How do you create a data frame using combinations of character strings?

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I am trying to create an data frame that is generated from combinations of a list of character strings in R. For example, the list would be something like

list <- c("liz", "doug", "stacy")

The end output goal would be a data frame that would have rows that allow for each combination to be present, such as this:

 df <- as.data.frame(cbind(c("liz", "liz", "doug"), c("doug", "stacy", "stacy")))

I'm trying to make so that each pair is it's own row, with no repeated combinations. Any thoughts on how to achieve this with larger character lists?

Thanks in advance.

combinations r
1 Answers

expand.grid() will give you all the possible combinations of its vector arguments:

number_of_variables<-2

output<-expand.grid(data.frame(replicate(number_of_variables, list))

>output
     X1    X2
1   liz   liz
2  doug   liz
3 stacy   liz
4   liz  doug
5  doug  doug
6 stacy  doug
7   liz stacy
8  doug stacy
9 stacy stacy

To have every combination as a column call transpose(output)

If you want unique combinations (discard those with the same elements), use combn():

> data.frame(combn(list, number_of_variables))

    X1    X2    X3
1  liz   liz  doug
2 doug stacy stacy
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