Statistics is a Foundation framework for calculating—no points for guessing it—statistics. It is inspired by Perl's Statistics::Descriptive and like it consists of two main classes.
SBStatistics calculates a range of statistical measurements on the fly as each data point is added. The data is then immediately discarded, giving it a very low memory footprint.
SBFullStatistics in turn subclasses SBStatistics and records each data point. It is therefore able to provide more advanced statistical functions. The trade-off is that it can consume a lot of memory if you are collecting a lot of data.
The following example assumes you have included the @p Statistics/Statistics.h header and somehow linked to the Statistics framework:
// Create statistics object
SBStatistics *stat = [SBStatistics new];
// Add some random data points
for (int i = 0; i < 1000; i++)
[stat addData:[NSNumber numberWithInt:random()/1000.0]];
// Format report
id fmt = [NSMutableArray array];
[fmt addObject:@"Data set consists of %u data points."];
[fmt addObject:@" * Min: %f"];
[fmt addObject:@" * Max: %f"];
[fmt addObject:@" * Mean: %f"];
[fmt addObject:@" * Variance: %f"];
[fmt addObject:@" * StdDev: %f"];
// Print it
NSLog([fmt componentsJoinedByString:@"\n"],
stat.count,
stat.min,
stat.max,
stat.mean,
[stat variance],
[stat standardDeviation]
);
The SBFullStatistics class can do other interesting stuff:
// Create statistics object
SBFullStatistics *stat = [SBFullStatistics new];
// Add some random data.
for (int i = 0; i < 1e4; i++)
[stat addData:[NSNumber numberWithDouble:random()]];
// Produce 10 equally-sized buckets covering the entire range
id buckets = [stat bucketsWithCount:10];
// Calculate frequency distributions.
id freq = [stat frequencyDistributionWithBuckets:buckets
cumulative:NO];
id cfreq = [stat frequencyDistributionWithBuckets:buckets
cumulative:YES];
// Iterate over the buckets and output the values
for (id bucket in buckets)
NSLog(@"%@ => %@ => %@",
bucket,
[freq objectForKey:bucket],
[cfreq objectForKey:bucket]);
Copyright (c) 2008, Stig Brautaset. All rights reserved.
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