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

[William Dunlap]

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of David Winsemius
> Sent: Monday, July 25, 2011 3:39 PM
> To: Anthony Damico
> Cc: r-help at r-project.org
> Subject: Re: [R] Recoding Multiple Variables in a Data Frame in One Step
> 
> 
> 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" )

Try list(pcttest=100, api00=NA, sch.wide="Maybe") instead
of c(100, NA, "Maybe") as the new value.

Here is a self-contained example
 > df <- data.frame(Size=sin(1:10), Name=state.name[11:20], Value=11:20, stringsAsFactors=FALSE)
 > df[df$Size<0, c("Name", "Value")] <- list(Name="JUNK", Value=-99)
 > df
          Size      Name Value
 1   0.8414710    Hawaii    11
 2   0.9092974     Idaho    12
 3   0.1411200  Illinois    13
 4  -0.7568025      JUNK   -99
 5  -0.9589243      JUNK   -99
 6  -0.2794155      JUNK   -99
 7   0.6569866  Kentucky    17
 8   0.9893582 Louisiana    18
 9   0.4121185     Maine    19
 10 -0.5440211      JUNK   -99

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com 

> >
> > #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
> 
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