Issue with the R function rep()

Question

I am having an issue with the R function rep or maybe its something simpler that I am doing wrong.

    k = ((100)*(1-0.9))
    k # k = 10
    length(rep(0,times = k)) # length of 9 instead of 10
    length(rep(0,times = 10) # length of 10 !

This is really weird as the variable k has 10 as value.

Rich Scriven · Accepted Answer · 2017-01-21T02:05:31.013

Have a closer look at k. It's not an integer and it's also not really 10.

typeof(k)
# [1] "double"
print(k, digits = 22)
# [1] 9.999999999999998223643

We care about k being integer valued because the times argument of rep() should be an integer. Furthermore, from help(rep):

Non-integer values of times will be truncated towards zero.

So k becomes

trunc(k)
# [1] 9

See the link @Gregor left in the comments for why k is not really 10.

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