In dplyr, how to delete and rename columns that don't exist, manipulate all names, and name a new variable using a string?

Question

How can I simplify or perform the following operations using dplyr:

1. Run a function on all data.frame names, like mutate_each(funs()) for values, e.g.

   names(iris) <- make.names(names(iris))
   

2. Delete columns that do NOT exist (i.e. delete nothing), e.g.

   iris %>% select(-matches("Width")) # ok
   iris %>% select(-matches("X"))     # returns empty data.frame, why?
   

3. Add a new column by name (string), e.g.

   iris %>% mutate_("newcol" = 0) # ok
   
   x <- "newcol"
   iris %>% mutate_(x = 0) # adds a column with name "x" instead of "newcol"
   

4. Rename a data.frame colname that does not exist

   names(iris)[names(iris)=="X"] <- "Y"
   
   iris %>% rename(sl=Sepal.Length) # ok
   iris %>% rename(Y=X)             # error, instead of no change
   

Answer 1

Answer for the question n.2:

You can use the function any_of if you want to give explicitly the full names of the columns.

iris %>% 
    select(-any_of(c("X", "Sepal.Width","Petal.Width")))

This will not remove the non-existing column X and will remove the other two listed.

Otherwise, you are good with the solution with matches or a combination of any_of and matches.

  iris %>% 
    select(-any_of("X")) %>% 
    select(-matches("Width"))

This will remove explicitly X and the matches. Multiple matches are also possible.

iris %>% 
    select(-any_of("X")) %>%
    select(-matches(c("Width", "Spec"))) # use c for multiple matches