[R] problem with as.Date

[Martin Spindler]

Dear all,

I would like to convert the first column of a dataframe to a date (original
format: year (4 digits) and month (last 2 digits))

>str(dat_FF)
'data.frame':	1022 obs. of  4 variables:
 $ date : int  192607 192608 192609 192610 192611 192612 192701 192702
192703 192704 ...
 $ Rm.Rf: num  2.69 2.52 0 -3.06 2.42 2.66 0 4.29 0.51 0.57 ...
 $ SMB  : num  -2.49 -1.25 -1.38 -0.2 -0.34 -0.07 -0.11 0.35 -1.87 0.44 ...
 $ HML  : num  -2.91 4.25 0.22 0.71 -0.4 -0.11 4.92 3.17 -2.92 1.33 ...

But

>dat_FF$date <- as.Date(as.character(dat_FF$date), format="%Y%m")

delievers NAs:

>str(dat_FF)
'data.frame':	1022 obs. of  4 variables:
 $ date : Date, format: NA NA ...

I am very grateful for hints! Thanks in advance!

Best,

Martin