Cumulative standard deviation: Difference between revisions
restored R and Racket
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Line 2,726:
>>> print myStd([2,4,4,4,5,5,7,9])
2.0
</lang>
=={{header|R}}==
===Built-in Std Dev fn===
<lang rsplus>#The built-in standard deviation function applies the Bessel correction. To reverse this, we can apply an uncorrection.
#If na.rm is true, missing data points (NA values) are removed.
reverseBesselCorrection <- function(x, na.rm=FALSE)
{
if(na.rm) x <- x[!is.na(x)]
len <- length(x)
if(len < 2) stop("2 or more data points required")
sqrt((len-1)/len)
}
testdata <- c(2,4,4,4,5,5,7,9)
reverseBesselCorrection(testdata)*sd(testdata) #2</lang>
===From scratch===
<lang rsplus>#Again, if na.rm is true, missing data points (NA values) are removed.
uncorrectedsd <- function(x, na.rm=FALSE)
{
len <- length(x)
if(len < 2) stop("2 or more data points required")
mu <- mean(x, na.rm=na.rm)
ssq <- sum((x - mu)^2, na.rm=na.rm)
usd <- sqrt(ssq/len)
usd
}
uncorrectedsd(testdata) #2</lang>
=={{header|Racket}}==
<lang racket>
#lang racket
(require math)
(define running-stddev
(let ([ns '()])
(λ(n) (set! ns (cons n ns)) (stddev ns))))
;; run it on each number, return the last result
(last (map running-stddev '(2 4 4 4 5 5 7 9)))
</lang>
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