Testing for Inequality à la "select case"

...Steve, ...
Actually Stavros (???????), not Stephen/Steve (????????).  Both Greek,
but different names.
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.
Approach is vectorized over the range parameter, but not vectorized
over the x parameter.  If you want to vectorize over x, you can use
findInterval:

mr <-
 local({
   # Local constants
   range= c(0,20,100,250,700,1000,Inf)*1000
   perc = c(65,40,30,25,20,0)/100
   min =  c(0,14,40,75,175,250)*1000

   function(x)
     { idx <- findInterval(x,range)
       pmax( x*perc[idx], min[idx] )
     }
 })

And this time, you *do* need pmax.  I did refer to cut/split, but only
to say they were unnecessary.

          -s
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)[1]"). 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)[1]
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)[1]" 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)[1]

seems straightforward enough to me, but you could also use the
built-in function findInterval.

              -s

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-----
~~~~~~~~~~~~~~~~~~~~~~~~~~
Diego Mazzeo
Actuarial Science Student
Facultad de Ciencias Econ?micas
Universidad de Buenos Aires
Buenos Aires, Argentina
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Testing for Inequality à la "select case"

Thread (11 messages)