writing to a dataframe from a for-loop in R

Question

I\'m trying to write from a loop to a data frame in R, for example a loop like this>

for (i in 1:20) {
print(c(i+i,i*i,i/1))}

and to write

Answer 1

Another way would be

do.call("rbind", sapply(1:20, FUN = function(i) c(i+i,i*i,i/1), simplify = FALSE))


     [,1] [,2] [,3]
 [1,]    2    1    1
 [2,]    4    4    2
 [3,]    6    9    3
 [4,]    8   16    4
 [5,]   10   25    5
 [6,]   12   36    6

If you don't specify simplify = FALSE, you have to transpose the result using t. This can be tedious for large structures.

This solution is especially handy if you have a data set on the large side and/or you need to repeat this many many times.

I offer some timings of solutions in this "thread".

> system.time(do.call("rbind", sapply(1:20000, FUN = function(i) c(i+i,i*i,i/1), simplify = FALSE)))
   user  system elapsed 
   0.05    0.00    0.05 

> system.time(ldply(1:20000, function(i)c(i+i, i*i, i/1)))
   user  system elapsed 
   0.14    0.00    0.14 

> system.time({d <- matrix(nrow=20000, ncol=3) 
+ for (i in 1:20000) { d[i,] <- c(i+i, i*i, i/1)}})
   user  system elapsed 
   0.10    0.00    0.09 

> system.time(ldply(1:20000, function(i)c(i+i, i*i, i/1)))
   user  system elapsed 
  62.88    0.00   62.99