7.1 mutate & transmute

mutate allows to create new columns that are functions of the existing ones.

• Create a new column with the duration of each term:

# Subtracting column start to column end
mutate(presidential, 
    duration_days=end-start)

Notes:

• Use unquoted column names.
• Columns are added at the end of the data frame.
• mutate keeps all columns.

You can change where the column is added (if you don’t want it to be added at the last position):

# add it before column "start"
mutate(presidential, 
    duration_days=end-start,
    .before=start)

# add it after column "end"
mutate(presidential, 
    duration_days=end-start,
    .after=end)

If you want to keep only the newly created column(s) (drop the remaining ones): use transmute() instead of mutate():

transmute(presidential, 
    duration_days=end - start)

Re-assign to a new - or the same - data frame/tibble using the usual R assignment operator: <-

presidential2 <- mutate(presidential, 
                duration_days=end - start)

• If you want to change the name of a column, you can use the function rename:

# using the column name:
rename(presidential2, 
       President=name)

# or the column index:
rename(presidential2, 
       President=1)

# you can rename several columns using the same command:
rename(presidential2, 
       President=name, 
       Political_party=party)