# [R] Testing for Inequality à la "select case"

diegol diegol81 at gmail.com
Mon Mar 16 04:46:39 CET 2009

```> That's what I meant by element-by -element. A vector in R corresponds
> to a row or a column in Excel, and a vector operation in R corresponds
> to a row or column of formulae, e.g.
>
> Excel
>      A      B       C
> 1)  5      10      a1+b1  (= 15)
> 2)  3       2       a2+b2  (= 5)
> etc.
>
> R
> A <- c(5,3)
> B <- c(10,2)
> C <- A + B

Steve, I still don't understand the analogy. I agree that in this case the R
approach is vectorized. However, your function just as you first proposed it
will not work without a loop.

> max and pmax are equivalent in this case.  I just use pmax as my
> default because it acts like other arithmetic operators (+, *, etc.)
> which perform pointwise (element-by-element) operations.

It's true. I changed it because I had applied your original version of mr()
to the entire vector x, which gave an incorrect result (perhaps "range" was
recycled in "idx <- which(x<=range)"). If I used max instead of pmax, and
ever happened to use mr() without a loop, the length of the result would be
strange enough for me to realise the error. But then again, I added the "if
(length(x) >1) stop("x must have length 1")" line, so using max or pmax now
doesn't really make a difference, apart perhaps from run time.

> Using cut/split seems like gross overkill here.  Among other things,
> you don't need to generate labels for all the different ranges.
>
>  which(x<=range)
> seems straightforward enough to me,

I could edit the mr_2() function a little bit to make it more efficient. I
left it mostly unchanged for the thread to be easier to follow. For example
I could replace the last four lines for only:

product <- x*percent
ifelse(product< minimum, minimum, product)

But I believe you refer to the cut/split functions rather. I agree that
"which(x<=range)" is straighforward, but using such expression will
require a loop to pull the trick, which I don't intend. Am I missing
something?

Regards,
Diego

Stavros Macrakis-2 wrote:
>
> Using cut/split seems like gross overkill here.  Among other things,
> you don't need to generate labels for all the different ranges.
>
>    which(x<=range)
>
> seems straightforward enough to me, but you could also use the
> built-in function findInterval.
>
>               -s
>
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> and provide commented, minimal, self-contained, reproducible code.
>
>

-----
~~~~~~~~~~~~~~~~~~~~~~~~~~
Diego Mazzeo
Actuarial Science Student