[R] interprete wilcox.test results

[Baoqiang Cao]

Dear All,

I am using wilcox.test to test two samples, data_a and data_b, earch sample has 3 replicates, suppose data_a and data_b are 20*3 matrix. Then I used the following to test the null hypothesis (they are from same distribution.):

wilcox.test(x=data_a, y=data_b, alternative="g")
I got pvalue = 1.90806170863311e-09.

When I switched data_a and data_b by doing the following:
wilcox.test(x=data_b, y=data_a, alternative="g")
I got pvalue = 0.999999998111886.

I suppose because I am test them with same null hypothesis, I should get same result (pvalue). Since I am not a savy statistician at all, maybe that is a wrong assumption, could anyone please point out the right interpretion please?

Thanks!

Best,
 Baoqiang