
Good Evening

Is there a setting that I can change in R so that I get either a warning or an error message if I reference  non-existent data in a data frame?  For example I get no warning or error message with the following:

> set.seed(2013)
> df0=data.frame(cbind(x=rnorm(1000),y=rnorm(1000)))
> df0$z=df0$w
> head(df0)
            x           y
1 -0.09202453  1.51179695
2  0.78901912 -0.60084547
3 -0.66744232 -0.02180077
4  1.36061149 -0.74909011
5  1.50768816 -2.25128946
6 -2.60754997  0.43708800

Thanks
Joe

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