subsetting levels of a vector

-----Original Message-----
From: mancinisimona at yahoo.it
Sent: Fri, 10 Aug 2012 10:07:31 +0100 (BST)
To: r-help at r-project.org
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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