On Aug 19, 2012, at 5:14 PM, Dikán Szabolcs András wrote:

Dear R Users! I&#39;m new in R! I&#39;ve got a data.frame. For example:a<-data.frame(cbind( 0:1, 1:10)) X1 X2
1   0  1
2   1  2
3   0  3
4   1  4
5   0  5
6   1  6
7   0  7
8   1  8
9   0  9
10 1 10 Firstly i want to create combinations from X2, for example:combn(a$X2,2) It&#39;s ok,
but secondly



I would like to get combinations from those X2 numbers only , where X1= 0. Could you help me? Thanks!

> combn( a[a$X1==0, "X2"] ,2)
     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,]    1    1    1    1    3    3    3    5    5     7
[2,]    3    5    7    9    5    7    9    7    9     9


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Please learn to post with a meaningful subject line and in plain text. The most excellent Posting Guide is a font of wisdom in other areas as well. As is the "Introduction to R" which should be studied in its entirety but for this case the section: "2.7 Index vectors; selecting and modifying subsets of a data set".


Afore-mentioned posting guide: http://www.R-project.org/posting-guide.html

--

David Winsemius, MD
Alameda, CA, USA

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