How to create a combination with 2 datasets in R

Question

How would I create a dataset with every possible combination from two datasets?

For example, there would be 2 datasets with specific columns in mind:

ds1 = letters[1:4]
ds2 = letters[5:8]

There are also values associated with each letter if that would affect anything (I don't think it should, though)

ds1 = data.frame(a=letters[1:4],b=1:4)
ds2 = data.frame(a=letters[5:8],b=5:8)

In the final dataset, I'd like for there to be every combination of ds1 and ds2 (eg. ae, af, ag, etc.)

At first I thought of using merge, so I tried doing so, but it didn't work. I was thinking that a for-loop would probably be the answer, but I'm not sure as to how I would start.

Suggestions? Thanks!

Answer 1

Perhaps you want expand.grid()? expand.grid() creates a data frame from all combinations of the supplied vectors or factors. letters() contains the 26 lower case letters of the alphabet so we can index the first 4 (A - D) and next four (E - H) to pass into expand.grid()

> expand.grid(letters[1:4], letters[5:8])
   Var1 Var2
1     a    e
2     b    e
3     c    e
4     d    e
5     a    f
6     b    f
7     c    f
8     d    f
9     a    g
10    b    g
11    c    g
12    d    g
13    a    h
14    b    h
15    c    h
16    d    h