[R] Combinations of values in two columns

Chris Campbell ccampbell at mango-solutions.com
Fri Nov 1 11:38:20 CET 2013

Hi Thomas,    
It depends whether you'd like to include all levels of each column in every column. For including all values you could try something like this:    
isAllDifferent <- function(z) !any(duplicated(z))   
myData <- data.frame(Friend1=c("a", "a", "b", "c"), Friend2=c("b", "c", "a", "d"), stringsAsFactors=FALSE)   
friends <- unique(unlist(myData, use.names=FALSE))   
allCombs <- do.call(expand.grid, rep(list(friends), ncol(myData)))    
colnames(allCombs) <- colnames(myData)   
allCombs <- allCombs[apply(allCombs, 1, isAllDifferent),]    
output <- cbind(allCombs, included=1*do.call(paste, allCombs)%in%do.call(paste, myData))     
output[order(output$included, decreasing=TRUE),]      
   Friend1 Friend2 included   
2        b       a        1   
5        a       b        1   
9        a       c        1   
15       c       d        1   
3        c       a        0   
4        d       a        0   
7        c       b        0   
8        d       b        0   
10       b       c        0   
12       d       c        0   
13       a       d        0   
14       b       d        0   
If you only want each column to contain its corresponding values, you could try something like this:   
myData <- data.frame(Friend1=c("a", "a", "b", "c"),   
    Friend2=c("b", "c", "a", "d"), new = 1)  
newData <- expand.grid(Friend1 = unique(myData$Friend1),   
    Friend2 = unique(myData$Friend2))  
output <- merge(myData, newData, all = TRUE)  
output$new[is.na(output$new)] <- 0    
   Friend1 Friend2 new   
1        a       a   0   
2        a       b   1   
3        a       c   1  
4        a       d   0   
5        b       a   1  
6        b       b   0   
7        b       c   0   
8        b       d   0  
9        c       a   0  
10       c       b   0   
11       c       c   0    
12       c       d   1    
I hope this helps.   
Best wishes   

Chris Campbell, PhD   
Tel. +44 (0) 1249 705 450 | Mobile. +44 (0) 7929 628349   
ccampbell at mango-solutions.com | http://www.mango-solutions.com   
Data Analysis that Delivers   
Mango Solutions     
2 Methuen Park, Chippenham, Wiltshire. SN14 OGB UK    
-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Thomas
Sent: 01 November 2013 09:32
To: r-help at r-project.org
Subject: [R] Combinations of values in two columns

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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