[R] concatenating columns in data.frame

[Micha Silver]

I need to create a new data.frame column as a concatenation of existing 
character columns. But the number and name of the columns to concatenate 
needs to be passed in dynamically. The code below does what I want, but 
seems very clumsy. Any suggestions how to improve?


df = data.frame("A"=sample(letters, 10), "B"=sample(letters, 10), 
"C"=sample(letters,10), "D"=sample(letters, 10))

# Which columns to concat:

use_columns = c("D", "B")


UpdateCombo = function(df, use_columns) {
     use_df = df[, use_columns]
     combo_list = lapply(1:nrow(use_df), function(r) {
     r_combo = paste(use_df[r,], collapse="_")
     return(data.frame("Combo" = r_combo))
     })
     combo = do.call(rbind, combo_list)

     names(combo) = "Combo"

     return(combo)

}


combo_col = UpdateCombo(df, use_columns)

df_combo = do.call(cbind, list(df, combo_col))


Thanks


-- 
Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918