How to dplyr rename a column by column index?

Question

The following code renames the first column in the dataset:

require(dplyr)    
mtcars %>%
        setNames(c("RenamedColumn", names(.)[2:length(names(.))]))

Desired Results:

                    RenamedColumn cyl  disp  hp drat    wt  qsec vs am gear carb
Mazda RX4                    21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
Mazda RX4 Wag                21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
Datsun 710                   22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1

Is it possible to get the same result using the column index? rename

It:

mtcars %>%
    rename(1 = "ChangedNameAgain")

will fail:

Error in source("~/.active-rstudio-document", echo = TRUE) : 
  ~/.active-rstudio-document:7:14: unexpected '='
6: mtcars %>%
7:     rename(1 =
                ^

Similarly, trying to use rename_or .[[1]]as a column reference returns an error.

Answer 1

Logic rename()is equal new_name = old_name, so it ChangedNameAgain = 1will make more sense than 1 = ChangedNameAgain.

I would suggest:

mtcars %>% rename_(ChangedNameAgain = names(.)[1])
#                     ChangedNameAgain cyl  disp  hp drat    wt  qsec vs am gear carb
# Mazda RX4                       21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
# Mazda RX4 Wag                   21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
# Datsun 710                      22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1
# Hornet 4 Drive                  21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1
# Hornet Sportabout               18.7   8 360.0 175 3.15 3.440 17.02  0  0    3    2
# Valiant                         18.1   6 225.0 105 2.76 3.460 20.22  1  0    3    1

Edit

dplyr rlang, 0.6/0.7 dplyr.

rename, , , @jzadra , "foo bar".

rlang. , , :

df <- tibble("foo" = 1:2, "bar baz" = letters[1:2])

# # A tibble: 2 x 2
#     foo `bar baz`
#   <int>     <chr>
# 1     1         a
# 2     2         b

rename(), , , . , FIXME ( FIXME ?) ( dplyr 0.7.4), :

df %>% rename(qux = !! quo(names(.)[[2]]))

# Error: Expressions are currently not supported in `rename()`

select, . , rename:

df %>% select(qux = !! quo(names(.)[[2]]), everything())

# # A tibble: 2 x 2
#     qux   foo
#   <chr> <int>
# 1     a     1
# 2     b     2

, :=, . , , " " ( vignette) enquo() quo_name() ( , , ):

rename_col_by_position <- function(df, position, new_name) {
  new_name <- enquo(new_name)
  new_name <- quo_name(new_name)
  select(df, !! new_name := !! quo(names(df)[[position]]), everything())
}

:

rename_col_by_position(df, 2, "qux")

# # A tibble: 2 x 2
#     qux   foo
#   <chr> <int>
# 1     a     1
# 2     b     2

quosure:

rename_col_by_position(df, 2, quo(qux))

# # A tibble: 2 x 2
#     qux   foo
#   <chr> <int>
# 1     a     1
# 2     b     2

:

rename_col_by_position(df, 2, qux)

# # A tibble: 2 x 2
#     qux   foo
#   <chr> <int>
# 1     a     1
# 2     b     2

:

rename_col_by_position(df, 2, `qux quux`)

# # A tibble: 2 x 2
#   `qux quux`   foo
#        <chr> <int>
# 1          a     1
# 2          b     2

Answer 2

, , , , .. select , , ,

mtcars %>% select( RenamedColumn = 1, everything() )

select , , . , , :

## This will rename the 7th column without changing column order
mtcars %>% select( 1:6, RenamedColumn = 7, everything() )

- rename_at, :

## This will also rename the 7th column without changing the order
## Credit for simplifying the second argument: Moody_Mudskipper
mtcars %>% rename_at( 7, ~"RenamedColumn" )

~, rename_at . , mtcars %>% rename_at( c(2,4), toupper ) .

Answer 3

Imho rlang, as @Aurele suggests, is too much here.

Solution 1: Use the pipe bracket context:

bcMatrix %>% {colnames(.)[1] = "foo"; .}

Solution 2: Or (ab) use the tee operator %>%from the package magrittr(installed in any case, if used dplyr) to perform renaming as a side effect:

bcMatrix %T>% {colnames(.)[1] = "foo"}

Solution 3: using a simple helper function:

rename_by_pos = function(df, index, new_name){ 
    colnames(df)[index] = new_name 
    df 
}
iris %>% rename_by_pos(2,"foo")