R help - Jan 2008 - Avoiding FOR loops

useR's,

I would like to know if there is a way to avoid using FOR loops to perform
the below calculation. 

Consider the following data:
> x
     [,1] [,2] [,3]
[1,]    4   11    1
[2,]    1    9    2
[3,]    7    3    3
[4,]    3    6    4
[5,]    6    8    5
> xk
     Var1  Var2 Var3
1   -0.25  1.75  0.5
2    0.75  1.75  0.5
3    1.75  1.75  0.5
4    2.75  1.75  0.5
5    3.75  1.75  0.5
6    4.75  1.75  0.5
7    5.75  1.75  0.5
8    6.75  1.75  0.5
9    7.75  1.75  0.5
10  -0.25  2.75  0.5

Here, X is a matrix of 3 variables in which each is of size 5 and XK are
some values that correspond to each variable.  For each variable, I want to
do:

|Xi - xkj|   where i = 1 to 3 and j = 1 to 10

It looks as if a double FOR loop would work, but can the apply function
work?  Or some other function that is shorter than a FOR loop?  Thank you, I
hope this makes sense.

Derek


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On Jan 6, 2008, at 7:55 PM, dxc13 wrote:
>
> useR's,
>
> I would like to know if there is a way to avoid using FOR loops to  
> perform
> the below calculation.
>
> Consider the following data:
>
snip
> Here, X is a matrix of 3 variables in which each is of size 5 and  
> XK are
> some values that correspond to each variable.  For each variable, I  
> want to
> do:
>
> |Xi - xkj|   where i = 1 to 3 and j = 1 to 10
>
That should be i=1 to 5 I take it?

If I understand what you want to do, then the outer function is the key:

lapply(1:3, function(i) { outer(x[,i], xk[,i],  "-") } )

This should land you with a list of three 5x10 tables
> It looks as if a double FOR loop would work, but can the apply  
> function
> work?  Or some other function that is shorter than a FOR loop?   
> Thank you, I
> hope this makes sense.
>
> Derek
>
Haris Skiadas
Department of Mathematics and Computer Science
Hanover College