R

transformer <- function(df, col){

df1 <- df %>%select(cycling, col)

df1 <- df1[order(df1$col, decreasing = F),]

return (df1$col)
}
df1 <- transformer(df, 'dist_km')

df1 只有NULL

把df1$col改为df1[,2]即可

但为什么不能用df1$col呢