How to call a variable using a vector and for loop in R

Question

I'm trying to be efficient and use a loop instead of copy-pasting code. I would also like to limit my hard-coding of ID numbers.

I want to loop through a vector containing ID numbers to open and name various data sets with lapply. Here is what I can do via copy-paste to get what I need:

id2174 <- lapply(trials_2174, 
                        FUN = read.table,
                        header = FALSE,
                        sep=",")

id2181 <- lapply(trials_2181, 
                        FUN = read.table,
                        header = FALSE,
                        sep=",")

id2182 <- lapply(trials_2182, 
                        FUN = read.table,
                        header = FALSE,
                        sep=",")

I have a variable named id_nums containing the IDs: 2174, 2181, 2182, 2183, 2185, etc. How do I iterate through these IDs and apply them to the vector argument in lapply, while maintaining the necessary "trials_" part of the vector name? So that it reads like the copy-pasted formula above?

Below is what I've tried, with various changes (single bracket, +, "trials_", etc.) with no success:

EDIT: The trials_2174, trials_2181, etc. variables are file directories. I had used list.files to compile them. Ultimately I need 5 lists of data frames for each ID, not a single list of data frames.

for (i in id_nums) {
  assign(paste0("id",i), lapply(trials_[[i]],
                                 FUN = read.table,
                                 header = FALSE,
                                 sep = ","))
}

It seems like such a simple syntax thing, but I haven't been able to find anything that works. Let me know if I can somehow clarify my question! Thanks!

So are there objects with names ‘trial_2174’ etc? How did they get these names? Are there files with such names in a directory that you can reference? — IRTFM, Mar 30 '22 at 03:59
The objects "trials_2174" etc. are all file directories of varying length per object. 2174 has 64 rows, where 2181 has 50. — Amanda, Mar 30 '22 at 18:23

Abdur Rohman · Answer 1 · 2022-03-30T09:28:14.447

0

Maybe this serves your purpose:

idnum <- c(2174, 2181, 2182, 2183, 2185)

# To create "trials_2174", "trials_2181", etc:
trials <- paste0("trials_", idnum)

# Prepare an empty list to contain the result of read.table later.
# The number of elements of this list equals the length of idnum.
ids <- vector("list", length(idnum))

#Apply `read.table` to trials2174, trials 2181, etc, and 
# store the results in the ids list. 

ids <- lapply(trials, read.table, header = FALSE, sep=",")
names(ids) <-paste0("id", idnum)

edited Mar 30 '22 at 09:28

answered Mar 30 '22 at 09:19

Abdur Rohman

2,691
2
7
12

I'm running into an error with this. I think part of it is that I'm looking for 5 distinct lists for each of the IDs, not one list. The other is that when calling trials in the lapply function, it cannot find the directory. It looks like it's trying to open the directory at "trials_2174" instead of going into the directories within the variable trials_2174. The variable "trials_2174" is a chr [1:64] - 64 addresses for 64 text files. – Amanda Mar 30 '22 at 21:34

How to call a variable using a vector and for loop in R

1 Answers1