no_one no_one - 1 year ago 126
R Question

Fit poisson distribution to data (histogram + line)

I need to do exactly what @interstellar asked here Fit poisson distribution to data but within the R environment (not matlab).

So, I created a barplot with my observed values and I just need to fit a poisson distribution on it.

Here my data:

df = read.table(text = 'Var1 Freq
6 1
7 2
8 5
9 7
10 9
11 6
12 4
13 3
14 2
15 1', header = TRUE)

the barplot created is the following:

t = barplot(df$Freq, ylim = c(0,10))
axis(1, at=t, labels=df$Var1)

I am still new to R so how I could use the
function or something else to create a line above my barplot?

Any help would be really appreciated.


I have worked out something but I am not sure 100% if it is correct:

#create barplot
t = barplot(df$Freq, ylim = c(0,10))
axis(1, at=t, labels=df$Var1)

#find lambda value from my data
pois = fitdist(df$Freq, 'pois', method = 'mle')

Fitting of the distribution ' pois ' by maximum likelihood
estimate Std. Error
lambda 4 0.6324555

#create 10 values from a real poisson distribution
dist = dpois(1:10, lambda = 4)

#multiply them by `sum(df$Freq)` in order to scale them to the barplot
dist = dist * sum(df$Freq)

#add the line plot to the original barplot
lines(dist, lwd = 2)


However, the curve is not smooth..

Answer Source
 #fit poisson distr to tbl$Freq data
poisson = fitdist(df$Freq, 'pois', method = 'mle')

plot(df$Var1, df$Freq, type = 'h', ylim = c(0,10), ylab = 'No. of years with x events', 
     xlab = 'No. of events in a year', main = 'All 13-day events with Poisson')

dist = dpois(1:10, lambda = 4)
dist = dist * sum(df$Freq)
dist =
dist$Var1 = df$Var1

lines(dist$Var1, dist$dist, lwd = 2)
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