On Wed, 30 Mar 2016, Erich Neuwirth wrote:
On 30 Mar 2016, at 02:53, Marine Regis <marine.re...@hotmail.fr> wrote:
Hello,
I would like to build a Lorenz curve and calculate a Gini coefficient in order
to find how much parasites does the top 20% most infected hosts support.
Here is my data set:
Number of parasites per host:
parasites = c(0,1,2,3,4,5,6,7,8,9,10)
Number of hosts associated with each number of parasites given above:
hosts = c(18,20,28,19,16,10,3,1,0,0,0)
To represent the Lorenz curve:
I manually calculated the cumulative percentage of parasites and hosts:
cumul_parasites <- cumsum(parasites)/max(cumsum(parasites))
cumul_hosts <- cumsum(hosts)/max(cumsum(hosts))
plot(cumul_hosts, cumul_parasites, type= "l?)
Your values in hosts are frequencies. So you need to calculate
cumul_hosts = cumsum(hosts)/sum(hosts)
cumul_parasites = cumsum(hosts*parasites)/sum(parasites)
That's what I thought as well but Marine explicitly said that the 'host'
are _not_ weights. Hence I was confused what this would actually mean.
Using the "ineq" package you can also do
plot(Lc(parasites, hosts))
The Lorenz curves starts at (0,0), so to draw it, you need to extend these
vectors
cumul_hosts = c(0,cumul_hosts)
cumul_parasites = c(0,cumul_parasites)
plot(cumul_hosts,cum9l_parasites,type=?l?)
The Gini coefficient can be calculated as
library(reldist)
gini(parasites,hosts)
If you want to check, you can ?recreate? the original data (number of parasited
for each host) with
num_parasites = rep(parasites,hosts)
and
gini(num_parasites)
will also give you the Gini coefficient you want.
From this Lorenz curve, how can I calculate the Gini coefficient with the function "gini"
in R (package reldist) given that the vector "hosts" is not a vector of weights ?
Thank you very much for your help.
Have a nice day
Marine
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