[R] Combinations of values in two columns

[Simon Zehnder]

You could use the data.table package
require(data.table)

DT <- data.table(Friend1 = sample(LETTERS, 10, replace = TRUE), Friend2 = sample(LETTERS, 10, replace = TRUE), Indicator = 1)
ALL <- data.table(unique(expand.grid(DT)))
setkey(ALL) 
OTHERS <- ALL[!DT]
OTHERS[, Indicator := 0]

RESULT <- rbind(DT, ALL)

Best

Simon



On 01 Nov 2013, at 10:32, Thomas <Thomas.Chesney at nottingham.ac.uk> wrote:

> I have data that looks like this:
> 
> Friend1, Friend2
> A, B
> A, C
> B, A
> C, D
> 
> And I'd like to generate some more rows and another column. In the new column I'd like to add a 1 beside all the existing rows. That bit's easy enough.
> 
> Then I'd like to add rows for all the possible directed combinations of rows not included in the existing data. So for the above I think that would be:
> 
> A, D
> D, A
> B, C
> C, B
> B, D
> C, A
> D, B
> D, C
> 
> and then put a 0 in the column beside these.
> 
> Can anyone suggest how to do this?
> 
> I'm using R version 2.15.3.
> 
> Thank you,
> 
> Thomas Chesney
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