How to save simulation data using for loop in R

Question

I am simulating several data sets using for loop in R and saving the data sets in text files in a folder. Since I need to analyze these data sets, I am importing these data from the folder to R and doing my analyses. I am wondering if there is any way to do both simulation and analysis by keeping them in R as data frames instead of saving and importing. Here is my code:

setwd("C:\\Users\\John\\Desktop\\datageneration")

kitem<-10
N<-100
disc<-rnorm(k,0,1)
diff=rnorm(k,0,1)

irtp<-function(t,a,b,pexp)
{
    pexp<-1/(1+exp(-b*(t-a)))
    pexp
}
for( iter in 1:20) 
{
    X<-mat.or.vec(N,kitem)
    P<-mat.or.vec(N,kitem)
    for(i in 1:N)
    {
        theta<-rnorm(N,0,1)
        assign(paste0("theta", iter), theta)
        filename1 <- paste (" theta",iter ,".txt ", sep ="")
        write.table( get(paste0("theta",iter)) , file = filename1 , row.names =FALSE ,col.names = FALSE )
        for(k in 1:kitem)
        {
            P[i,k]<-irtp(theta[i],diff[k],disc[k],pexp)
            X[i,k]<-ifelse(runif(1)<P[i,k],1,0)
            assign(paste0("X",iter), X)         # HERE'S THE PART THAT I NEED HELP
            filename2 <- paste ("X",iter ,".txt ", sep ="")
            write.table( get(paste0("X",iter)) , file = filename2 , row.names =FALSE ,col.names = FALSE )
        }
    }
}

All I want to do is just to use the generated data files (e.g., theta1, theta2, theta3..., theta20) by calling their names(e.g., theta1). Since I am generating thousands of data sets, I would like to know if I can do it without using write.table then read.table functions. I will be very appreciated if you can help me.

Answer 1

Edited to reflect the need for the X matrices: Create a list of 20 + 20 items with your simulation data, and name the members accordingly:

kitem<-10
N<-100
disc<-rnorm(kitem,0,1)  # not ( k, ... )
diff=rnorm(kitem,0,1)   # not ( k, ... )
pexp <- 1                   # ??? - not needed here

# the list that takes all the produced data
mySim <- as.list( NULL )

# function definition reduced to the necessary
irtp <- function( t, a, b ) {  1 / ( 1 + exp( -b * ( t -a ) ) ) }

for( iter in 1:20 )
{
  # create two matrices to be filled later
  X<-mat.or.vec(N,kitem)
  P<-mat.or.vec(N,kitem)

  # create and name the theta component
  theta = mySim[[ iter ]] <- rnorm( N, 0, 1 )
  names( mySim )[ iter ] <- paste ( "theta", iter, sep ="" )

  # fill and save the matrices
  for( i in 1:N )
  {
    for( k in 1:kitem )
    {
      P[i,k]<-irtp(theta[i],diff[k],disc[k] )  #  don"t need this: ,pexp)
      X[i,k]<-ifelse(runif(1)<P[i,k],1,0)
    }
  }
  mySim[[ 20 + iter ]] <- X
  names( mySim )[ 20 + iter ] <- paste ( "X", iter, sep ="" )
}

You can save the list altogether as an R object, if you want that.

Now you can adress each simulation be name:

head( mySim$theta3 )
[1]  0.96068066  0.01966067 -1.25682531 -0.15128916 -0.75950710 -1.22243883

You can add matrices, dataframes etc. to the list

mySim$tau1 <- c( "lists", "take", "everything" )

You can selectively save list members with the corresponding file name:

filename <- paste( names( mySim )[3], ".txt", sep = "" )
write.table( mySim$theta3, filename )

Is that what you had in mind?