R-将数据框中的变量转换为因子

Question

I have created a data frame from a SQL query using the RODBC package. I have a separate single column data frame in which each rows contains a name of a column in the main data set that I would like to convert to a factor.

This is the logic though the syntax is obviously wrong.

for(c in 1:length(df.ToFactor$IV)-0) {

 VarToFactor<- as.character(df.ToFactor$IV[c])
 df.dataset[VarToFactor]<-factor(df.HRV[VarToFactor])

}

Any help would be appreciated.

Answer 1

The subtraction of zero from a vector of integers doesn't make much sense. I suspect you may wnat to use the [[<var-name>]] construction:

for(c in 1:length(df.ToFactor$IV) ) {

 VarToFactor<- as.character(df.ToFactor[["IV"]][c])
 df.dataset[[VarToFactor]]<-factor(df.HRV[[VarToFactor]])
      }

I also changed the "$" operation to the equivalent "[[" operation just because it's safer in programming, although I think in a for-loop at an interactive session it would not cause problems. In addition to the ?Extract page where the detail of "[[" and "[" are described one can find useful information in the "R Inferno" by Patrick Burns. This particular area is covered on p 52.