some R exercises

[UdVBIA]

Hi!

I tried everything to avoid asking somebody but I have absolutely no clue how to solve this tasks. I'll be really glad if someone could explain that to me...

1.



Well, the first part is of course no problem but I have really trouble with the tasks i) and ii). just don't know how to write the function and why I should use rexp...

2.


Oh I love loops. Well - "I think" I have to solve the first task to solve this...

Well there is more but I'll tried to fight with it a few more hours.

Thanks for helping!

[Florian Weiler]

On Exercise 5, how about this (I'm rather new to R as well, so no guarantee this is right and I'm sure there are more efficient ways to do this!):

fun1 <- function(x) {
  y <- 0
  for (i in 1:length(x))
      {y[i] <- (x[i]-mean(x))^2}
  sum(y)/(length(x)+1)
}

fun2 <- function(x) {
  y <- 0
  for (i in 1:length(x))
  {y[i] <- (x[i]-mean(x))^2}
  sum(y)/(length(x))
}

x <- rexp(15)
fun1(x)
fun2(x)

[Florian Weiler]

Just thought about it, you can have this of course "cheaper" without the loops. Like this:

fun1 <- function(x) sum((x-mean(x))^2)/(length(x)+1)
fun2 <- function(x) sum((x-mean(x))^2)/(length(x))

x <- rexp(15)
fun1(x)
fun2(x)

[Kenn Konstabel]

Hi,

But what if your professor reads this list?

Anyway, who cares, two hints:

1. It might be useful to read the explanations provided with the
problem. For example, your exercise tells you that "use the help
command ?rexp to read how to generate exponentially distributed
variables". On a careful reading, that may explain why they want you
to use rexp. Perhaps they want you to generate an exponentially
distributed variable?

2. If you're given an exercise on a topic that is not covered %in%
c(lectures, required.readings) and you can't figure it out by
yourself, maybe it would be useful to do some background reading
before you go on. You can find free books on R at
http://cran.r-project.org/other-docs.html . Or you could try
complaining the gray beard about asking you to do things he hasn't
taught you ... and then see what happens next.

Best regards,

K

On 5/9/12, UdVBIA <[hidden email]> wrote:

> Hi!
>
> I tried everything to avoid asking somebody but I have absolutely no clue
> how to solve this tasks. I'll be really glad if someone could explain that
> to me...
>
> 1.
>
> http://r.789695.n4.nabble.com/file/n4619850/task1.gif
>
> Well, the first part is of course no problem but I have really trouble with
> the tasks i) and ii). just don't know how to write the function and why I
> should use rexp...
>
> 2.
> http://r.789695.n4.nabble.com/file/n4619850/task2.gif
>
> Oh I love loops. Well - "I think" I have to solve the first task to solve
> this...
>
> Well there is more but I'll tried to fight with it a few more hours.
>
> Thanks for helping!
>
>
> --
> View this message in context:
> http://r.789695.n4.nabble.com/R-exercises-too-confusing-for-me-tp4619850.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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