R help - Aug 2016 - generate a vector of random numbers within confines of certain parameters

Dear group,

I am trying to generate a vector of random numbers for 20K observation.

however, I want to generate numbers (with 6 decimal places) within the range of
Std. Dev : 2-3
mean  : 4-6

Is there a method to generate numbers with 6 decimal places under
these parameters

thank you.
Adrian

Try
> set.seed(42)
> x1 <- round(rnorm(20000, 4, 2), 6)
> head(x1)
[1] 6.741917 2.870604 4.726257 5.265725 4.808537 3.787751

Setting the seed makes the sequence reproducible, but if that is not important,
you can leave it out. This assumes you want a normal distribution and you want
to specify the mean and standard deviation. If you want those to be selected
randomly. The following does that using uniform distributions so each mean and
standard deviation is equally likely within the range:
> x2 <- round(rnorm(20000, runif(1, 4, 6), runif(1, 2, 3)), 6)
> head(x2)
[1] 4.054289 4.745569 5.795536 6.316750 4.370713 5.586646

-------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77840-4352




-----Original Message-----
From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Adrian
Johnson
Sent: Tuesday, August 2, 2016 1:57 PM
To: r-help
Subject: [R] generate a vector of random numbers within confines of certain
parameters

Dear group,

I am trying to generate a vector of random numbers for 20K observation.

however, I want to generate numbers (with 6 decimal places) within the range of
Std. Dev : 2-3
mean  : 4-6

Is there a method to generate numbers with 6 decimal places under
these parameters

thank you.
Adrian

______________________________________________
R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

The second one (x2) uses the same mean/sd for the 20000 variates. If you want to
change the mean/sd for each variate:
> x3 <- round(replicate(20000, rnorm(1, runif(1, 4, 6), runif(1, 2, 3))),
6)
> head(x3)
[1] 5.648530 5.689563 2.945512 3.915723 8.527447 0.298535

-------
David C

-----Original Message-----
From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of David L
Carlson
Sent: Tuesday, August 2, 2016 2:40 PM
To: Adrian Johnson; r-help
Subject: Re: [R] generate a vector of random numbers within confines of certain
parameters

Try
> set.seed(42)
> x1 <- round(rnorm(20000, 4, 2), 6)
> head(x1)
[1] 6.741917 2.870604 4.726257 5.265725 4.808537 3.787751

Setting the seed makes the sequence reproducible, but if that is not important,
you can leave it out. This assumes you want a normal distribution and you want
to specify the mean and standard deviation. If you want those to be selected
randomly. The following does that using uniform distributions so each mean and
standard deviation is equally likely within the range:
> x2 <- round(rnorm(20000, runif(1, 4, 6), runif(1, 2, 3)), 6)
> head(x2)
[1] 4.054289 4.745569 5.795536 6.316750 4.370713 5.586646

-------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77840-4352




-----Original Message-----
From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Adrian
Johnson
Sent: Tuesday, August 2, 2016 1:57 PM
To: r-help
Subject: [R] generate a vector of random numbers within confines of certain
parameters

Dear group,

I am trying to generate a vector of random numbers for 20K observation.

however, I want to generate numbers (with 6 decimal places) within the range of
Std. Dev : 2-3
mean  : 4-6

Is there a method to generate numbers with 6 decimal places under
these parameters

thank you.
Adrian

______________________________________________
R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

______________________________________________
R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

x <- rnorm( 20000, 5, 2.5 )

The requirement for "random" is ill-specified because it omits mention
of which random distribution you want (I assumed normal distribution above).

The requirement for "decimal places" is ill-defined because floating
point numbers are internally represented with mantissa and exponent
("scientific notation"), so large numbers have fewer significant
"decimal places" in the fraction than small numbers do. For most
purposes double precision IEEE754 numbers have more precision than you will
need. What gets sticky is if you want to LIMIT the number of decimals... you may
need to use the sprintf function and export the data as character values if that
is important (which I doubt).

Note that the default behavior of the R console is to PRINT values with four
decimals, but the rest of the significant digits are really still there.
-- 
Sent from my phone. Please excuse my brevity.

On August 2, 2016 11:56:35 AM PDT, Adrian Johnson <oriolebaltimore at
gmail.com> wrote:
>Dear group,
>
>I am trying to generate a vector of random numbers for 20K observation.
>
>however, I want to generate numbers (with 6 decimal places) within the
>range of
>Std. Dev : 2-3
>mean  : 4-6
>
>Is there a method to generate numbers with 6 decimal places under
>these parameters
>
>thank you.
>Adrian
>
>______________________________________________
>R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.

All floating point operations are done to machine precision -- roughly
16 digits. See ?.Machine . You can choose to round, truncate, or
display to anything less than that that you care to. See also the
digits parameter of  ?options

The rest of your post is ambiguous to me. But note that (all?/most?)
rng's are vectorized, so e.g.
> set.seed(1123)
> rnorm(10,mean= runif(10,2,3), sd = runif(10,4,6))
 [1]  4.369411  1.944876  3.143913  6.489048 -1.093468  1.330675
-3.936239 11.740755
 [9] -2.260413 -1.748759

... if that's what you meant.

Cheers,
Bert


Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Tue, Aug 2, 2016 at 11:56 AM, Adrian Johnson
<oriolebaltimore at gmail.com> wrote:
> Dear group,
>
> I am trying to generate a vector of random numbers for 20K observation.
>
> however, I want to generate numbers (with 6 decimal places) within the
range of
> Std. Dev : 2-3
> mean  : 4-6
>
> Is there a method to generate numbers with 6 decimal places under
> these parameters
>
> thank you.
> Adrian
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.