[R] Matrix oriented computing

[Marc Schwartz]

On Fri, 2005-08-26 at 14:44 +0200, Sigbert Klinke wrote:
> Hi,
> 
> I want to compute the quantiles of Chi^2 distributions with different 
> degrees of freedom like
> 
> x<-cbind(0.005, 0.010, 0.025, 0.05, 0.1, 0.5, 0.9, 0.95, 0.975, 0.99, 0.995)
> df<-rbind(1:100)
> m<-qchisq(x,df)
> 
> and hoped to get back  a  length(df) times length(x)  matrix with the 
> quantiles. Since this does not work, I use
> 
> x<-c(0.005, 0.010, 0.025, 0.05, 0.1, 0.5, 0.9, 0.95, 0.975, 0.99, 0.995)
> df<-c(1:100)
> m<-qchisq(x,df[1])
> for (i in 2:length(df)) {
>   m<-rbind(m,qchisq(x,df[i]))
> }
> dim(m)<-c(length(df),length(x))
> 
> Is there a way to avoid the for loop ?
> 
> Thanks Sigbert

See ?sapply

x <- c(0.005, 0.010, 0.025, 0.05, 0.1, 0.5, 0.9, 
       0.95, 0.975, 0.99, 0.995)

df <- c(1:100)

mat <- sapply(x, qchisq, df)

> dim(mat)
[1] 100  11
 
> str(mat)
 num [1:100, 1:11] 3.93e-05 1.00e-02 7.17e-02 2.07e-01 4.12e-01 ...


HTH,

Marc Schwartz