Calculated mean value based on another column bin from dataframe.

Dear list,

I have a dataframe with two column as fellow.

head(dat)

? ? ? V1 ? ? ?V2
?0.15624 0.94567
?0.26039 0.66442
?0.16629 0.97822
?0.23474 0.72079
?0.11037 0.83760
?0.14969 0.91312

I want to get the column V2 mean value based on the bin of column of
V1. I write the code as fellow. It works, but I think this is not the
elegant way. Any suggestions?

dat<-read.table("dat.txt",head=F)
ran<-seq(0,0.5,0.05)
mm<-NULL
for (i in c(1:(length(ran)-1)))
{
? ?fil<- dat[,1] > ran[i] & dat[,1]<=ran[i+1]
? ?m<-mean(dat[fil,2])
? ?mm<-c(mm,m)
}
mm

Here is the first 20 lines of my data.

dput(head(dat,20))

structure(list(V1 = c(0.15624, 0.26039, 0.16629, 0.23474, 0.11037,
0.14969, 0.16166, 0.09785, 0.36417, 0.08005, 0.29597, 0.14856,
0.17307, 0.36718, 0.11621, 0.23281, 0.10415, 0.1025, 0.04238,
0.13525), V2 = c(0.94567, 0.66442, 0.97822, 0.72079, 0.8376,
0.91312, 0.88463, 0.82432, 0.55582, 0.9429, 0.78956, 0.93424,
0.87692, 0.83996, 0.74552, 0.9779, 0.9958, 0.9783, 0.92523, 0.99022
)), .Names = c("V1", "V2"), row.names = c(NA, 20L), class = "data.frame")