Example.md

Example: Alpha trimmed mean filter

Here is an example that shows some of the reusability by creating processes that are agnostic to the underlying data structures or how the results are collected, a reusable alpha trimmed mean filter:

MOGTransformation Trim(NSUInteger drop, NSUInteger finalSize)
{
    return MOGCompose(MOGDrop(drop), MOGTake(finalSize));
}

MOGMapFunc SortArrayOfNumbers(BOOL ascending)
{
    NSSortDescriptor *lowestToHighest = [NSSortDescriptor sortDescriptorWithKey:@"self" ascending:ascending];

    return ^id(NSArray *numbers) {
        return [numbers sortedArrayUsingDescriptors:@[lowestToHighest]];
    };
}

MOGMapFunc TrimArray(NSUInteger trimN)
{
    return ^id(NSArray *values) {
        return [values mog_transduce:TrimTransducer(trimN, values.count - 2 * trimN)];
    };
}

MOGMapFunc MeanOfArrayOfNumbers()
{
    return ^id(NSArray *numbers) {
        return [numbers valueForKeyPath:@"@avg.self"];
    };
}

MOGTransformation AlphaTrimmedMeanFilter(NSUInteger windowSize)
{
    return MOGComposeArray(@[
        MOGWindow(windowSize),
        MOGMap(SortArrayOfNumbers(YES)),
        MOGMap(TrimArray(windowSize / 4)),
        MOGMap(MeanOfArrayOfNumbers())
    ]);
}

// This filter can now be used in a number of different ways

NSArray *array = @[@14, @13, @12, @1, @2, @3, @4, @5, @15, @9, @8, @7, @13, @14];

MOGTransformation filter = AlphaTrimmedMeanFilter(12);

NSArray *result = [array mog_transform:filter];
// result == [14, 14, 14, 14, 13.83, 13.5, 11.83, 10.33, 10.33, 9.5, 8.5, 7.5, 7.5, 7.5]

// By using a different reduce function it's easy to only get the last value:
NSNumber *number = MOGTransform(array, MOGLastValueReducer(), @0, filter);
// number == 7.5

// Or we can simulate the numbers coming in from a stream and manually feed numbers to the filter.
MOGMapFunc manualFilter = MOGValueTransformer(filter);

number = manualFilter(@14); // number == 14
number = manualFilter(@13); // number == 14
number = manualFilter(@12); // number == 14
number = manualFilter(@1);  // number == 14
number = manualFilter(@2);  // number == 13.83