How to Create Dynamic Variable Names in a For Loop in R

Question

I have a dataset/table (called behavioural) with data from 24 participants - these are named in the format: 's1' to 's24'.

The first 6 rows in the table/dataset:

head(behavioural)[c(1,17)]
   subj     recognition_order
1   s1                 2
2   s1                 6
3   s1                 7
4   s1                 8
5   s1                 9
6   s1                10

I want to create a subset for each participant and order each of these subsets by the variable recognition_order

I have created a loop to do this:

behavioural <- read.table("*my file path*\behavioral.txt", header = TRUE)

subj_counter <- 1


for(i in 1:24) {
subject <- paste("s", subj_counter, sep = "")
subset_name <- paste(subject, "_subset", sep="")

[subset_name] <- behavioural[which(behavioural$subj  == subject), ]
[subset_name] <- subset_name[order(subset_name$recognition_order),]

subj_counter = subj_counter + 1

print(subset_name)
print(subj_counter)
}

And I'm pretty sure the logic is solid, except when I run the loop, it does not create 24 subsets. It just creates 1 - s24_subset.

What do I need to do to the bit before "<-" in these 2 lines of code?

[subset_name] <- behavioural[which(behavioural$subj  == subject), ]
[subset_name] <- subset_name[order(subset_name$recognition_order),]

Because [subset_name] isn't working.

I want the [subset_name] to be dynamic - i.e. each time the loop runs, its value changes and it creates a new subset/variable each time.

I have seen things online about the assign() function but I'm not quite sure how to implement this into my loop?

Thank you in advance!

Don't do this. Collect all your similar results into a named list. Something more like this: stackoverflow.com/questions/17499013/…. It will be so much easier for you to work with in the long run. — MrFlick
– MrFlick, Commented Mar 12, 2018 at 18:55
Also, when asking for help, you should include a simple reproducible example with sample input and desired output that can be used to test and verify possible solutions. Make sure all variables are defined. — MrFlick
– MrFlick, Commented Mar 12, 2018 at 18:57
I would suggest using the split function to split your original dataset into a list with the 24 subset. It is much easier to would with a list (using lapply) then the 24 separate dataframes. — Dave2e
– Dave2e, Commented Mar 12, 2018 at 18:58
Mr Flick - the entire code I posted above could be run straight away on someone else's computer, provided they have the 'behavioural.txt' file, but how do I put/attach the text file to this question? — EdinPC
– EdinPC, Commented Mar 12, 2018 at 18:59
@Dave2e - do you mean something like this? my_split_list <- split(behavioural, behavioural$subj)'This creates a very large list, but how do I then sort this by 'recognition_order' per subject? — EdinPC
– EdinPC, Commented Mar 12, 2018 at 19:12

IRTFM · Accepted Answer · 2018-03-12 19:39:23Z

4

If you want to order the items inside the results of a split than just use lapply to pass the needed function calls to do the ordering on a single dataframe at a time (which are re-bundled together by lapply after the ordering:

my_split_list <- split(behavioural, behavioural$subj)
ord.list <- lapply( my_split_list, function(d){ 
                   d[ order(d[['recognition_order']]) , ] }

This is a common paradigm called "split-apply-combine": "The Split-Apply-Combine Strategy for Data Analysis" https://www.jstatsoft.org/article/view/v040i01/v40i01.pdf

answered Mar 12, 2018 at 19:39

IRTFM

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THess · Accepted Answer · 2019-12-11 10:16:36Z

3

for(i in 1:5) {
  assign(paste0("test_",i),i) 
}
test_list <- mget(ls(pattern = "test_"))`

I hope you get a good answer. There is a good way to create an assign function and to bind this pattern in mget. I've outlined a lot of questions for R and Python about dynamically generating variables. Attached to the following link. - Creating Variables Dynamically (R, Python)

edited Dec 11, 2019 at 10:16

THess

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answered Dec 11, 2019 at 8:29

shjj08

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93i7hdjb · Accepted Answer · 2018-03-12 18:54:10Z

0

You can accomplish this with eval() and parse(), like so:

eval(parse(text = paste(subset_name, "<- subset_name[order(subset_name$recognition_order),]", sep = '')))

answered Mar 12, 2018 at 18:54

93i7hdjb

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1 Comment

EdinPC Over a year ago

Hi there, thanks for your answer! Unfortunately, I tried this code and it did not work.

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