[R] efficient ways to dynamically grow a dataframe

[Matteo Richiardi]

Hi,
I'm trying to write a small microsimulation in R: that is, I have a
dataframe with info on N individuals for the base-year and I have to
grow it dynamically for T periods:

df = data.frame(
 id = 1:N,
 x =....
)

The most straightforward way to solve the problem that came to my mind
is to create for every period a new dataframe:

for(t in 1:T){
 for(i in 1:N){
  row = data.frame(
   id = i,
   t = t,
   x = ...
   )
   df = rbind(df,row)
 }
}

This is very inefficient and my pc gets immediately stucked as N is
raised above some thousands.
As an alternative, I created an empty dataframe for all the projected
periods, and then filled it:

df1 = data.frame(
 id = rep(1:N,T),
 t = rep(1:T, each = N),
 x = rep(NA,N*T)
)

for(t in 1:T){
 for(i in 1:N){
  x = ...
  df1[df1$id==i & df1$t==t,"x"] = x
 }
}
df = rbind(df,df1)

This is also too slow, and my PC gets stucked. I don't want to go for
a matrix, because I'd loose the column names and everything will
become too much error-prone.
Any suggestions on how to do it?
Thanks in advance,
Matteo




-- 
Matteo Richiardi
University of Turin
Faculty of Law
Department of Economics "Cognetti De Martiis"
via Po 53, 10124 Torino
Email: matteo.richiardi at unito.it
Tel. +39 011 670 3870
Web page: http://www.personalweb.unito.it/matteo.richiardi/