CODEWITHSUNDEEP
rloopsdataframefor-loop
Divs
Divs

Reputation: 137

R loop to create data frames with 2 counters

What I want is to create 60 data frames with 500 rows in each. I tried the below code and, while I get no errors, I am not getting the data frames. However, when I do a View on the as.data.frame, I get the view, but no data frame in my environment. I've been trying for three days with various versions of this code:

getDS <- function(x){
  for(i in 1:3){
    for(j in 1:30000){
      ID_i <- data.table(x$ID[j: (j+500)])
    }
  }
  as.data.frame(ID_i)
}

getDS(DATASETNAME)

Upvotes: 2

Views: 100

Answers (2)

Ista
Ista

Reputation: 10437

I'm not sure the description matches the code, so I'm a little unsure what the desired result is. That said, it is usually not helpful to split a data.table because the built-in by-processing makes it unnecessary. If for some reason you do want to split into a list of data.tables you might consider something along the lines of 

getDS <- function(x, n=5, size = nrow(x)/n, column = "ID", reps = 3) {
    x <- x[1:(n*size), ..column]
    index <- rep(1:n, each = size) 
    replicate(reps, split(x, index),
              simplify = FALSE)
}

getDS(data.table(ID = 1:20), n = 5)

Upvotes: 1

akrun
akrun

Reputation: 887531

We can use outer (on a small example)

out1 <- c(outer(1:3, 1:3, Vectorize(function(i, j) list(x$ID[j:(j + 5)]))))
lapply(out1, as.data.table)

--

The issue in the OP's function is that inside the loop, the ID_i gets updated each time i.e. it is not stored. Inorder to do that we can initialize a list and then store it

getDS <- function(x) {
      ID_i <- vector('list', 3)
      for(i in 1:3) {
           for(j in 1:3) {
           ID_i[[i]][[j]] <- data.table(x$ID[j:(j + 5)])
          }
        }
      ID_i
    }

do.call(c, getDS(x))

data

x <- data.table(ID = 1:50)

Upvotes: 2

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