Pasting two vectors with combinations of all vectors' elements

Another option using sprintf in combination with expand.grid:

eg <- expand.grid(vis, vars)
sprintf('%s.%s', eg[,2], eg[,1])

which gives:

[1] "SR.1" "SR.2" "SR.3" "PL.1" "PL.2" "PL.3"

Explanation:

• With expand.grid you create all combinations of the two vectors.
• sprintf pastes the two vectors together according to the specified format ('%s.%s'). Each %s part of the format is replaced by the elements of the vectors.

You can use this, but there may be a simpler solution :

R> apply(expand.grid(vars, vis), 1, paste, collapse=".")
[1] "SR.1" "PL.1" "SR.2" "PL.2" "SR.3" "PL.3"

---

expand.grid gives back a data.frame which when used with apply, apply will convert it to a matrix. This is just unnecessary (and inefficient on large data). outer gives a matrix and also takes function argument. It'll be much efficient on huge data as well.

Using outer:

as.vector(outer(vars, vis, paste, sep="."))
# [1] "SR.1" "PL.1" "SR.2" "PL.2" "SR.3" "PL.3"

This old question already has an accepted answer. But as it's being used as dupe target, I believe it's worthwhile to add a data.table solution which uses the cross join function CJ():

library(data.table) 
options(datatable.CJ.names=FALSE) # required with version version 1.12.0+
CJ(vars, vis)[, paste(V1, V2, sep =".")]
#[1] "PL.1" "PL.2" "PL.3" "SR.1" "SR.2" "SR.3"

In case the original order is important:

CJ(vars, vis, sorted = FALSE)[, paste(V1, V2, sep =".")]
#[1] "SR.1" "SR.2" "SR.3" "PL.1" "PL.2" "PL.3"

Edit: CJ() has changed default behaviour with version 1.12.0

As announced in the release notes of version 1.12.0 (Point 3) the default option options(datatable.CJ.names=TRUE) has changed. CJ() now auto-names its inputs exactly as data.table() does.

So, the code above has to be amended for data.table version 1.12.0 and above:

library(data.table)   ### version 1.12.0+
CJ(vars, vis)[, paste(vars, vis, sep =".")]

and

CJ(vars, vis, sorted = FALSE)[, paste(vars, vis, sep =".")]

resp.

Another option is to use the each argument of rep:

paste(rep(vars, each = length(vis)), vis, sep = ".")

I find this more straightforward than the solutions based on apply or expand.grid.