[R] concatenating columns in data.frame

Micha Silver t@v|b@r @end|ng |rom gm@||@com
Thu Jul 1 16:36:06 CEST 2021

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"



combo_col = UpdateCombo(df, use_columns)

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


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

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