39 lines
1.4 KiB
Factor
39 lines
1.4 KiB
Factor
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! Copyright (c) 2012 Anonymous
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! See http://factorcode.org/license.txt for BSD license.
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USING: accessors io kernel math math.functions math.parser
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sequences ;
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IN: rosetta-code.standard-deviation
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! http://rosettacode.org/wiki/Standard_deviation
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! Write a stateful function, class, generator or coroutine that
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! takes a series of floating point numbers, one at a time, and
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! returns the running standard deviation of the series. The task
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! implementation should use the most natural programming style of
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! those listed for the function in the implementation language;
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! the task must state which is being used. Do not apply Bessel's
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! correction; the returned standard deviation should always be
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! computed as if the sample seen so far is the entire population.
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! Use this to compute the standard deviation of this
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! demonstration set, {2,4,4,4,5,5,7,9}, which is 2.
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TUPLE: standard-deviator sum sum^2 n ;
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: <standard-deviator> ( -- standard-deviator )
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0.0 0.0 0 standard-deviator boa ;
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: current-std ( standard-deviator -- std )
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[ [ sum^2>> ] [ n>> ] bi / ]
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[ [ sum>> ] [ n>> ] bi / sq ] bi - sqrt ;
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: add-value ( value standard-deviator -- )
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[ nip [ 1 + ] change-n drop ]
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[ [ + ] change-sum drop ]
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[ [ [ sq ] dip + ] change-sum^2 drop ] 2tri ;
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: std-main ( -- )
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{ 2 4 4 4 5 5 7 9 }
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<standard-deviator> [ [ add-value ] curry each ] keep
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current-std number>string print ;
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