[R] Errors or warnings for non-existent data

[Prof Brian Ripley]

On 16/03/2013 07:19, brwin338 wrote:
>
> 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:

Use specific methods of indexing as a data frame: [ not $.  That $ 
returns NULL for a non-existent list component is deliberate design, and 
as the help says

      Note that there is no ‘data.frame’ method for ‘$’, so ‘x$name’
      uses the default method which treats ‘x’ as a list.  There is a
      replacement method which checks ‘value’ for the correct number of
      rows, and replicates it if necessary.

E.g.

 > df0["w"]
Error in `[.data.frame`(df0, "w") : undefined columns selected

Other bad habits to get out of are not using your space bar, and using = 
for assignment in public code: your second line is very hard for humans 
to parse compared to

df0 <- data.frame(x = rnorm(1000), y = rnorm(1000))

the cbind() being a waste of time (it forms a matrix and data.frame then 
splits it up into columns).


>> 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
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595