CODEWITHSUNDEEP
r
user1353751
user1353751

Reputation: 1

How do I call existing sequentially named variables to apply an operation in a for loop

I want to apply a certain operation to several (sequentially named) variables using a for loop to shorten the following piece of code: 

for(i in 1:ncol(data)) {assign(paste('var', i, sep = '.'), my.fun(data[,i]))}

result.1 <- new.fun(var.1)
result.2 <- new.fun(var.2)
result.3 <- new.fun(var.3)
...

so, how do I call the existing variables var.1, var.2, ....? I tried paste here, too, but that didn't work.

Upvotes: 0

Views: 6710

Answers (2)

Greg Snow
Greg Snow

Reputation: 49660

To expand on @Joshua's answer, if your data is already in variables like var.1, var.2, ... then you can combine them into a list using code like:

mydata <- lapply( paste('var.', 1:10, sep=''), get )

or

mydata <- lapply( paste0('var.',1:10), get )

or 

mydata <- lapply( sprintf('var.%d',1:10), get )

With the last one you can use "var%03d" if you have varible names like var001, var002, ...

If you then want the terms in the list named (not needed, but can be nice) you can just do:

names(mydata) <- sprintf('var.%d', 1:10)

Now if you want to access a single element of the list you can access it with mydata[[3]] or mydata$var.3. But the big advantage is that you can now use lapply or sapply or vapply or other tools to run the same function on each element of the list, and if you want to save, copy, delete, etc. the data you just have one object to worry about instead of needing another loop.

For future projects it is best to read or create the data directly into a list to begin with rather than creating the individual variables first.

Upvotes: 6

Joshua Ulrich
Joshua Ulrich

Reputation: 176698

Short answer: don't do that; use a list instead.

Assuming data is a data.frame:

vars <- lapply(data, my.fun)
results <- lapply(vars, new.fun)

Upvotes: 7

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