R/is.pois.R

In DnE: Distribution and Equation

is.pois <-
function(x,a=10,lambda=NULL)
{
	re=1;
	for(i in 1:length(x))
		if(x[i]<0||round(x[i])!=x[i])
			re=-1;
	di=max(x)-min(x)+1;
	p=rep(0,di+1);
	y=rep(0,di+1);
	q=0;
	if(re==-1)
	{
		return(data.frame("state"=-1,"pvalue"=1));
	}
	else
	{
		if(is.null(lambda))
		{
			lambda=mean(x);
			df=di-1;
		}
		else
		{
			df=di;
		}
		if(lambda>=0)
		{
			for(i in 1:di)
			{
				p[i]=dpois(min(x)+i-1,lambda);
			if(p[i]==0)
			{
				break;
			}
				for(j in 1:length(x))
				if(x[j]==min(x)+i-1)
					y[i]=y[i]+1;
			q=q+(y[i]-(length(x)*p[i]))^2/(length(x)*p[i]);
			}
		p[di+1]=1-ppois(max(x),lambda);
		q=q+length(x)*p[di+1];
		q0=qchisq(1-a,df);
                pvalue=pchisq(q,df);
		if(q<=q0)
		{
			return(data.frame("qchisq"=q,"pvalue"=pvalue));
		}
		else
		{
			return(data.frame("state"=-1,"pvalue"=1));
		}
		}
		else 
		{
			return(data.frame("state"=-1,"pvalue"=1));
		}
	}
}