[R] Make sure a data frame has been "fun through" a function

[stephen sefick]

Hello All,

I am writing a package. I would like to encourage the user to look at the
data to rectify errors with function A before utilizing function B to code
these data as binary. I thought about solving this problem by adding a
"flag" in the attributes that could be used downstream in B, and have a
function that adds this "flag" if the user is convinced that everything is
okay. This would allow the user to utilize their data as is, if error
checking is not necessary. Maybe I am overthinking this. Thanks again.
kindest regards,

Stephen

On Mon, Feb 20, 2017 at 6:24 PM, Charles C. Berry <ccberry at ucsd.edu> wrote:

> On Mon, 20 Feb 2017, stephen sefick wrote:
>
> Hello,
>>
>> I would like to add something to a data frame that is 1) invisible to the
>> user, 2) has no side effects, and 3) I can test for in a following
>> function. Is this possible? I am exploring classes and attributes and I
>> have thought about using a list (but 1 and 2 not satisfied). Any help
>> would
>> be greatly appreciated.
>>
>>
> Depends on exactly what you mean by `invisible' and `side effects'.
>
> You can do this (but I am not necessarily recommending this):
>
> add.stuff <- function(x,...){
>>
> + class(x)<- c("more.stuff",class(x))
> + attr(x,"stuff")<- list(...)
> + x}
>
>>
>>
> And printing and model functions will be unaffected:
>
> df <- data.frame(a=1:3,b=letters[1:3])
>> df2 <- add.stuff(df,comment="wow", length="3 rows")
>> df2
>>
>   a b
> 1 1 a
> 2 2 b
> 3 3 c
>
>> attr(df2,"stuff")
>>
> $comment
> [1] "wow"
>
> $length
> [1] "3 rows"
>
> all.equal(lm(a~b,df),lm(a~b,df2)) # only call should differ
>>
> [1] "Component “call”: target, current do not match when deparsed"
>
>>
>>
> And if you need some generics to take account of the "stuff" attribute,
> you can write the methods to do that.
>
> ---
>
> Another solution is to put your data.framne in a package and then have
> other objects hold the 'stuff' stuff. Once your package is loaded or
> imported, the user will have access to the data in a way that might be said
> to be `invisible' in ordinary usage.
>
> ---
>
> But seriously, you should say *why* you want to do this. There are
> probably excellent solutions that do not involve directly altering the
> data.frame and may not involve putting together a package.
>
> HTH,
>
> Chuck




-- 
Let's not spend our time and resources thinking about things that are so
little or so large that all they really do for us is puff us up and make us
feel like gods.  We are mammals, and have not exhausted the annoying little
problems of being mammals.

                                -K. Mullis

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                              -Robert Gentleman

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