# [R] Pseudo-random numbers between two numbers

(Ted Harding) Ted.Harding at manchester.ac.uk
Wed Mar 11 20:48:14 CET 2009

```Because of a mistake I made in copying code into email, there has
been confusion (expressed in some private emails). Hence the
corrected version is appended at the end.

On 11-Mar-09 00:05:26, Ted Harding wrote:
> I have modified my example to make it more convincing! See at end.
>
> On 10-Mar-09 23:39:17, Ted Harding wrote:
>> On 10-Mar-09 23:01:45, guox at ucalgary.ca wrote:
>>> Please forget the last email I sent with the same subject.
>>> =================
>>> I would like to generate pseudo-random numbers between two numbers
>>> using R, up to a given distribution, for instance, norm. That is
>>> something like
>>> rnorm(HowMany,Min,Max,mean,sd)
>>> over rnorm(HowMany,mean,sd).
>>> I am wondering if
>>>
>>> qnorm(runif(HowMany, pnorm(Min,mean,sd), pnorm(Max,mean, sd)),
>>>       mean, sd)
>>>
>>> is good. Any idea? Thanks.
>>> -james
>>
>> It would certainly work as intended! For instance:
>>
>> truncnorm<-function(HowMany,Min,Max,mean=0,sd=1){
>>   qnorm(runif(HowMany, pnorm(Min,mean,sd), pnorm(Max,mean, sd)),
>>         mean, sd)}
>> Sample <- truncnorm(1000,-1,2.5)
>> hist(Sample,breaks=100)
>>
>> Hoping this helps,
>> Ted.
>
> truncnorm<-function(HowMany,Min,Max,mean=0,sd=1){
>   qnorm(runif(HowMany, pnorm(Min,mean,sd), pnorm(Max,mean, sd)),
>         mean, sd)}
> Sample <- truncnorm(100000,-1,2.5)
> hist(Sample,breaks=100)
> u0<-(-0.975)+0.05*(0:69)
> yy<-dnorm(u0)
> du<-min(diff(H\$breaks))
> Y <- 100000*yy*du/(pnorm(2.5)-pnorm(-1.0))
> lines(u0,Y)
>
> Ted.

Corrected version:
------------------

truncnorm<-function(HowMany,Min,Max,mean=0,sd=1){
qnorm(runif(HowMany, pnorm(Min,mean,sd), pnorm(Max,mean, sd)),
mean, sd)}
Sample <- truncnorm(100000,-1,2.5)
H <- hist(Sample,breaks=100)
u0<-(-0.975)+0.05*(0:69)
yy<-dnorm(u0)
du<-min(diff(H\$breaks))
Y <- 100000*yy*du/(pnorm(2.5)-pnorm(-1.0))
lines(u0,Y)

Apologies for the error.
Ted.

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E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
Fax-to-email: +44 (0)870 094 0861
Date: 11-Mar-09                                       Time: 19:48:12
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