David
>
> 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
>
> "A big computer, a complex algorithm and a long time does not equal
> science."
>
> -Robert Gentleman
>
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David Winsemius
Alameda, CA, USA