Question

I am working on a large dataframe with >40 columns. I want to be able to move a column, without having to specify all the column names. For example:

a<-c(1:5)  
b<-c(4,3,2,1,1)  
Percent<-c(40,30,20,10,10)
Labels<-c("Cat","Dog","Rabbit","Rat","Mouse")
df1<-data.frame(a,b,Percent,Labels)

How would I move the column ‘Lables’ to before column ‘a’ WITHOUT having to write all the other column names (i.e. can I just specify a column to come before/after another column?).

Thanks.

Answer 1

Something quick and dirty would be (i.e. no sanity checking etc. and assuming only a single colname is supplied):

moveToFirstCol <- function(df, colname) {
    cnams <- colnames(df)
    want <- which(colname == cnams)
    df[, c(cnams[want], cnams[-want])]
}

which gives:

> moveToFirstCol(df1, "Labels")
  Labels a b Percent
1    Cat 1 4      40
2    Dog 2 3      30
3 Rabbit 3 2      20
4    Rat 4 1      10
5  Mouse 5 1      10

That should suggest a way to handle this sort of thing if you need additional flexibility.