[R] need indexing help again

[bunny , lautloscrew.com]

Dear all,


i have a problem which deals with indexing again, i guess.
I am a beginner and though i read the S Poetry stuff it is not that  
easy for me
to use the examples for my problems, maybe all this needs some  
practice...

Here´s the question. As i want to perform a factor analysis i need  
the same number of rows for every column to get a matrix that i use  
as an argument of factanal.
I´d like to find out which of 5 question i asked explain the variance  
in my dataset.
People were able to choose "dont know".
Of course someone who didn´t know, could know the answers for the  
other question.

To put in a nutshell,  only those results are valid for my factanal  
in which every question is answered (which is ok, as it is that way  
most of the time).
i have matrices  question1, question2 etc which contain the answers  
to each question.
Every person has a result id.

There fore my idea is to put all the matrices into one big matrices  
and then just take those of out the matrices, where the resultid  
occurs 5 times - as i have 5 questions.


And here are my two questions :

  a) is there some syntax that  helps me with:
if number of any resultid appearance in column 1 is is smaller than  
5, dont put it into my new matrix ?

b) is the idea in general wrong ? is there an easier way to get the  
matrices into one.. prepared for a factanal ?


thx in advance!

matthias