[R] sapply and loop

[Roger D. Peng]

You can use system.time() to time your procedure.  There's no guarantee that 
sapply() will be faster than a for() loop, especially if you preallocate the 
matrices.

-roger

Zhen Pang wrote:

> Dear all,
> 
> I am doing 200 times simulation. For each time, I generate a matrix and 
> define some function on this matrix to get a 6 dimension vector as my 
> results.
> 
> As the loop should be slow, I generate 200 matrice first, and save them 
> into a list named ma,
> then I define zz<-sapply(ma, myfunction)
> 
> To my surprise, It almost costs me the same time to get my results if I 
> directly use a loop from 1 to 200. Is it common? Can I improve any further?
> 
> Ps, how to count the exact time to finish my code?
> 
> Thanks.
> 
> Zhen
> 
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-- 
Roger D. Peng
http://www.biostat.jhsph.edu/~rpeng/