[R] Recoding Multiple Variables in a Data Frame in One Step

[David Winsemius]

On Jul 21, 2011, at 8:06 PM, Anthony Damico wrote:

> Hi, I can't for the life of me find how to do this in base R, but  
> I'd be
> surprised if it's not possible.
>
> I'm just trying to replace multiple columns at once in a data frame.
>
> #load example data
> data(api)
>
> #this displays the three columns and eight rows i'd like to replace
> apiclus1[ apiclus1$meals > 98 , c( "pcttest" , "api00" ,  
> "sch.wide" ) ]
>
>
> #the goal is to replace pcttest with 100, api100 with NA, and  
> sch.wide with
> "Maybe"
>
> #this doesn't work--
> apiclus1[ apiclus1$meals > 98 , c( "pcttest" , "api00" ,  
> "sch.wide" ) ] <-
> c( 100 , NA , "Maybe" )
>
> #the results replace downward instead of across
> apiclus1[ apiclus1$meals > 98 , c( "pcttest" , "api00" ,  
> "sch.wide" ) ]

If I had noted that I would have tried this:

apiclus1[ apiclus1$meals > 98 , rep( c( "pcttest" , "api00" ,  
"sch.wide" ),
                                        each =  sum(apiclus1$meals > 98)
                                     ) ]

Should be pretty easy to test, but since _you_ are the one responsible  
for providing examples for testing when posting to rhelp,  I am going  
to throw an untested theory back at you.


>
> I know I can do this with a few more steps (like one variable at a  
> time or
> by counting the number of rows to replace and then using rep() ..but  
> I'm
> hoping there's a quicker way?
>
>
> Thanks!!
>
> Anthony Damico


David Winsemius, MD
West Hartford, CT