> LDL <- NA_real_
> is.LDL <- is.na
> v <- c(0.2, 0.28, LDL, 0.9)
> v
[1] 0.20 0.28   NA 0.90
> is.LDL(v)
[1] FALSE FALSE  TRUE FALSE
>

Hope this helps.

Chel Hee Lee

On 11/9/2014 12:07 PM, Marc Girondot wrote:
Dear member list,

In many experimental sciences, there is a lower detection limit (LDL) when a dosage of a product is done. Then some samples are evaluated to be below this limit. I search for the best way to indicate in a data.frame that some values are such LDL. Ideally, an equivalent of NA would be the best.
Until now I manage by indicating all the column in characters.
So the question is: is it possible to define a value that could be named LDL and that could take place in vectors or data.frame such as:
v <- c(0.2, 0.28, LDL, 0.9) is the same way that NA can be used.
with of course a function is.ldl(v) that would return F F T F

Thanks a lot for any direction to solve this

Marc

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