray(@[
    MOGMap(^id(NSString *string) {
        return @([string intValue] + 100);
    MOGMap(^id(id val) {
        return [currencyFormatter stringFromNumber:val];

[[textField.rac_textSignal mog_transform:add100ToIntValuesAndFormatAsCurrency] subscribeNext:^(id x) {
    NSLog(@"Number plus 100 = %@", x);

The transformation can then be reused and is not even tied to RACStream.

Implemented Transformations

  • Map
  • Filter
  • Remove
  • Take
  • TakeWhile
  • TakeNth
  • Drop
  • DropWhile
  • DropNil
  • Replace
  • ReplaceWithDefault
  • MapDropNil
  • Unique
  • Dedupe
  • Flatten
  • FlatMap
  • PartitionBy
  • Partition
  • Window



The easiest way is to install through Carthage. Simply add

github "mhallendal/MogKit"

to your Cartfile and follow the Carthage instructions for including the framework in your application.


Alternatively by using CocoaPods, simply add

pod 'MogKit'

to your Podfile.


You can also add it as submodule to your project and include the project file in your application.

If you are using the Foundation extensions, like -mog_transform: on NSArray, make sure that you add -ObjC to your application’s Other Linker Flags.


  • Swift support (post 1.0)


The API is still not locked down so might change slightly until 1.0 has been released.

This looks like Transducers

For a reader that are familiar with Transducers this will feel familiar, MogKit is implemented using Transducers and MOGTrasformations are actually transducers mapping from MOGReducer to MOGReducer.

For an introduction to transducers, see Clojure – Transducers and the presentation by Clojure creator Rich Hickey.

Latest podspec

    "name": "MogKit",
    "version": "0.9",
    "summary": "MogKit is a transducer based data transformation toolkit for Objective-C.",
    "description": "                   A longer description of MogKit in Markdown format.nn                   MogKit is a toolkit that provides fully tested and easily composable transformationsn                   to collections and any series of values (like signals, channels, etc). Then                   transformations are independant of the underlying values or data structures whichn                   makes them highly reusable.nn                   MogKit composes transformations instead of chaining them which means collectionsn                   will only be passed through once.n",
    "homepage": "",
    "license": {
        "type": "MIT",
        "file": "LICENSE"
    "authors": {
        "Mikael Hallendal": "[email protected]"
    "platforms": {
        "ios": "7.0",
        "osx": "10.8"
    "source": {
        "git": "",
        "tag": "0.9"
    "source_files": "MogKit/*.{h,m}",
    "public_header_files": "MogKit/*.h",
    "requires_arc": true

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