Efficiently adding or removing elements to a vector or list in R?

Question

I\'m implementing an algorithm that involves lots of adding and removing things from sets. In R, this is slow because as far as I know, adding or removing things from a vect

Answer 1

If you can, initializing a vector so that it has length equal to its maximum length during the algorithm may help.

e.g.

vec <- rep(NA,10)
vec[1:3] <- 1:3
vec[4:5] <- 4:5
vec[6:10] <- 6:10

rather than

vec <- 1:3
vec <- c(vec,4:5)
vec <- c(vec,6:10)

compare

> system.time({vec <- rep(NA,10^4); for (i in 1:(10^4)) vec[i] <- i })
   user  system elapsed 
  0.043   0.001   0.044 

to

> system.time({vec <- NULL; for (i in 1:(10^4)) vec <- c(vec,i) })
   user  system elapsed 
  0.249   0.089   0.335