[R] How to apply vector value function to a multidimensional array indexed by the remaining dimensions?
Charles C. Berry
cberry at tajo.ucsd.edu
Fri Oct 1 23:57:07 CEST 2010
On Fri, 1 Oct 2010, yunjiangster wrote:
>
> Hi,
> I am looking for some generalization of colSums and rowSums for general
> vector valued functions, and for arrays of more than 2 dimensions.
> So as a concrete example, suppose I have a 3 dimensional array, given by x
> = array(1:100,c(3,4,5)).
> and I want to sum the 3rd index of x to obain a 3 by 4 matrix. Using rowSums
> would return a vector of length 3 because it treats the last two indices as
> a single index.
>
see the help page for colSums, esp. the 'dims' arg
> Besides summation, let's say if I define a vector valued function
> f<-function(x){min(x[1],min(x[2],x[3]))}, and I want to apply f to the last
> index of x, meaning for each 1<= i <= 3, 1<=j <=4, I want to compute
> f(x[i,j,]), and then put them in a 3 by 4 matrix. How would I be able to do
> that without using a for loop?
>
?apply
> thanks.
>
> Sincerely,
> John
> --
> View this message in context: http://r.789695.n4.nabble.com/How-to-apply-vector-value-function-to-a-multidimensional-array-indexed-by-the-remaining-dimensions-tp2937368p2937368.html
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>
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Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
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