How can I extract part of the data with a selection criterion?
Hi, Try ab[a==3,] You're selecting only rows for which a==3 (before the comma), and all columns (empty condition for column index, after the comma) Patrick 2013/5/9 jpm miao <miaojpm at gmail.com>:
Hi, As an example, how can I get the data such that field a of ab, ab["a"], equals 3? I expect the answer to be the union of 2 and 4, as Thanks,
a<-c(1,3,4,3,5,6,5) b<-c(2,4,6,7,3,1,2) ab<-data.frame(a,b) ab
a b 1 1 2 2 3 4 3 4 6 4 3 7 5 5 3 6 6 1 7 5 2
ab[a==3]
Error in `[.data.frame`(ab, a == 3) : undefined columns selected
ab[ab["a"]==3]
[1] 3 3 4 7
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