How to test whether a vector contains repetitive elements?

I think I found the answer. Use duplicated() function:

a=c(3,5,7,2,7,9)
b=1:10
any(duplicated(a)) #True
any(duplicated(b)) #False

Also try rle(x) to find the lengths of runs of identical values in x.

If you're looking for consecutive repeats you can use diff.

a <- 1:10
b <- c(1:5, 5, 7, 8, 9, 10)
diff(a)
diff(b)

Or anywhere in the vector:

length(a) == length(unique(a))
length(b) == length(unique(b))

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