Rename multiple dataframe columns, referenced by current names

Question

I want to rename some random columns of a large data frame and I want to use the current column names, not the indexes. Column indexes might change if I add

Answer 1

The trouble with changing column names of a data.frame is that, almost unbelievably, the entire data.frame is copied. Even when it's in .GlobalEnv and no other variable points to it.

The data.table package has a setnames() function which changes column names by reference without copying the whole dataset. data.table is different in that it doesn't copy-on-write, which can be very important for large datasets. (You did say your data set was large.). Simply provide the old and the new names:

require(data.table)
setnames(DT,"MyName.1", "MyNewName")
# or more explicit:
setnames(DT, old = "MyName.1", new = "MyNewName")
?setnames