Comparison of efficiency methods to concatenate data (list, vector and data.frame)

As you can see, the use of c() to concatenate data into an object is not very efficient. It is better to create an object of the final size and replace data. However, there are no difference if the list element is replaced or the content of the list element:

For vector:

> c <- NULL
> system.time(
+ for (i in 1:100000) c <- c(c, rnorm(1, 1, 1))
+ )
utilisateur     système      écoulé 
     26.971       8.214      35.681 

> c <- rep(NA, 100000)
> system.time(
+ for (i in 1:100000) c[i] <- rnorm(1, 1, 1)
+ )
utilisateur     système      écoulé 
      0.479       0.045       0.525 

For list:

> library(embryogrowth)
> 
> c <- list()
> system.time(
+ for (i in 1:100000) c <- c(c, list(resultNest_4p))
+ )
utilisateur     système      écoulé 
     68.412       7.460      76.696 
> 
> c <- rep(list(), 100000)
> system.time(
+   for (i in 1:100000) c[i] <- list(resultNest_4p)
+ )
utilisateur     système      écoulé 
     44.764       6.975      51.899 
> 
> c <- rep(list(), 100000)
> system.time(
+   for (i in 1:100000) c[[i]] <- resultNest_4p
+ )
utilisateur     système      écoulé 
     44.902       6.975      51.996 

For data.frame

> system.time({
+   df <- data.frame(col1=numeric(), col2=character(), stringsAsFactors = FALSE);
+   
+   for (i in 1:10000) {
+     df <- rbind(df, data.frame(col1=i, col2=as.character(i)))
+   }
+ }
+ )
utilisateur     système      écoulé 
     29.227       1.607      30.886 
> system.time({
+   df <- data.frame(col1=rep(NA, 10000), col2=rep(NA, 10000), stringsAsFactors = FALSE);
+   
+   for (i in 1:10000) {
+     df[i, "col1"] <- i
+     df[i, "col2"]  <- as.character(i)
+   }
+ }
+ )
utilisateur     système      écoulé 
      1.822       0.253       2.080 

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