[R] RES: another aov results interpretation question

[Paulo Brando]

Dear All,

I created a script to calculate averages - two groups: "parcel" and
"date" - and, based on these averages, make a graph. The problem is that
'R' does not recognize the first column even if I try to insert one. 

A brief example

Raw data: 

Data <- sample(1:100, 30, replace = FALSE, prob = NULL)
Date <- rep(c("02/30/2004","03/15/2004", "04/16/2004", "06/14/2004",
"07/08/2004"), 6)
Parcel <- rep(c("DRY", "CONTROL"),15)

Df <- data.frame(Parcel, Date, Data)

Res <- tapply(Df$Data, list(Date = Df$Date, Parcel = Df$Parcel), mean) 


> Res
            Parcel
Date          CONTROL      DRY
  02/30/2004 53.00000 52.33333
  03/15/2004 54.00000 67.66667
  04/16/2004 54.66667 30.00000
  06/14/2004 27.66667 20.00000
  07/08/2004 59.00000 38.00000

> colnames(Res)
[1] "CONTROL" "DRY"

> matplot(Res[,1], Res[,-1], type = "l") 

### It does not recognize the colunm "Date". Why?

Thanks in advance!

Paulo

________________________________________
Paulo M. Brando
Instituto de Pesquisa Ambiental da Amazonia (IPAM)
Santarem, PA, Brasil.
Av. Rui Barbosa, 136.
Fone: + 55 93 522 55 38
www.ipam.org.br
E-mail: pmbrando at ipam.org.br