On 3/12/2012 10:47 AM, J Toll wrote:
Hi,
I have a problem that I'm finding a bit tricky. I'm trying to use
mapply and assign to generate curried functions. For example, if I
have the function divide
divide<- function(x, y) {
x / y
}
And I want the end result to be functionally equivalent to:
half<- function(x) divide(x, 2)
third<- function(x) divide(x, 3)
quarter<- function(x) divide(x, 4)
But I want to do it using mapply and assign:
mapply(assign,
c("half", "third", "quarter"),
lapply(2:4, function(i) {function(x) divide(x, i)}),
pos = 1)
The problem is with lazy argument evaluation/promises. i will be the
last value of i (in this case 4) for all instances. You can change that.
mapply(assign,
c("half", "third", "quarter"),
lapply(2:4, function(i) {force(i); function(x) divide(x, i)}),
pos = 1)
Note the inclusion of the force function. This gives expected results.
> half(12)
[1] 6
> third(12)
[1] 4
> quarter(12)
[1] 3
The problem is in the third line. I end up with 3 functions that are
all functionally equivalent to quarter(). Any suggestions on how to
get this to work properly.
Thanks.
James
--
Brian S. Diggs, PhD
Senior Research Associate, Department of Surgery
Oregon Health & Science University
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