What is an alternative to this eval parse code?

Question

I am inserting some code into someone else's custom R package and I don't have flexibility to write it how I would like.

I need to be able to sum up many variables following a similar format that I can re-create with formulas.

I am looking for a more efficient way to write this. Efficiency is important because there is a lot of data to process.

Here is sample code showing what I want to do, but it is slow and clunky. I know eval-parse is not the best way to do this, that's why I'm asking for a better way :-)

v1 <- 1 v2 <- 2 v3 <- 3 v4 <- 4 # this for loop works, but it is clunky and slow string <- character() for (i in 1:4) { if (i < 4) string <- c(string, paste0("v",i,"+")) else string <- c(string, paste0("v",i)) } eval(parse(text=string))

1) You don't need a loop to form the string: paste0("v", 1:4, collapse = "+"). 2) An alternative to @akrun's Reduce can be Reduce("+", mget(ls(pattern = "^v\\d+$"))). — Rui Barradas
– Rui Barradas, Commented Sep 10, 2019 at 18:59
Thanks d.b, I will have to benchmark those methods vs the Reduce solution when I get the chance — datajoel
– datajoel, Commented Sep 10, 2019 at 19:09

akrun · Accepted Answer · 2019-09-11 06:16:11Z

2

We can use Reduce after getting the object values in a list

Reduce(`+`, mget(paste0("v", 1:4)))

answered Sep 11, 2019 at 6:16

akrun

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moodymudskipper · Accepted Answer · 2020-01-03 16:29:44Z

Since you talk about formulas, maybe reformulate() can help

reformulate(paste0("v",1:4)) #> ~v1 + v2 + v3 + v4

You can get your expected output by using the following, though in that case it's less efficient and less intuitive than @akrun's approach :

eval(reformulate(paste0("v",1:4))[[2]]) #> [1] 10

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