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rrlang

how to parse symbol's value instead of symbol' name


Q1:

sorting = function (table, column) {
  # mtcars[order(mpg),]
  return(table[order(column),])
}

sorting(mtcars, "mpg") is equivalent to mtcars[order("mpg"),] but not equals to the result I want to get which is mtcars[order(mpg),], how can I convert it from string to column name.

Q2:

similar:

library(tidyr)
comb = function(table, colNNN, arr, sep) {
  return(unite(table, colNNN, all_of(arr), sep = sep))
}

and I do

comb(mtcars,"gearCarb",c("gear","carb"), "-")

and I got colNNN as the final column name,

so how to convert symbol into a String?


Solution

  • Q1 can be solved without using non-standard evaluation using arrange_at from dplyr.

    library(dplyr)
    library(tidyr)
    library(rlang)
    
    sorting = function (table, column) {
       return(table %>% arrange_at(column))
    }
    
    sorting(mtcars, "mpg")
    
    #    mpg cyl  disp  hp drat    wt  qsec vs am gear carb
    #1  10.4   8 472.0 205 2.93 5.250 17.98  0  0    3    4
    #2  10.4   8 460.0 215 3.00 5.424 17.82  0  0    3    4
    #3  13.3   8 350.0 245 3.73 3.840 15.41  0  0    3    4
    #4  14.3   8 360.0 245 3.21 3.570 15.84  0  0    3    4
    #5  14.7   8 440.0 230 3.23 5.345 17.42  0  0    3    4
    #6  15.0   8 301.0 335 3.54 3.570 14.60  0  1    5    8
    #...
    

    For Q2 we can use {{}}

    comb = function(table, colNNN, arr, sep) {
      return(unite(table, {{colNNN}}, arr, sep = sep))
    }
    
    comb(mtcars,"gearCarb",c("gear","carb"), "-")
    
    #                     mpg cyl  disp  hp drat    wt  qsec vs am gearCarb
    #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
    #...