[SOLVED] How to group HKStatistics by hour?

How to group HKStatistics by hour?

I'm trying to extract step data from HealthKit.

I want to create a summary of step data grouped by hour. Currently, I can extract all of the samples of data between a date range provided by NSPredicate with HKSampleQuery. I could also get a sum of the step count between a date range with HKStatisticsQuery.

What I am asking is if there is a way to sum group the samples or statistics by hour. In SQL I would write something like this:

SELECT HOUR(date), SUM(steps) FROM healthkit WHERE date BETWEEN 'blah' AND 'blah' GROUP BY 1;

Am I seriously going to have to query HKStatistics 24 x 31 times to write the last month of step data grouped by hour? Because that seems rather inefficient, especially with how the resultsHandler is implemented.

Solution

You should use an HKStatisticsCollectionQuery where you can perform grouping by time intervals. An example stub code would be:

NSDate *startDate, *endDate, *anchorDate; // Whatever you need in your case    
HKQuantityType *type = [HKObjectType quantityTypeForIdentifier:HKQuantityTypeIdentifierStepCount];

// Your interval: sum by hour
NSDateComponents *intervalComponents = [[NSDateComponents alloc] init];
intervalComponents.hour = 1;

// Example predicate
NSPredicate *predicate = [HKQuery predicateForSamplesWithStartDate:fromDate endDate:toDate options:HKQueryOptionStrictStartDate];

HKStatisticsCollectionQuery *query = [[HKStatisticsCollectionQuery alloc] initWithQuantityType:type quantitySamplePredicate:predicate options:HKStatisticsOptionCumulativeSum anchorDate:anchorDate intervalComponents:intervalComponents];
    query.initialResultsHandler = ^(HKStatisticsCollectionQuery *query, HKStatisticsCollection *result, NSError *error) {
        // do something with the results
    };
[healthStore executeQuery:query];

You can read more details in the HKStatisticsCollectionQuery docs