how do I search for columns with same name, add the column values and replace these columns with same name by their sum? Using R

Question

I have a data frame where some consecutive columns have the same name. I need to search for these, add their values in for each row, drop one column and replace the other wi

Answer 1

Some sample data.

dfr <- data.frame(
  foo = rnorm(20),
  bar = 1:20,
  bar = runif(20),
  check.names = FALSE
)

Method: Loop over unique column names; if there is only one of that name, then selecting all columns with that nme will return a vector, but if there are duplicates it will also be a data frame. Use rowSums to sum over rows. (Duh. EDIT: Not quite as 'duh' as previously thought!) lapply returns a list, which we need to reform into a data frame, and finally we fix the names. EDIT: sapply avoids the need for the last step.

unique_col_names <- unique(colnames(dfr))
new_dfr <- sapply(unique_col_names, function(name)
{
  subs <- dfr[, colnames(dfr) == name]
  if(is.data.frame(subs))
    rowSums(subs)
  else
    subs
})