[R] lapply to change variable names and variable values

[R. Michael Weylandt]

Your function doesn't return the new data frame but rather the new
names. Note, e.g.

x <- 1:2
names(x) <- letters[1:2]
.Last.value # Not x!

Try this:

.xx<- lapply(.xx, function(x) {colnames(x)<-c('State', 'Year');  x})

or more explicitly

.xx<- lapply(.xx, function(x) {colnames(x)<-c('State', 'Year');  return(x)})

Michael

On Mon, Mar 12, 2012 at 2:37 PM, Simon Kiss <sjkiss at gmail.com> wrote:
> Hi: I'm sure this is a very easy problem. I've consulted Data Manipulation With R and the R Book and can't find an answer.
>
> Sample list of data frames looks as follows:
>
> .xx<-list(df<-data.frame(Var1=rep('Alabama', 400), Var2=rep(c(2004, 2005, 2006, 2007), 400)), df2<-data.frame(Var1=rep('Tennessee', 400), Var2=rep(c(2004,2005,2006,2007), 400)), df3<-data.frame(Var1=rep('Alaska', 400), Var2=rep(c(2004,2005,2006,2007), 400)) )
>
> I would like to accomplish the following two tasks.
> First, I'd like to go through and change the names of each of the data frames within the list
> to be 'State' and 'Year'
>
> Second, I'd like to go through and add one year to each of the 'Var2'  variables.
>
> Third, I'd like to then delete those cases in the data frames that have values of Var2 (or Year) values of 2008.
>
> I could do this manually, but my data are actually bigger than this, plus I'd really like to learn. I've been trying to use lapply, but I can't get my head around how it works:
>  .xx<- lapply(.xx, function(x) colnames(x)<-c('State', 'Year')
> just changes the actual list of data frames to a list of the character string ('State' and 'Year')  How do I actually change the underlying variable names?
>
> I'm grateful for your suggestions!
> Simon Kiss
>
> *********************************
> Simon J. Kiss, PhD
> Assistant Professor, Wilfrid Laurier University
> 73 George Street
> Brantford, Ontario, Canada
> N3T 2C9
> Cell: +1 905 746 7606
>
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