[R] Applying a function to each element of an array

Prof Brian Ripley ripley at stats.ox.ac.uk
Fri Oct 7 21:28:17 CEST 2005

If A is the matrix the answer is 2*(1 - 2^(-A)), which took about 10secs 
for an example of your size.

>From \sum_{i=1}^n x^{1-i} = (1-x^{-n})/(1-x), E & OE.

On Fri, 7 Oct 2005, Tim Smith wrote:

> I have a 7000x7000 matrix, and each element is an integer. For each 
> element, I want to apply the function :
> wt <- 0
> for(q in 1:count){
> wt <- wt + 0.5^(q-1)
> }
> I get the value of 'count' from the elements in the matrix , and want to 
> store the corresponding 'wt' value for that element.
> I suppose I could loop through the matrix, and apply the function to 
> each element but this would take a really really long time. Are there 
> any quicker ways to get the same result?

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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