From maechler at stat.math.ethz.ch  Tue Sep 13 17:55:28 2016
From: maechler at stat.math.ethz.ch (Martin Maechler)
Date: Tue, 13 Sep 2016 17:55:28 +0200
Subject: [Rd] R-intro: function 'stderr' and 'sd'
In-Reply-To: <1979148586.1732979.1473439921401@mail.yahoo.com>
References: <1979148586.1732979.1473439921401.ref@mail.yahoo.com>
	<1979148586.1732979.1473439921401@mail.yahoo.com>
Message-ID: <22488.8560.466832.88971@stat.math.ethz.ch>

>>>>> Suharto Anggono Suharto Anggono via R-devel <r-devel at r-project.org>
>>>>>     on Fri, 9 Sep 2016 16:52:01 +0000 writes:

    > In "An Introduction to R" Version 3.3.1, in "4.2 The function tapply() and ragged arrays", after
    > stderr <- function(x) sqrt(var(x)/length(x))  ,
    > there is a note in brackets:
    > Writing functions will be considered later in [Writing your own functions], and in this case was unnecessary as R also has a builtin function sd().

    > The part "in this case was unnecessary as R also has a builtin function sd()" is misleading. The builtin function sd() doesn't calculate standard error of the mean. It calculates standard deviation. The function 'stderr' can use 'sd':
    > function(x) sd(x)/sqrt(length(x))

You are right; thank you Suharto.
It now says

(Writing functions will be considered later in @ref{Writing your own
functions}.  Note that @R{}'s a builtin function @code{sd()} is something different.)



[Rd] R-intro: function 'stderr' and 'sd'
Martin Maechler