[R] subsetting levels of a vector

[arun]

Hi,

Try this:
dat <- read.table(text="
ParticipID    ERP  Electrode
1        s1  0.0370      FP1
2        s2 35.0654      FP2
3        s3 -3.3852        F4
4        s4  2.6119        P3
5        s5  0.1224        P4
6        s6 -5.3153        O1
7        s7 -3.88          F4
8        s8  -4.988        FP1  

", header=TRUE)
str(d)

tomatch <- c("FP1", "FP2", "F4")
#You can use either one of these
dat[with(dat,Electrode%in%tomatch),]
dat[dat$Electrode%in%tomatch,]
#or
dat2<-within(dat,{Electrode=Electrode%in%tomatch})
dat[dat2$Electrode==TRUE,]
#  ParticipID     ERP Electrode
#1         s1  0.0370       FP1
#2         s2 35.0654       FP2
#3         s3 -3.3852        F4
#7         s7 -3.8800        F4
#8         s8 -4.9880       FP1

A.K.




----- Original Message -----
From: simona mancini <mancinisimona at yahoo.it>
To: "r-help at r-project.org" <r-help at r-project.org>
Cc: 
Sent: Friday, August 10, 2012 5:07 AM
Subject: [R] subsetting levels of a vector

Hi,


I need to subset different levels of vector in a dataset to create a new dataframe that contains only these. These observations are not numerical, so I can't use the subset() function (at least this is the response I get from R).
Suppose the dataframe looks like this:



  ParticipID    ERP   Electrode
1         s1  0.0370       FP1
2         s2 35.0654       FP2
3         s3 -3.3852        F4
4         s4  2.6119        P3
5         s5  0.1224        P4
6         s6 -5.3153        O1


I want to create a subset of the dataframe with only the FP1, FP2, F4 levels of Electrode, how do I do? 
(actually the levels I have to filter are much more than these three, but this is just to give an example).

I know this is a trivial question, but I am still getting familiar with R...

Thanks a lot,

s.

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