[R] Combining tapply() and cor.test()?

[Dimitris Rizopoulos]

one approach is the following:

dat <- data.frame(
    Period = as.Date(rep(c("1996-07-31", "1996-08-31", "1996-09-30"), 
each = 15)),
    Returns = rnorm(45),
    MFR.Factor = runif(45)
)

###########

do.call(rbind, lapply(split(dat[c("Returns", "MFR.Factor")], 
dat$Period),
    function (x) {
        cr <- cor.test(x$Returns, x$MFR.Factor, method = "spearman")
        c("estimate" = cr$estimate, "p.value" = cr$p.value)
}))


I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://med.kuleuven.be/biostat/
     http://www.student.kuleuven.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "Sergey Goriatchev" <sergeyg at gmail.com>
To: <r-help at stat.math.ethz.ch>
Sent: Thursday, February 22, 2007 2:35 PM
Subject: [R] Combining tapply() and cor.test()?


> Hello, fellow R-users.
>
> Let me describe the setup first. I have a data.frame, a sample of
> which is reported below:
>
>           Company.Name      Periods      Returns   MFR.Factor
> 350         Wartsila Oyj A      1996-07-31      6.82         0.02
> 351    Custodia Holding AG  1996-07-31      4.15        -0.02
> 352           Wartsila Oyj       1996-07-31      7.73         0.09
> 353           GEA Group AG   1996-07-31    10.12         0.04
> 354            LEGRAND ORD 1996-07-31     -7.46        -0.20
> 355 Mayr-Melnhof Karton AG 1996-07-31     4.71        -0.05
> 356            GEVAERT NPV  1996-08-30      NA          NA
> 357        NOKIA K FMA2.50  1996-08-30     7.65         0.03
> 358           Altadis S.A.         1996-08-30     7.65         0.55
> 359       Metrovacesa S.A.     1996-08-30     4.55        -0.17
> 360               Oce N.V.          1996-08-30    9.43         0.23
>
> The variable "Periods" is a date object, shows the month.
> Variables "Returns" and "MFR.Factor" are numeric.
> For each month the number of Returns and MFR.Factors varies, 
> sometimes
> it is 350, sometimes 320 etc.
>
> What I need is to use cor.test(Returns, MFR.Factor,...) for each
> month, and produce a dataframe with columns: "Period", 
> "cor.estimate",
> "p.value".
>
> The simplest way would be with tapply() using variable "Period" as a
> factor, but tapply() only applies FUN to just one cell.
>
> What is the most painless way to achieve my objective?
>
> Thank you in advance for your help!
>
> Best,
> Sergey
>
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> 


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