There are two groups in my database, the first group is called unhealthy group and the other group is healthy group. Each group has 4 variables (Same variables) but different values for similar variables in each group. It means that the rows of unhealthy groups are more than healthy group. I want to show the distance between healthy group and unhealthy group using mahalanobis distance.

 1. 1-In each group we have 4 dimensions so how we can show 4
    dimensions(X1,x2,x3,x4) in a plot.  
 2- Is it possible to draw a line
    from centroid of each group to centroid of another group.

I want to use pairwise.mahalanobis from HDMD package I have to combine two groups in a table, but I have two separate table for each group of variables.
Please give me any Idea to show the distance between these two groups using Mahalanobis distance.