R - iterate over a table?

Question

Hi,

I have two tables. Both are read using the read.table() function.

Table 1

    A    B    C
S1  1    1    0
S2  2    0    NA
S3  0    2    1

Table 2

    Pa    Pb    Pc
G1  0.12  0.65  0.001
G2  0.34  0.82  0.03
G3  0.2   0.64  0.87

I need to iterate over both tables. Specifically, I need to iterate over table one column-wise and extract pairwise combinations for each of the entries in a particular column.

For example,

From the first column in table 1, I need to extract the values of all pairwise permutations of the elements in column 1, i.e., {1, 2}, {1, 0},{2, 0}, {2, 1}, {0, 1}, {0, 2}.

Using these values, and an element in Table 2 (this example, element [0, 1]), I will fit to a first order linear regression model.

Does anyone have any suggestions how best to iterate over table one to isolate all those pairwise permutations?

Thanks, S ;-)

Answer 1

For getting the combinations by column in the first table, you can do this:

apply(matrix(1:20, ncol=5), 2, combn, m=2)

It will depend on how you want the final data to look. It might be more sensible as a list:

apply(matrix(1:20, ncol=5), 2, function(x) list(combn(x, m=2)))