Reading numeric Date value from CSV file to data.frame in "R"

> D <- read.csv("sample1.csv", header = FALSE, sep = ",")

> D
        V1     V2     V3     V4
1 20100316 109825 352120 239065
2 20100317 108625 352020 239000
3 20100318 109125 352324 241065

> D[,1]
[1] 20100316 2开发者_如何学C0100317 20100318

In the above example how do I get the data in D[,1] to be read, and stored as date values: 2010-03-16, 2010-03-17, 2010-03-18? I have lots of data files in this format.

TIA,

dx = "20100316 20100317 20100318"    
# if your dates already exists as individual items of mode "character"
# then obviously, skip this step 
dx2 = unlist(strsplit(dx, split=" "))

fnx = function(x){as.Date(x, format="%Y%m%d")}

dx3 = fnx(dx2)
dx3
# returns: [1] "2010-03-16" "2010-03-17" "2010-03-18"

class(dx3)
# returns: [1] "Date"