Statistics

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.

Examples

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]);

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License

Copyright (c) 2008-2013, Stig Brautaset. All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Author

• Stig Brautaset