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Chapter 7. The normal and sampling densities

Scripts:

areas-under-the-normal.R (add comments, etc. here)
cardiac.R (add comments, etc. here)
compare-normals.R (add comments, etc. here)
data-transformations.R (add comments, etc. here)
excercise-sampling-distribution.R (add comments, etc. here)
excercise-stiatistics-of-sampling-distribution.R (add comments, etc. here)
excercise-transformation.R (add comments, etc. here)
exercise-brown-bat.R (add comments, etc. here)
exercise-normal.R (add comments, etc. here)
expectation-variance-normal.R (add comments, etc. here)
kruger.R (add comments, etc. here)
midterm-K-S-test.R (add comments, etc. here)
normal-binomial-approximation.R (add comments, etc. here)
normal-discrete-approximation.R (add comments, etc. here)
normal-Poisson-approximation.R (add comments, etc. here)
normal-scores.R (add comments, etc. here)
normal.R (add comments, etc. here)
QQ-normal-beta-centered.R (add comments, etc. here)
QQ-normal-beta-left.R (add comments, etc. here)
QQ-normal-beta-right.R (add comments, etc. here)
QQ-normal-normal.R (add comments, etc. here)
sampling-density-intensity-murders-south.R (add comments, etc. here)
sampling-density-of-mean-Iraq.R (add comments, etc. here)
sampling-density-of-proportion-West-Bank.R (add comments, etc. here)
sampling-density-of-variance.R (add comments, etc. here)

Data:

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ljrqxktnc kxnpm ? — 27 August 2008, 08:44

eqos ughmc yepz wrgp digtu nybi oyflcq

Douglas Bates — 20 December 2008, 14:17

I was unable to add a comment to the sampling-density-of-variance.R script discussion so I will add it here.

As I mentioned to Yosef, the fact that the first loop is slower than the others is almost entirely due to the vector v being initialized to a vector of length zero. If you replace the function s.loop with

s.loop1 <- function(R, n){ set.seed(10) v <- numeric(R) for(i in 1 : R) v[i] <- var(rexp(n)) v }

you will find that its speed is competitive with the others. The idiom that I prefer to teach is

set.seed(10) v <- replicate(R, var(rexp(n)))

It is also competitive in speed and I think it is more intuitive.

Douglas Bates — 20 December 2008, 14:19

I keep forgetting that this Wiki doesn't maintain line breaks. Without line breaks those samples of code should be

s.loop1 <- function(R, n){set.seed(10); v <- numeric(R); for(i in 1 : R) v[i] <- var(rexp(n)); v}

and

set.seed(10); v <- replicate(R, var(rexp(n)))

Page last modified on December 20, 2008, at 02:19 PM