R help - Jan 2004 - how to overlap plots

Dear R experts:
Can you help me to overlap a histogram and theoretical density curve of poison 
distribution? for example data like this:
The numbers of sanils found in each of 100 sampling quadrats in an area were 
as follows:
number of snails, r 0 1  2 3 4 5 8 15
f=frequency of r   69 18 7 2 1 1 1 1
apparently this is not Poison but near to Poison, How to overlap the 
theoretical desity curve to the histgram of this data?
Thanks in advance!
Josh

< Can you help me to overlap a histogram and theoretical density curve of
poison distribution?>
There is more than one Poisson distribution you could possibly overlap but a
common choice is the Poisson with parameter = observed mean of the data - in
your case, 0.7.

I think the below is somewhat clumsy but it gives one idea how to do it (and
r-experts will cheerfully show a better way :)
> par(bg = "cornsilk")
> 
> #number of snails, 
> r <- c(0, 1, 2, 3, 4, 5, 8, 15)
> #frequency of r
> f <- c(69, 18, 7, 2, 1, 1, 1, 1)
> 
> #a clumsy way to bin the observed values
> breakz <- (0:16) - 0.5
> 
> x <- rep(r,f)
> 
> xbar <- mean(x)
> xbar
[1] 0.7
> 
> hist(x, breaks = breakz,
+ freq = FALSE,
+ font.main = 6, 
+         col = "lightgray")
> 
> #change lambda to change the Poisson dist
> points(x, dpois(x, lambda = xbar),
+         type = "l", col = 2)
>
bob


-----Original Message-----
From: szhan@uoguelph.ca [mailto:szhan@uoguelph.ca] 
Sent: Thursday, January 15, 2004 11:20 AM
To: r-help@stat.math.ethz.ch
Subject: [R] how to overlap plots

Dear R experts:
Can you help me to overlap a histogram and theoretical density curve of
poison 
distribution? for example data like this:
The numbers of sanils found in each of 100 sampling quadrats in an area were

as follows:
number of snails, r 0 1  2 3 4 5 8 15
f=frequency of r   69 18 7 2 1 1 1 1
apparently this is not Poison but near to Poison, How to overlap the 
theoretical desity curve to the histgram of this data?
Thanks in advance!
Josh

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> 
> Dear R experts:
> Can you help me to overlap a histogram and theoretical density curve of
poison
> distribution? for example data like this:
> The numbers of sanils found in each of 100 sampling quadrats in an area
were
> as follows:
> number of snails, r 0 1  2 3 4 5 8 15
> f=frequency of r   69 18 7 2 1 1 1 1
> apparently this is not Poison but near to Poison, How to overlap the 
> theoretical desity curve to the histgram of this data?
> Thanks in advance!
The fit.dist function in my gnlm library (www.luc.ac.be/~jlindsey/rcode.html)
does that automatically. Jim
> Josh
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>

Try the distplot() function in package vcd.

-Michael

-- 
Michael Friendly     Email: friendly at yorku.ca 
Professor, Psychology Dept.
York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
4700 Keele Street    http://www.math.yorku.ca/SCS/friendly.html
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