[R] How to get the duplicated elements from a vector?
iverson at biostat.wisc.edu
Wed Oct 29 15:45:22 CET 2008
Leon Yee wrote:
> Gustaf Rydevik wrote:
>> Hi Leon,
>> should work, depending on what you want.
> Thank you all. Actually, I have a data frame or matrix, whose first
> column is numerical values, and whose 2nd column is names.
Then you have a data.frame, as matrices in R are of homogeneous type.
>I need those
> whose names repeated 3 times and get the mean of the 3 values for each
> repeated names.
> It sounds that I need some programming work.
Yes, but not much
## BEGIN R CODE
## guarantees there is at least one level with exactly three elements,
## which your problem seems to require
t1 <- data.frame(a = rnorm(10), b = c("D", "D", "D",
sample(LETTERS[1:3], 7, replace = TRUE)))
## find which names have exactly three elements
t2 <- subset(t1, b %in% names(which(table(t1$b) == 3)))
## note that the elements of the returned value depend on what was
## originally in your data set's 'b' column
tapply(t2$a, t2$b, mean)
## END R CODE
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