[R] problems with simple statistical procedures

[Thomas Preuth]

Hello,

I use an imported dataframe and want to extract the mean value for one 
column.
after typing "mean (rae.df$VOL_DEP)" I receive
"[1] NA
Warning message:
Argument ist weder numerisch noch boolesch: gebe NA zurück in: 
mean.default("rae.df$POINT_Y_CH") "

But when i look into the dataframe the column is characterized as numeric.

Sorry for bothering but as a complete newbie I just cannot halp myself.

Greetings,
thomas