Q: mutate_at for column-names that include a space Having a data.frame (tibble) as follows:
require(dplyr)
df_org <- df <- data_frame(a=1:2, b=c("A", "B"))
colnames(df) <- paste("X", c("Y", "Z"))

# A tibble: 2 × 2
  `X Y` `X Z`
  <int> <chr>
1     1     A
2     2     B

Using mutate_at throws the following error:
df_org %>% mutate_at(1, sum) # Works as expected
df %>% mutate_at(1, sum) # Error


Error in parse(text = x) : :1:3: unexpected symbol
  1: X Y
  --------^

Is this a bug? Am i doing anything wrong?
P.S.:
I am using dplyr 0.5.0 on OS X El Capitan 10.11.6

A: If you use vars for selecting the columns things work as expected.  I'm not sure if needing to use vars like this is expected or not.
df %>% mutate_at(vars(1), sum)

# A tibble: 2 x 2
    X Y   X Z
  <int> <chr>
1     3     A
2     3     B

