# [R] runif with weights

Bert Gunter gunter.berton at gene.com
Thu May 31 00:25:33 CEST 2007

```You did not explicitly say it, but your example indicates that you want to
sample from integers only (else what would weights mean?). So...

?sample  -- in particular note the prob argument and read help docs
carefully

e.g.

sample(100,25,prob=c(0,rep.int(.4,9),rep.int(.6,90))) ## without replacement

Bert Gunter
Genentech Nonclinical Statistics

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Ken Knoblauch
Sent: Wednesday, May 30, 2007 5:59 PM
To: Joao.Fadista at agrsci.dk
Cc: r-help at stat.math.ethz.ch
Subject: [R] runif with weights

Not sure why you have set the probability of a 1 to 0 but maybe something
like this might be what you want:

round( ifelse( rbinom(25, 1, 0.4), runif(25, 2, 10), runif(25, 11, 100) ) )
[1]  2  6 34 90 79 71 83  8 47 36 21 32 17 71  3 16  9 65 94  6 30  5  7
10 13

############
I would like to generate 25 numbers from 1 to 100 but I would like to have
some numbers that could  be more probable to come out. I was thinking of
the function runif:
runif(25, 1, 100) , but I don´t know how to give more weight to some
numbers.

Example:
each number from 2 to 10 has the probability of 40% to come out but the
probability of each number from 11 to 100 to come out is 60%.

--
Ken Knoblauch
Inserm U846
Institut Cellule Souche et Cerveau
Département Neurosciences Intégratives
18 avenue du Doyen Lépine
69500 Bron
France
tel: +33 (0)4 72 91 34 77
fax: +33 (0)4 72 91 34 61
portable: +33 (0)6 84 10 64 10
http://www.pizzerialesgemeaux.com/u846/

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