Sha256: 19e35c9d0f56cb6d9754647ef7b113d7a3d14c498977d26e578f11ac1e488539
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Size: 1023 Bytes
Versions: 13
Compression:
Stored size: 1023 Bytes
Contents
module Alf
class Aggregator
#
# Defines a `variance()` aggregation operator.
#
# Example:
#
# # direct ruby usage
# Alf::Aggregator.variance{ qty }.aggregate(...)
#
# # lispy
# (summarize :supplies, [:sid], :total => variance{ qty })
#
class Variance < Aggregator
# Returns the least value.
#
# @see Aggregator::InstanceMethods#least
def least()
[0, 0.0, 0.0]
end
# Aggregates on a tuple occurence.
#
# @see Aggregator::InstanceMethods#_happens
def _happens(memo, val)
count, mean, m2 = memo
count += 1
delta = val - mean
mean += (delta / count)
m2 += delta*(val - mean)
[count, mean, m2]
end
# Finalizes the computation.
#
# @see Aggregator::InstanceMethods#finalize
def finalize(memo)
count, mean, m2 = memo
m2 / count
end
end # class Variance
end # class Aggregator
end # module Alf
Version data entries
13 entries across 13 versions & 2 rubygems