Assign n Email Addresses to x Cells, Intrinsically

Sample Use Case:
Marketing requests that an email address list be divided randomly into a given number of cells so that each cell would receive a different version of copy.
Below is a technique that takes n email addresses and pseudo-randomly assigns each to one of x cells. The advantage of this method is that the user does not need to maintain a log of each email address's assigned cell since the cell assignment can be reproduced at any time.
First, read in a list of email addresses to be assigned.

emails <- c("[email protected]", "[email protected]", "[email protected]", 
    "[email protected]", "[email protected]", "[email protected]", "[email protected]", 
    "[email protected]", "[email protected]", "[email protected]", "[email protected]", 
    "[email protected]", "[email protected]", "[email protected]")
length(emails)

## [1] 14

Next, assign the number of cells.

cells <- 3

Create a vector of the number of characters in each email address.

em.len <- nchar(emails)

Use the modulo function (%%) to create a vector of remainders. 1 is added to the number of cells as a holdout.

em.mod <- em.len%%(cells + 1)

The table function summarizes how many email addresses have been assigned to each cell (including the holdout).

table(em.mod)

## em.mod
## 0 1 2 3 
## 3 3 4 4

Separate the original list of email addresses into the assigned cells.

em.1 <- emails[em.mod == 1]  #  cell 1
em.2 <- emails[em.mod == 2]  #  cell 2
em.3 <- emails[em.mod == 3]  #  cell 3
em.0 <- emails[em.mod == 0]  #  control

Display the email addresses assigned to each cell.

em.1

## [1] "[email protected]"             "[email protected]"                
## [3] "[email protected]"

em.2

## [1] "[email protected]"     "[email protected]"
## [3] "[email protected]"         "[email protected]"

em.3

## [1] "[email protected]"         "[email protected]"
## [3] "[email protected]"     "[email protected]"

em.0

## [1] "[email protected]" "[email protected]"     "[email protected]"

Now each email address has been assigned to a specific number of given cells.
Each email address will always belong to the current cell because the number of characters it has will not change.