# [R] Loop Repetition

Bob O'Hara rn|@boh @end|ng |rom gm@||@com
Tue Aug 6 11:45:47 CEST 2019

```For a start, try this:

for(i in 1:5) {
x <- runif(4,0,1)
}

Which will do what you want, but will over-write x each time (so isn't
very good). Better (if you want to use the random numbers outside the
loop) is this:

x <- matrix(NA, nrow=5, ncol=4)
for(i in 1:5) {
x[i,] <- runif(4,0,1)
}

But better than this is not to use a loop at all, but to use R's vectorisation:

x <- matrix(runif(20,0,1), nrow=5, ncol=4)

i.e. generate a vector of random numbers (the runif()), and then put
that into a matrix (the matrix()).

Oh, and you could also do this:
replicate(5, runif(4, 0,1))
which is slightly odd here, but if you want to use the random numbers
to do something, you can do all of it in a function, e.g.

CalcMean <- function(n=4) {
x <- runif(n, 0, 1)
mean(x)
}
replicate(5, CalcMean(n=4))

Using a function makes code writing a lot easier, as you can write and
debug the function on its own, and then use replicate() to run the
loop (there are also functions like vapply() and apply() if you need
to pass different arguments into the function for different
iterations).

Bob

On Tue, 6 Aug 2019 at 11:28, Tolulope Adeagbo <tolulopeadeagbo using gmail.com> wrote:
>
> Thanks guys, I've tried all you're suggesting,  both for (x in 1:5) and
> break, but I cant seem to ascertain when the loop has generated a vector of
> 4 random numbers  5 times.
>
> On Tue, 6 Aug 2019, 10:09 Jim Lemon, <drjimlemon using gmail.com> wrote:
>
> > Hi Tolulope,
> > The "in" operator steps through each element of the vector on the
> > right. You only have one element. Therefore you probably want:
> >
> > for(x in 1:5)
> > ...
> >
> > Jim
> >
> > Jim
> >
> > On Tue, Aug 6, 2019 at 6:54 PM Tolulope Adeagbo
> > <tolulopeadeagbo using gmail.com> wrote:
> > >
> > > Hey guys,
> > >
> > > I'm trying to write a loop that will repeat an action for a stipulated
> > > number of times. I have written some code but i think i'm missing
> > something.
> > >
> > > for (x in 5) {
> > >
> > >   repeat{
> > >
> > >     x = runif(1:4, min = 0, max = 1)
> > >
> > >
> > >     print(x)
> > >
> > >
> > >     if (x== var_1[5]){
> > >
> > >       print("done")
> > >     }
> > >
> > >     print(x)}
> > > }
> > >
> > > The goal is to generate the random number 5 times.
> > >
> > >
> > >         [[alternative HTML version deleted]]
> > >
> > > ______________________________________________
> > > R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > > https://stat.ethz.ch/mailman/listinfo/r-help
> > http://www.R-project.org/posting-guide.html
> > > and provide commented, minimal, self-contained, reproducible code.
> >
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> and provide commented, minimal, self-contained, reproducible code.

--
Bob O'Hara
Institutt for matematiske fag
NTNU
7491 Trondheim
Norway

Mobile: +47 915 54 416
Journal of Negative Results - EEB: www.jnr-eeb.org

```