R help - Oct 2014 - "inahull” from package alphahull not working when used with apply

Hi everyone,

I have a two column (x,y) database with say 20 million rows. I want to check the
points that are inside of a hull created with the package alphahull. The
function that does this is call ?inahull?, and it runs well when I use it for
one point at a time. But when I try to optimize the function using ?apply?, it
gives me the wrong results. I wonder what I am doing wrong? Below is the code: I
also wonder if "inahull", could be used in data.table?

library (alphahull)
DT<-data.frame(x=c(0.25,0.75,0.75,0.25),y=c(0.25,0.25,0.75,0.75))

#creates hull
HULL<-ahull(DT, alpha=0.5)

#generate two points as test
TEST<-data.frame(x=c(0.25,0.5),y=c(0.5,0.5))
TEST<-data.matrix(TEST)

#check individual points
InPoint1<-inahull(HULL, c(TEST[1,1],TEST[1,2]))
InPoint2<-inahull(HULL, c(TEST[2,1],TEST[2,2]))
> InPoint1
[1] FALSE
> InPoint2
[1] TRUE

#repead check using apply
in2D=apply(TEST, 1,function(x, y) inahull(HULL, p =
TEST))
> in2D
[1] FALSE FALSE





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On 27/10/14 06:05, Camilo Mora wrote:
> Hi everyone,
> 
> I have a two column (x,y) database with say 20 million rows. I want to
check the points that are inside of a hull created with the package alphahull.
The function that does this is call ?inahull?, and it runs well when I use it
for one point at a time. But when I try to optimize the function using ?apply?,
it gives me the wrong results. I wonder what I am doing wrong? Below is the
code: I also wonder if "inahull", could be used in data.table?
> 
> library (alphahull)
> DT<-data.frame(x=c(0.25,0.75,0.75,0.25),y=c(0.25,0.25,0.75,0.75))
> 
> #creates hull
> HULL<-ahull(DT, alpha=0.5)
> 
> #generate two points as test
> TEST<-data.frame(x=c(0.25,0.5),y=c(0.5,0.5))
> TEST<-data.matrix(TEST)
> 
> #check individual points
> InPoint1<-inahull(HULL, c(TEST[1,1],TEST[1,2]))
> InPoint2<-inahull(HULL, c(TEST[2,1],TEST[2,2]))
> 
>> InPoint1
> [1] FALSE
>> InPoint2
> [1] TRUE
> 
> #repead check using apply
> in2D=apply(TEST, 1,function(x, y) inahull(HULL, p = TEST))
Why do x or y not appear in the function expression?  Note that any
apply with a function that does not use its argument will give a
constant sequence.  Now also, apply gives the whole dimension as an
argument, so once you try to use y as an argument you will get the error
(I tried just to get the error correct):

    Error: argument "y" is missing, with no default

If that wasn't enough yet; let me ask another question, what is wrong
with p = TEST?

Best,
Bart
>> in2D
> [1] FALSE FALSE
> 
> 
> 
> 
> 
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> 
> 
> 
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