[R] subtract a list of vectors from a list of data.frames in an elegant way

[Henrique Dallazuanna]

Try this:

mapply('[', DBquery, mapply(setdiff, lapply(DBquery, names), lookup))

On Sat, Mar 31, 2012 at 5:50 PM, Eric Fail <eric.fail at gmx.us> wrote:
> a working solution to the problem,
>
>  a <- DBquery[names(lookup)]
>
> mother.of.lookup <- list()
> for(string in names(a)) {
>   a[[string]] <- names(a[[string]])
>   mother.of.lookup[[string]] <- setdiff(a[[string]], lookup[[string]])
> }
>
> identical(mother.of.lookup, result)
>
> It might not be the most elegant solution, but it works.
>
> Best,
> Eric
>
> On Thu, Mar 29, 2012 at 4:07 AM, Jim Holtman <jholtman at gmail.com> wrote:
>>
>> ?setdiff
>>
>> Sent from my iPad
>>
>> On Mar 29, 2012, at 4:28, "Eric Fail" <eric.fail at gmx.us> wrote:
>>
>> > Dear R experts,
>> >
>> > I've realized that it might not be possible to define a negative SELCET statement in a SQL call so now I'm looking for the smoothest way to generate a list of what I would like from my large database by first pulling all the names with a query like this "SELECT top 1 * FROM your_table" (thank you Bart Joosen for the idea) and then subtract the variables I am not allow to pull manually ending up with a 'positive' definition of what I want, something I can use in a SQL SELCT statement (see my email on this list from yesterday for more on that).
>> >
>> > When I query the database for the variable names I get something similar to 'DBquery' in my working example below, but considerable longer with over 2400 hundred variables. As I only need to remove two or three variables I would like to define a lookup table (like the list 'lookup' in my example) and subtract that from my data base query. Now to my question. Is there a way I can subtract one list from another? Like setoff or alike?
>> >
>> > I would like to end up with a list like the one shown in my example called 'result.' In short, I would like to subtract 'lookup' from 'DBquery' and end up with 'result,' please note that 'result' is a list fo vecktors and not a list of dataframes. In my real life example DBquery is considerable longer so defining that by hand would make a really really long syntax.
>> >
>> > Hope someone know some smart function that I can use to solve my problem in an elegant way.
>> >
>> > Thanks for reading.
>> >
>> > Erick
>> >
>> > ###### begin R code ######
>> >
>> > DBquery     <- list(tableA=data.frame(id = numeric(0), atwin = numeric(0), atrout = numeric(0)),
>> >                    tableB=data.frame(id = numeric(0), mq   = numeric(0), z = numeric(0), m = numeric(0)),
>> >                    tableC=data.frame(V1 = numeric(0), mfn   = numeric(0), iiff = numeric(0)),
>> >                    tableD=data.frame(id    = numeric(0), msf   = numeric(0), oom  = numeric(0)))
>> >
>> > lookup     <- list(tableA=   c('atwin', 'atrout'),
>> >                   tableB=    c('m', 'z'),
>> >                   tableC=    'ALL')
>> >
>> > ### ...
>> >
>> > result     <- list(tableA= c('id'),
>> >                    tableB= c('id', 'mq'),
>> >                    tableC= c('V1', 'mfn', 'iiff'))
>> >
>> > ______________________________________________
>> > 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.
>
> ______________________________________________
> 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.



-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O