Re: BY with stdev?

[<Rich@mango-solutions.com>]

Hi Eva,

You need "tapply", not "by".  By is primarily used to split list-based structures by one or more factors.  The "tapply" function splits a vector by one or more factors ......

> by(fuel.frame$Mileage, fuel.frame$Type, mean)

INDICES:Compact

[1] 24.13333

---------------------------------------------------------------------------------------------------INDICES:Large

[1] 20.33333

---------------------------------------------------------------------------------------------------INDICES:Medium

[1] 21.76923

---------------------------------------------------------------------------------------------------INDICES:Small

[1] 31

---------------------------------------------------------------------------------------------------INDICES:Sporty

[1] 26

---------------------------------------------------------------------------------------------------INDICES:Van

[1] 18.85714

> by(fuel.frame$Mileage, fuel.frame$Type, stdev)

Problem in as.double: Cannot coerce mode list to double: list(c(27., 23., 26., 25., 24., 26., 24., 25., 21., 21., 23., 24., 23., 27., 23.))

Use traceback() to see the call stack

> tapply(fuel.frame$Mileage, fuel.frame$Type, mean)

  Compact    Large   Medium Small Sporty      Van

 24.13333 20.33333 21.76923    31     26 18.85714

> tapply(fuel.frame$Mileage, fuel.frame$Type, stdev)

  Compact    Large    Medium    Small   Sporty       Van

 1.884776 2.516611 0.9268087 3.807887 4.472136 0.8997354

Hope this helps,

Rich.

mangosolutions

R and S Consulting and Training

Tel   +44 118 902 6617

Fax  +44 118 902 6401

-----Original Message-----
From: s-news-owner@lists.biostat.wustl.edu [mailto:s-news-owner@lists.biostat.wustl.edu] On Behalf Of Eva Goldwater
Sent: 21 December 2004 18:28
To: s-news@lists.biostat.wustl.edu
Subject: [S] BY with stdev?

Hello,

I tried to get standard deviations for subgroups of a numeric column,

defined by another column. I'm using the by function, but it doesn't work

with stdev.  It's fine with mean or summarize, but not stdev or stderr.

Here is my test.  (This is S-Plus 6.2 on Windows.)

x <- data.frame(cbind(x1=rep(1:2,5), x2=runif(10)))

by(x$x2,x$x1,mean)

by(x$x2,x$x1,stdev)

 Problem in as.double: Cannot coerce mode list

 to double: list(c(0.361767916940153, 0.132468292489....

Use traceback() to see the call stack

by(x$x2,x$x1,stderr)

Problem in FUN(...X.sub.i...., str..: Too many

 arguments(1) in call to "FUN"; last 1 not matched

Use traceback() to see the call stack

What's the problem?  Incidentally, ?stderr takes me to help for the file()

function...

Thanks for your insights.  Eva

Eva Goldwater                           email: goldwater@schoolph.umass.edu

Biostatistics Consulting                Phone: (413) 545-2949

418 Arnold House                        Fax:   (413) 545-1645

715 North Pleasant Street

University of Massachusetts

Amherst, MA 01003-9304

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