Feeding Loop Elements into String Objects in R

Question

So I have two vectors (they are actually the starting rows and the ending rows for which my data presides in in another R object)

start=c(13,103,202,250)
end=c(102,201,249,300)

I am trying to create a loop where I can pull the data using the dataset_{#number}=read.table(text=data[start:end],sep=",",header=F)

n=1
for (i in start){
dataset_{n}=read.table(text=data[i:end[n]],sep=",",header=F)
n=n+1
}

Desired Output:

dataset_1
dataset_2
dataset_3
..

How do I tell the loop to create a brand new data set to save each contiguous block?? How do I tell R that {n} is not a string but part of the loop??

lukeA · Accepted Answer · 2013-12-30 08:00:55Z

1

try assign:

for (i in 1:length(start))
  assign(paste0("dataset_", i), read.table(text=data[start[i]:end[i]], sep=",", header=F))

Answer to your comment:

To combine those datasets, use (a.) either the list approach (if you need the seperate frames, too):

# 1st, create list 
datasets <- mapply(function(from, to) read.table(text=data[from:to], 
                                                sep=",", 
                                                header=F), 
                  start, 
                  end, 
                  SIMPLIFY=FALSE)
# 2nd, combine elements into one data frame
dataset <- do.call(rbind, datasets)

Or (b.) directly combine the data frames in your loop (if you just need the final combined data frame):

dataset <- data.frame()
for (i in 1:length(start))
  dataset <- rbind(dataset, read.table(text=data[start[i]:end[i]], 
                                       sep=",", 
                                       header=F))

edited Dec 30, 2013 at 8:00

answered Dec 30, 2013 at 2:28

lukeA

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6 Comments

lukeA Over a year ago

Or use a list like described here

jessica Over a year ago

Thank you Luke! Though was the assign function necessary? Could the loop have been with just paste("dataset_", i)=read.table(....)??

jessica Over a year ago

I guess better for me to ask is, why is when I tried the loop without the assign command did the loop not work? Sounds pretty intuitive that paste(x,y) would create the stringxy which would be assigned to read.table(..)

lukeA Over a year ago

Assign let's you create new objects with dynamic names. paste(...)=read.table would try to assign a data frame (return value of read.table) to a string constant (return value of paste). This does not work.

jessica Over a year ago

Thanks luke. With the datsets that were generated from the loop I am trying to bind them all row wise. I am encountering the same problem of feeding the loop element into the string. Here is the loop. What am I missing?

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