Speed to extract vector element by name with or without returning name: ["x"], [["x"]], [n] or unname()

The speed is higher using [[n]] then [["x"]]. unname(["x"]) is the slowest. 

> Growth
       alpha         beta            M            S            K           x0 
 0.007984356  0.018129643 81.782205061  2.978223538 13.309442413  5.072000000 

> system.time({for(i in 1:1E6) K <- Growth[[1]]})
   user  system elapsed 
  0.035   0.000   0.035 
> system.time({for(i in 1:1E6) K <- Growth[["alpha"]]})
   user  system elapsed 
  0.083   0.002   0.086 
> system.time({for(i in 1:1E6) K <- Growth[1]})
   user  system elapsed 
  0.145   0.004   0.150 
> system.time({for(i in 1:1E6) K <- Growth["alpha"]})
   user  system elapsed 
  0.150   0.004   0.154 
> system.time({for(i in 1:1E6) K <- unname(Growth[1])})
   user  system elapsed 
  1.122   0.007   1.135 
> system.time({for(i in 1:1E6) K <- unname(Growth["alpha"])})
   user  system elapsed 
  1.144   0.011   1.158 

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