dplyr NSE：将数据框中的多列居中

Question

I am trying to "center" multiple columns in a dataframe using dplyr but I keep getting a "non-numeric argument to binary operator" evaluation error. I think it is because I am trying to pass a string in when my function expects a bare variable name. However, using the syms() function does not help.

center <- function(var) {
  var <- enquo(var)
  var_ctrd <- paste0(quo_name(var), "_ctrd")
  dataset <- dataset %>% 
    group_by(Gender) %>% 
    mutate(!! var_ctrd := !! var - mean(!! var, na.rm = TRUE))
}

# Pull out character vector of modifier names
mod_names <- dataset %>% 
  select(NeckLengthCm:FlexExtDiff_Peak_abs) %>% 
  colnames()

# Iterate over modifiers
walk(syms(mod_names), center)

Does anyone know how to solve this or if there is a better solution?

Answer 1

You can use mutate_at() to center a subset of variables using a vector of variable names

# Only center a subset
vars <- colnames(mtcars)[1:4]

mtcars %>% 
  mutate_at(vars, scale, scale = FALSE)

Answer 2

I have another suggestion within the mutate_at :

mtcars %>% 
  mutate_at(.vars = colnames(mtcars)[1:4], 
            .funs = list("scaled" = scale))

Here you get exactly what you wanted. Scaled variables in new columns with suffix.

   mpg cyl disp  hp drat    wt  qsec vs am gear carb mpg_scaled cyl_scaled disp_scaled  hp_scaled
1 21.0   6  160 110 3.90 2.620 16.46  0  1    4    4  0.1508848 -0.1049878 -0.57061982 -0.5350928
2 21.0   6  160 110 3.90 2.875 17.02  0  1    4    4  0.1508848 -0.1049878 -0.57061982 -0.5350928
3 22.8   4  108  93 3.85 2.320 18.61  1  1    4    1  0.4495434 -1.2248578 -0.99018209 -0.7830405
4 21.4   6  258 110 3.08 3.215 19.44  1  0    3    1  0.2172534 -0.1049878  0.22009369 -0.5350928
5 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2 -0.2307345  1.0148821  1.04308123  0.4129422
6 18.1   6  225 105 2.76 3.460 20.22  1  0    3    1 -0.3302874 -0.1049878 -0.04616698 -0.6080186