Extending Suffixes in Merge to All Non-by Columns

Question

suffixes in merge works only on common column names. Is there anyway to extend this to the rest of the columns as well without manually updating co

Answer 1

Try the following:

colnames(
  mergeWithSuffix(df1,df2, by = 'a', suffixes = c("1","2"))
)
[1] "a"   "b.1" "d.1" "d.2"

Notice that the original data.frames are unharmed.

colnames(df1)
[1] "a" "b" "d"

colnames(df2)
[1] "a" "d"

The functions are as follows

require(data.table)

mergeWithSuffix <- function(x, y, by, suffixes=NULL, ...) {

  # Add Suffixes
  mkSuffix(x, suffixes[[1]], merge.col=by)
  mkSuffix(y, suffixes[[2]], merge.col=by)

  # Merge
  ret <- merge(x, y, by = by, suffixes = NULL, ...)

  # Remove Suffixes
  undoSuffix(x, suffixes[[1]], merge.col=by)
  undoSuffix(y, suffixes[[2]], merge.col=by)
  return(ret)
}

mkSuffix <- function(x, sfx, sep=".", merge.col=NULL)  {
  nms <- setdiff(names(x), merge.col)
  setnames(x, nms, paste(nms, sfx, sep=".") ) 
}

undoSuffix <- function(x, sfx, sep=".", merge.col=NULL) {
  nms <- setdiff(names(x), merge.col)
  setnames(x, nms, sub(paste0(get("sep"), sfx, "$"), "", nms))
}

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Notice that setnames works by reference, so the overhead is almost negligible. Also, as discussed elsewhere, this works equally well on data.frames and data.table