R: How get the labels of attributes in a list-CodePudding

I have a data frame with labeled columns meaning I have both column names and one label for each column. The following code creates an analogous data frame:

data(mtcars)
mtcars = apply_labels(mtcars,
                      mpg = "Miles/(US) gallon",
                      cyl = "Number of cylinders",
                      disc = "Displacement (cu. in.)",
                      hp = "Gross horsepower",
                      drat = "Rear axle ratio",
                      wt = "weight (1000 lbs)",
                      qsec = "1/4 mile time",
                      vs = "Engine",
                      am = "Transmission"
                      gear = "Number of forward gears"
                      carb = "Number of carburetors"

My goal is to select columns by their labels ("Miles/(US) gallon", etc.). Does anyone know how to get access to those or know a function returning those labels?

Thank you very much for your help.

CodePudding user response：

I assume you are using the expss package to apply the labels. This package also contains the function var_lab which returns the label of any column. You can get a vector of labels using sapply(mtcars, var_lab). Then you can use this vector to subset the columns you need from the data frame.

library(expss)
data(mtcars)

mtcars = apply_labels(mtcars,
                      mpg = "Miles/(US) gallon",
                      cyl = "Number of cylinders",
                      disp = "Displacement (cu. in.)",
                      hp = "Gross horsepower",
                      drat = "Rear axle ratio",
                      wt = "weight (1000 lbs)",
                      qsec = "1/4 mile time",
                      vs = "Engine",
                      am = "Transmission",
                      gear = "Number of forward gears",
                      carb = "Number of carburetors")


labs <- sapply(mtcars,var_lab)

print(labs)
##                       mpg                       cyl                      disp 
##       "Miles/(US) gallon"     "Number of cylinders"  "Displacement (cu. in.)" 
##                        hp                      drat                        wt 
##        "Gross horsepower"         "Rear axle ratio"       "weight (1000 lbs)" 
##                      qsec                        vs                        am 
##           "1/4 mile time"                  "Engine"            "Transmission" 
##                      gear                      carb 
## "Number of forward gears"   "Number of carburetors"

subset <- mtcars[,labs %in% c('Number of cylinders','Gross horsepower')]

head(subset)
##                   cyl  hp
## Mazda RX4           6 110
## Mazda RX4 Wag       6 110
## Datsun 710          4  93
## Hornet 4 Drive      6 110
## Hornet Sportabout   8 175
## Valiant             6 105