On Sep 29, 2009, at 2:36 PM, Jarek Jasiewicz wrote:
well function arguments are in square brackets. z is result (new
vector). I show Matematica syntax, but cannot explain what I expect.
Sorry
The example is wrong because it can be replaced by R cut function.
The arguments are: condition,action.... and can be replaced by ste
of ifelse formulas:
if (x<10) x<-0.7
else if (x<30 && x=>10) x<-x^2/(x-1)
etc...
but that solution is slow for vectors with millions of numbers
1)Slow? It shouldn't even work! The if { } else { } construct is for
program control, not for iterative testing and assignment. You should
be using ifelse(<cond>, <affirm-val>, <neg-val>) which is designed for
that purpose.
2) you should not be using "&&" unless you are working with a scalar.
Use "&".
Perhaps (minimally tested):
x <- 1:100
ifelse( x < 10, 0.7, ifelse( x<30 & x>=10, x^2/(x-1), NA))
(And the "x >= 10" , (I doubted that " =>" would be correct and
testing shows it does throw a syntax error), is not needed since you
would never get to that evaluation if x were < 10.
Note: the ifelse's can be only nested up to 7 levels if memory serves.
--
David
thanks
Jarek
Erik Iverson pisze:
Hello,
I'm looking for equivalent of Matematica function "Which" which
works as
follows:
z = Which[x<10,0.3, 10<=x<20,0.5, 20<=x<100,1]
where x is a vector
Unless someone happens to be a Mathematica user (very possible), I
don't know how we would answer the question. You give an example
of the function call, but not what the function arguments or return
value are.
There is an R function called "which", but what the Mathematica
"Which" is doing is entirely mysterious from your example. What is
in "z" for instance??
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