R help - May 2007 - runif with weights

Dear all,
 
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%.
 
 
 
Kind regards and thanks in advance,
Jo?o Fadista

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
D?partement Neurosciences Int?gratives
18 avenue du Doyen L?pine
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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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
D?partement Neurosciences Int?gratives
18 avenue du Doyen L?pine
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/